text: /*
   * Copyright 2020 Google LLC
   *
   * Use of this source code is governed by a BSD-style license that can be
   * found in the LICENSE file.
   */
  
  #include "include/private/SkSLProgramElement.h"
  #include "include/private/SkSLStatement.h"
  #include "include/private/SkTArray.h"
  #include "include/private/SkTPin.h"
  #include "src/sksl/SkSLCompiler.h"
  #include "src/sksl/SkSLOperators.h"
  #include "src/sksl/codegen/SkSLCodeGenerator.h"
  #include "src/sksl/codegen/SkSLVMCodeGenerator.h"
  #include "src/sksl/ir/SkSLBinaryExpression.h"
  #include "src/sksl/ir/SkSLBlock.h"
  #include "src/sksl/ir/SkSLBoolLiteral.h"
  #include "src/sksl/ir/SkSLBreakStatement.h"
  #include "src/sksl/ir/SkSLChildCall.h"
  #include "src/sksl/ir/SkSLConstructor.h"
  #include "src/sksl/ir/SkSLConstructorArray.h"
  #include "src/sksl/ir/SkSLConstructorArrayCast.h"
  #include "src/sksl/ir/SkSLConstructorDiagonalMatrix.h"
  #include "src/sksl/ir/SkSLConstructorMatrixResize.h"
  #include "src/sksl/ir/SkSLConstructorSplat.h"
  #include "src/sksl/ir/SkSLConstructorStruct.h"
  #include "src/sksl/ir/SkSLContinueStatement.h"
  #include "src/sksl/ir/SkSLDoStatement.h"
  #include "src/sksl/ir/SkSLExpressionStatement.h"
  #include "src/sksl/ir/SkSLExternalFunctionCall.h"
  #include "src/sksl/ir/SkSLExternalFunctionReference.h"
  #include "src/sksl/ir/SkSLFieldAccess.h"
  #include "src/sksl/ir/SkSLFloatLiteral.h"
  #include "src/sksl/ir/SkSLForStatement.h"
  #include "src/sksl/ir/SkSLFunctionCall.h"
  #include "src/sksl/ir/SkSLFunctionDeclaration.h"
  #include "src/sksl/ir/SkSLFunctionDefinition.h"
  #include "src/sksl/ir/SkSLIfStatement.h"
  #include "src/sksl/ir/SkSLIndexExpression.h"
  #include "src/sksl/ir/SkSLIntLiteral.h"
  #include "src/sksl/ir/SkSLPostfixExpression.h"
  #include "src/sksl/ir/SkSLPrefixExpression.h"
  #include "src/sksl/ir/SkSLReturnStatement.h"
  #include "src/sksl/ir/SkSLSwitchStatement.h"
  #include "src/sksl/ir/SkSLSwizzle.h"
  #include "src/sksl/ir/SkSLTernaryExpression.h"
  #include "src/sksl/ir/SkSLVarDeclarations.h"
  #include "src/sksl/ir/SkSLVariableReference.h"
  
  #include <algorithm>
  #include <unordered_map>
  
  namespace {
      // sksl allows the optimizations of fast_mul(), so we want to use that most of the time.
      // This little sneaky snippet of code lets us use ** as a fast multiply infix operator.
      struct FastF32 { skvm::F32 val; };
      static FastF32 operator*(skvm::F32 y) { return {y}; }
      static skvm::F32 operator*(skvm::F32 x, FastF32 y) { return fast_mul(x, y.val); }
      static skvm::F32 operator*(float     x, FastF32 y) { return fast_mul(x, y.val); }
  }
  
  namespace SkSL {
  
  namespace {
  
  // Holds scalars, vectors, or matrices
  struct Value {
      Value() = default;
      explicit Value(size_t slots) {
          fVals.resize(slots);
      }
      Value(skvm::F32 x) : fVals({ x.id }) {}
      Value(skvm::I32 x) : fVals({ x.id }) {}
  
      explicit operator bool() const { return !fVals.empty(); }
  
      size_t slots() const { return fVals.size(); }
  
      struct ValRef {
          ValRef(skvm::Val& val) : fVal(val) {}
  
          ValRef& operator=(ValRef    v) { fVal = v.fVal; return *this; }
          ValRef& operator=(skvm::Val v) { fVal = v;      return *this; }
          ValRef& operator=(skvm::F32 v) { fVal = v.id;   return *this; }
          ValRef& operator=(skvm::I32 v) { fVal = v.id;   return *this; }
  
          operator skvm::Val() { return fVal; }
  
          skvm::Val& fVal;
      };
  
      ValRef    operator[](size_t i) {
          // These redundant asserts work around what we think is a codegen bug in GCC 8.x for
          // 32-bit x86 Debug builds.
          SkASSERT(i < fVals.size());
          return fVals[i];
      }
      skvm::Val operator[](size_t i) const {
          // These redundant asserts work around what we think is a codegen bug in GCC 8.x for
          // 32-bit x86 Debug builds.
          SkASSERT(i < fVals.size());
          return fVals[i];
      }
  
      SkSpan<skvm::Val> asSpan() { return SkMakeSpan(fVals); }
  
  private:
      SkSTArray<4, skvm::Val, true> fVals;
  };
  
  }  // namespace
  
  class SkVMGenerator {
  public:
      SkVMGenerator(const Program& program,
                    skvm::Builder* builder,
                    SkSpan<skvm::Val> uniforms,
                    skvm::Coord device,
                    skvm::Coord local,
                    SampleShaderFn sampleShader,
                    SampleColorFilterFn sampleColorFilter,
                    SampleBlenderFn sampleBlender);
  
      void writeFunction(const FunctionDefinition& function,
                         SkSpan<skvm::Val> arguments,
                         SkSpan<skvm::Val> outReturn);
  
  private:
      /**
       * In SkSL, a Variable represents a named, typed value (along with qualifiers, etc).
       * Every Variable is mapped to one (or several, contiguous) indices into our vector of
       * skvm::Val. Those skvm::Val entries hold the current actual value of that variable.
       *
       * NOTE: Conceptually, each Variable is just mapped to a Value. We could implement it that way,
       * (and eliminate the indirection), but it would add overhead for each Variable,
       * and add additional (different) bookkeeping for things like lvalue-swizzles.
       *
       * Any time a variable appears in an expression, that's a VariableReference, which is a kind of
       * Expression. Evaluating that VariableReference (or any other Expression) produces a Value,
       * which is a set of skvm::Val. (This allows an Expression to produce a vector or matrix, in
       * addition to a scalar).
       *
       * For a VariableReference, producing a Value is straightforward - we get the slot of the
       * Variable (from fVariableMap), use that to look up the current skvm::Vals holding the
       * variable's contents, and construct a Value with those ids.
       */
  
      /**
       * Returns the slot holding v's Val(s). Allocates storage if this is first time 'v' is
       * referenced. Compound variables (e.g. vectors) will consume more than one slot, with
       * getSlot returning the start of the contiguous chunk of slots.
       */
      size_t getSlot(const Variable& v);
  
      skvm::F32 f32(skvm::Val id) { SkASSERT(id != skvm::NA); return {fBuilder, id}; }
      skvm::I32 i32(skvm::Val id) { SkASSERT(id != skvm::NA); return {fBuilder, id}; }
  
      // Shorthand for scalars
      skvm::F32 f32(const Value& v) { SkASSERT(v.slots() == 1); return f32(v[0]); }
      skvm::I32 i32(const Value& v) { SkASSERT(v.slots() == 1); return i32(v[0]); }
  
      template <typename Fn>
      Value unary(const Value& v, Fn&& fn) {
          Value result(v.slots());
          for (size_t i = 0; i < v.slots(); ++i) {
              result[i] = fn({fBuilder, v[i]});
          }
          return result;
      }
  
      skvm::I32 mask() {
          // As we encounter (possibly conditional) return statements, fReturned is updated to store
          // the lanes that have already returned. For the remainder of the current function, those
          // lanes should be disabled.
          return fConditionMask & fLoopMask & ~currentFunction().fReturned;
      }
  
      size_t fieldSlotOffset(const FieldAccess& expr);
      size_t indexSlotOffset(const IndexExpression& expr);
  
      Value writeExpression(const Expression& expr);
      Value writeBinaryExpression(const BinaryExpression& b);
      Value writeAggregationConstructor(const AnyConstructor& c);
      Value writeChildCall(const ChildCall& c);
      Value writeConstructorDiagonalMatrix(const ConstructorDiagonalMatrix& c);
      Value writeConstructorMatrixResize(const ConstructorMatrixResize& c);
      Value writeConstructorCast(const AnyConstructor& c);
      Value writeConstructorSplat(const ConstructorSplat& c);
      Value writeFunctionCall(const FunctionCall& c);
      Value writeExternalFunctionCall(const ExternalFunctionCall& c);
      Value writeFieldAccess(const FieldAccess& expr);
      Value writeIndexExpression(const IndexExpression& expr);
      Value writeIntrinsicCall(const FunctionCall& c);
      Value writePostfixExpression(const PostfixExpression& p);
      Value writePrefixExpression(const PrefixExpression& p);
      Value writeSwizzle(const Swizzle& swizzle);
      Value writeTernaryExpression(const TernaryExpression& t);
      Value writeVariableExpression(const VariableReference& expr);
  
      Value writeTypeConversion(const Value& src, Type::NumberKind srcKind, Type::NumberKind dstKind);
  
      void writeStatement(const Statement& s);
      void writeBlock(const Block& b);
      void writeBreakStatement();
      void writeContinueStatement();
      void writeForStatement(const ForStatement& f);
      void writeIfStatement(const IfStatement& stmt);
      void writeReturnStatement(const ReturnStatement& r);
      void writeVarDeclaration(const VarDeclaration& decl);
  
      Value writeStore(const Expression& lhs, const Value& rhs);
  
      Value writeMatrixInverse2x2(const Value& m);
      Value writeMatrixInverse3x3(const Value& m);
      Value writeMatrixInverse4x4(const Value& m);
  
      //
      // Global state for the lifetime of the generator:
      //
      const Program& fProgram;
      skvm::Builder* fBuilder;
  
      const skvm::Coord fLocalCoord;
      const SampleShaderFn fSampleShader;
      const SampleColorFilterFn fSampleColorFilter;
      const SampleBlenderFn fSampleBlender;
  
      // [Variable, first slot in fSlots]
      std::unordered_map<const Variable*, size_t> fVariableMap;
      std::vector<skvm::Val> fSlots;
  
      // Conditional execution mask (managed by ScopedCondition, and tied to control-flow scopes)
      skvm::I32 fConditionMask;
  
      // Similar: loop execution masks. Each loop starts with all lanes active (fLoopMask).
      // 'break' disables a lane in fLoopMask until the loop finishes
      // 'continue' disables a lane in fLoopMask, and sets fContinueMask to be re-enabled on the next
      //   iteration
      skvm::I32 fLoopMask;
      skvm::I32 fContinueMask;
  
      //
      // State that's local to the generation of a single function:
      //
      struct Function {
          const SkSpan<skvm::Val> fReturnValue;
          skvm::I32               fReturned;
      };
      std::vector<Function> fFunctionStack;
      Function& currentFunction() { return fFunctionStack.back(); }
  
      class ScopedCondition {
      public:
          ScopedCondition(SkVMGenerator* generator, skvm::I32 mask)
                  : fGenerator(generator), fOldConditionMask(fGenerator->fConditionMask) {
              fGenerator->fConditionMask &= mask;
          }
  
          ~ScopedCondition() { fGenerator->fConditionMask = fOldConditionMask; }
  
      private:
          SkVMGenerator* fGenerator;
          skvm::I32 fOldConditionMask;
      };
  };
  
  static Type::NumberKind base_number_kind(const Type& type) {
      if (type.typeKind() == Type::TypeKind::kMatrix || type.typeKind() == Type::TypeKind::kVector) {
          return base_number_kind(type.componentType());
      }
      return type.numberKind();
  }
  
  static inline bool is_uniform(const SkSL::Variable& var) {
      return var.modifiers().fFlags & Modifiers::kUniform_Flag;
  }
  
  SkVMGenerator::SkVMGenerator(const Program& program,
                               skvm::Builder* builder,
                               SkSpan<skvm::Val> uniforms,
                               skvm::Coord device,
                               skvm::Coord local,
                               SampleShaderFn sampleShader,
                               SampleColorFilterFn sampleColorFilter,
                               SampleBlenderFn sampleBlender)
          : fProgram(program)
          , fBuilder(builder)
          , fLocalCoord(local)
          , fSampleShader(std::move(sampleShader))
          , fSampleColorFilter(std::move(sampleColorFilter))
          , fSampleBlender(std::move(sampleBlender)) {
      fConditionMask = fLoopMask = fBuilder->splat(0xffff'ffff);
  
      // Now, add storage for each global variable (including uniforms) to fSlots, and entries in
      // fVariableMap to remember where every variable is stored.
      const skvm::Val* uniformIter = uniforms.begin();
      size_t fpCount = 0;
      for (const ProgramElement* e : fProgram.elements()) {
          if (e->is<GlobalVarDeclaration>()) {
              const GlobalVarDeclaration& gvd = e->as<GlobalVarDeclaration>();
              const VarDeclaration& decl = gvd.declaration()->as<VarDeclaration>();
              const Variable& var = decl.var();
              SkASSERT(fVariableMap.find(&var) == fVariableMap.end());
  
              // For most variables, fVariableMap stores an index into fSlots, but for children,
              // fVariableMap stores the index to pass to fSample(Shader|ColorFilter|Blender)
              if (var.type().isEffectChild()) {
                  fVariableMap[&var] = fpCount++;
                  continue;
              }
  
              // Opaque types include fragment processors, GL objects (samplers, textures, etc), and
              // special types like 'void'. Of those, only fragment processors are legal variables.
              SkASSERT(!var.type().isOpaque());
  
              // getSlot() allocates space for the variable's value in fSlots, initializes it to zero,
              // and populates fVariableMap.
              size_t slot   = this->getSlot(var),
                     nslots = var.type().slotCount();
  
              if (int builtin = var.modifiers().fLayout.fBuiltin; builtin >= 0) {
                  // builtin variables are system-defined, with special semantics. The only builtin
                  // variable exposed to runtime effects is sk_FragCoord.
                  switch (builtin) {
                      case SK_FRAGCOORD_BUILTIN:
                          SkASSERT(nslots == 4);
                          fSlots[slot + 0] = device.x.id;
                          fSlots[slot + 1] = device.y.id;
                          fSlots[slot + 2] = fBuilder->splat(0.0f).id;
                          fSlots[slot + 3] = fBuilder->splat(1.0f).id;
                          break;
                      default:
                          SkDEBUGFAIL("Unsupported builtin");
                  }
              } else if (is_uniform(var)) {
                  // For uniforms, copy the supplied IDs over
                  SkASSERT(uniformIter + nslots <= uniforms.end());
                  std::copy(uniformIter, uniformIter + nslots, fSlots.begin() + slot);
                  uniformIter += nslots;
              } else if (decl.value()) {
                  // For other globals, populate with the initializer expression (if there is one)
                  Value val = this->writeExpression(*decl.value());
                  for (size_t i = 0; i < nslots; ++i) {
                      fSlots[slot + i] = val[i];
                  }
              }
          }
      }
      SkASSERT(uniformIter == uniforms.end());
  }
  
  void SkVMGenerator::writeFunction(const FunctionDefinition& function,
                                    SkSpan<skvm::Val> arguments,
                                    SkSpan<skvm::Val> outReturn) {
      const FunctionDeclaration& decl = function.declaration();
      SkASSERT(decl.returnType().slotCount() == outReturn.size());
  
      fFunctionStack.push_back({outReturn, /*returned=*/fBuilder->splat(0)});
  
      // For all parameters, copy incoming argument IDs to our vector of (all) variable IDs
      size_t argIdx = 0;
      for (const Variable* p : decl.parameters()) {
          size_t paramSlot = this->getSlot(*p),
                 nslots    = p->type().slotCount();
  
          for (size_t i = 0; i < nslots; ++i) {
              fSlots[paramSlot + i] = arguments[argIdx + i];
          }
          argIdx += nslots;
      }
      SkASSERT(argIdx == arguments.size());
  
      this->writeStatement(*function.body());
  
      // Copy 'out' and 'inout' parameters back to their caller-supplied argument storage
      argIdx = 0;
      for (const Variable* p : decl.parameters()) {
          size_t nslots = p->type().slotCount();
  
          if (p->modifiers().fFlags & Modifiers::kOut_Flag) {
              size_t paramSlot = this->getSlot(*p);
              for (size_t i = 0; i < nslots; ++i) {
                  arguments[argIdx + i] = fSlots[paramSlot + i];
              }
          }
          argIdx += nslots;
      }
      SkASSERT(argIdx == arguments.size());
  
      fFunctionStack.pop_back();
  }
  
  size_t SkVMGenerator::getSlot(const Variable& v) {
      auto entry = fVariableMap.find(&v);
      if (entry != fVariableMap.end()) {
          return entry->second;
      }
  
      size_t slot   = fSlots.size(),
             nslots = v.type().slotCount();
      fSlots.resize(slot + nslots, fBuilder->splat(0.0f).id);
      fVariableMap[&v] = slot;
      return slot;
  }
  
  Value SkVMGenerator::writeBinaryExpression(const BinaryExpression& b) {
      const Expression& left = *b.left();
      const Expression& right = *b.right();
      Operator op = b.getOperator();
      if (op.kind() == Token::Kind::TK_EQ) {
          return this->writeStore(left, this->writeExpression(right));
      }
  
      const Type& lType = left.type();
      const Type& rType = right.type();
      bool lVecOrMtx = (lType.isVector() || lType.isMatrix());
      bool rVecOrMtx = (rType.isVector() || rType.isMatrix());
      bool isAssignment = op.isAssignment();
      if (isAssignment) {
          op = op.removeAssignment();
      }
      Type::NumberKind nk = base_number_kind(lType);
  
      // A few ops require special treatment:
      switch (op.kind()) {
          case Token::Kind::TK_LOGICALAND: {
              SkASSERT(!isAssignment);
              SkASSERT(nk == Type::NumberKind::kBoolean);
              skvm::I32 lVal = i32(this->writeExpression(left));
              ScopedCondition shortCircuit(this, lVal);
              skvm::I32 rVal = i32(this->writeExpression(right));
              return lVal & rVal;
          }
          case Token::Kind::TK_LOGICALOR: {
              SkASSERT(!isAssignment);
              SkASSERT(nk == Type::NumberKind::kBoolean);
              skvm::I32 lVal = i32(this->writeExpression(left));
              ScopedCondition shortCircuit(this, ~lVal);
              skvm::I32 rVal = i32(this->writeExpression(right));
              return lVal | rVal;
          }
          case Token::Kind::TK_COMMA:
              // We write the left side of the expression to preserve its side effects, even though we
              // immediately discard the result.
              this->writeExpression(left);
              return this->writeExpression(right);
          default:
              break;
      }
  
      // All of the other ops always evaluate both sides of the expression
      Value lVal = this->writeExpression(left),
            rVal = this->writeExpression(right);
  
      // Special case for M*V, V*M, M*M (but not V*V!)
      if (op.kind() == Token::Kind::TK_STAR
          && lVecOrMtx && rVecOrMtx && !(lType.isVector() && rType.isVector())) {
          int rCols = rType.columns(),
              rRows = rType.rows(),
              lCols = lType.columns(),
              lRows = lType.rows();
          // M*V treats the vector as a column
          if (rType.isVector()) {
              std::swap(rCols, rRows);
          }
          SkASSERT(lCols == rRows);
          SkASSERT(b.type().slotCount() == static_cast<size_t>(lRows * rCols));
          Value result(lRows * rCols);
          size_t resultIdx = 0;
          for (int c = 0; c < rCols; ++c)
          for (int r = 0; r < lRows; ++r) {
              skvm::F32 sum = fBuilder->splat(0.0f);
              for (int j = 0; j < lCols; ++j) {
                  sum += f32(lVal[j*lRows + r]) * f32(rVal[c*rRows + j]);
              }
              result[resultIdx++] = sum;
          }
          SkASSERT(resultIdx == result.slots());
          return isAssignment ? this->writeStore(left, result) : result;
      }
  
      size_t nslots = std::max(lVal.slots(), rVal.slots());
  
      auto binary = [&](auto&& f_fn, auto&& i_fn) {
          Value result(nslots);
          for (size_t i = 0; i < nslots; ++i) {
              // If one side is scalar, replicate it to all channels
              skvm::Val L = lVal.slots() == 1 ? lVal[0] : lVal[i],
                        R = rVal.slots() == 1 ? rVal[0] : rVal[i];
              if (nk == Type::NumberKind::kFloat) {
                  result[i] = f_fn(f32(L), f32(R));
              } else {
                  result[i] = i_fn(i32(L), i32(R));
              }
          }
          return isAssignment ? this->writeStore(left, result) : result;
      };
  
      auto unsupported_f = [&](skvm::F32, skvm::F32) {
          SkDEBUGFAIL("Unsupported operator");
          return skvm::F32{};
      };
  
      switch (op.kind()) {
          case Token::Kind::TK_EQEQ: {
              SkASSERT(!isAssignment);
              Value cmp = binary([](skvm::F32 x, skvm::F32 y) { return x == y; },
                                 [](skvm::I32 x, skvm::I32 y) { return x == y; });
              skvm::I32 folded = i32(cmp[0]);
              for (size_t i = 1; i < nslots; ++i) {
                  folded &= i32(cmp[i]);
              }
              return folded;
          }
          case Token::Kind::TK_NEQ: {
              SkASSERT(!isAssignment);
              Value cmp = binary([](skvm::F32 x, skvm::F32 y) { return x != y; },
                                 [](skvm::I32 x, skvm::I32 y) { return x != y; });
              skvm::I32 folded = i32(cmp[0]);
              for (size_t i = 1; i < nslots; ++i) {
                  folded |= i32(cmp[i]);
              }
              return folded;
          }
          case Token::Kind::TK_GT:
              return binary([](skvm::F32 x, skvm::F32 y) { return x > y; },
                            [](skvm::I32 x, skvm::I32 y) { return x > y; });
          case Token::Kind::TK_GTEQ:
              return binary([](skvm::F32 x, skvm::F32 y) { return x >= y; },
                            [](skvm::I32 x, skvm::I32 y) { return x >= y; });
          case Token::Kind::TK_LT:
              return binary([](skvm::F32 x, skvm::F32 y) { return x < y; },
                            [](skvm::I32 x, skvm::I32 y) { return x < y; });
          case Token::Kind::TK_LTEQ:
              return binary([](skvm::F32 x, skvm::F32 y) { return x <= y; },
                            [](skvm::I32 x, skvm::I32 y) { return x <= y; });
  
          case Token::Kind::TK_PLUS:
              return binary([](skvm::F32 x, skvm::F32 y) { return x + y; },
                            [](skvm::I32 x, skvm::I32 y) { return x + y; });
          case Token::Kind::TK_MINUS:
              return binary([](skvm::F32 x, skvm::F32 y) { return x - y; },
                            [](skvm::I32 x, skvm::I32 y) { return x - y; });
          case Token::Kind::TK_STAR:
              return binary([](skvm::F32 x, skvm::F32 y) { return x ** y; },
                            [](skvm::I32 x, skvm::I32 y) { return x * y; });
          case Token::Kind::TK_SLASH:
              // Minimum spec (GLSL ES 1.0) has very loose requirements for integer operations.
              // (Low-end GPUs may not have integer ALUs). Given that, we are allowed to do floating
              // point division plus rounding. Section 10.28 of the spec even clarifies that the
              // rounding mode is undefined (but round-towards-zero is the obvious/common choice).
              return binary([](skvm::F32 x, skvm::F32 y) { return x / y; },
                            [](skvm::I32 x, skvm::I32 y) {
                                return skvm::trunc(skvm::to_F32(x) / skvm::to_F32(y));
                            });
  
          case Token::Kind::TK_BITWISEXOR:
          case Token::Kind::TK_LOGICALXOR:
              return binary(unsupported_f, [](skvm::I32 x, skvm::I32 y) { return x ^ y; });
          case Token::Kind::TK_BITWISEAND:
              return binary(unsupported_f, [](skvm::I32 x, skvm::I32 y) { return x & y; });
          case Token::Kind::TK_BITWISEOR:
              return binary(unsupported_f, [](skvm::I32 x, skvm::I32 y) { return x | y; });
  
          // These three operators are all 'reserved' (illegal) in our minimum spec, but will require
          // implementation in the future.
          case Token::Kind::TK_PERCENT:
          case Token::Kind::TK_SHL:
          case Token::Kind::TK_SHR:
          default:
              SkDEBUGFAIL("Unsupported operator");
              return {};
      }
  }
  
  Value SkVMGenerator::writeAggregationConstructor(const AnyConstructor& c) {
      Value result(c.type().slotCount());
      size_t resultIdx = 0;
      for (const auto &arg : c.argumentSpan()) {
          Value tmp = this->writeExpression(*arg);
          for (size_t tmpSlot = 0; tmpSlot < tmp.slots(); ++tmpSlot) {
              result[resultIdx++] = tmp[tmpSlot];
          }
      }
      return result;
  }
  
  Value SkVMGenerator::writeTypeConversion(const Value& src,
                                           Type::NumberKind srcKind,
                                           Type::NumberKind dstKind) {
      // Conversion among "similar" types (floatN <-> halfN), (shortN <-> intN), etc. is a no-op.
      if (srcKind == dstKind) {
          return src;
      }
  
      // TODO: Handle signed vs. unsigned. GLSL ES 1.0 only has 'int', so no problem yet.
      Value dst(src.slots());
      switch (dstKind) {
          case Type::NumberKind::kFloat:
              if (srcKind == Type::NumberKind::kSigned) {
                  // int -> float
                  for (size_t i = 0; i < src.slots(); ++i) {
                      dst[i] = skvm::to_F32(i32(src[i]));
                  }
                  return dst;
              }
              if (srcKind == Type::NumberKind::kBoolean) {
                  // bool -> float
                  for (size_t i = 0; i < src.slots(); ++i) {
                      dst[i] = skvm::select(i32(src[i]), 1.0f, 0.0f);
                  }
                  return dst;
              }
              break;
  
          case Type::NumberKind::kSigned:
              if (srcKind == Type::NumberKind::kFloat) {
                  // float -> int
                  for (size_t i = 0; i < src.slots(); ++i) {
                      dst[i] = skvm::trunc(f32(src[i]));
                  }
                  return dst;
              }
              if (srcKind == Type::NumberKind::kBoolean) {
                  // bool -> int
                  for (size_t i = 0; i < src.slots(); ++i) {
                      dst[i] = skvm::select(i32(src[i]), 1, 0);
                  }
                  return dst;
              }
              break;
  
          case Type::NumberKind::kBoolean:
              if (srcKind == Type::NumberKind::kSigned) {
                  // int -> bool
                  for (size_t i = 0; i < src.slots(); ++i) {
                      dst[i] = i32(src[i]) != 0;
                  }
                  return dst;
              }
              if (srcKind == Type::NumberKind::kFloat) {
                  // float -> bool
                  for (size_t i = 0; i < src.slots(); ++i) {
                      dst[i] = f32(src[i]) != 0.0;
                  }
                  return dst;
              }
              break;
  
          default:
              break;
      }
      SkDEBUGFAILF("Unsupported type conversion: %d -> %d", (int)srcKind, (int)dstKind);
      return {};
  }
  
  Value SkVMGenerator::writeConstructorCast(const AnyConstructor& c) {
      auto arguments = c.argumentSpan();
      SkASSERT(arguments.size() == 1);
      const Expression& argument = *arguments.front();
  
      const Type& srcType = argument.type();
      const Type& dstType = c.type();
      Type::NumberKind srcKind = base_number_kind(srcType);
      Type::NumberKind dstKind = base_number_kind(dstType);
      Value src = this->writeExpression(argument);
      return this->writeTypeConversion(src, srcKind, dstKind);
  }
  
  Value SkVMGenerator::writeConstructorSplat(const ConstructorSplat& c) {
      SkASSERT(c.type().isVector());
      SkASSERT(c.argument()->type().isScalar());
      int columns = c.type().columns();
  
      // Splat the argument across all components of a vector.
      Value src = this->writeExpression(*c.argument());
      Value dst(columns);
      for (int i = 0; i < columns; ++i) {
          dst[i] = src[0];
      }
      return dst;
  }
  
  Value SkVMGenerator::writeConstructorDiagonalMatrix(const ConstructorDiagonalMatrix& ctor) {
      const Type& dstType = ctor.type();
      SkASSERT(dstType.isMatrix());
      SkASSERT(ctor.argument()->type() == dstType.componentType());
  
      Value src = this->writeExpression(*ctor.argument());
      Value dst(dstType.rows() * dstType.columns());
      size_t dstIndex = 0;
  
      // Matrix-from-scalar builds a diagonal scale matrix
      for (int c = 0; c < dstType.columns(); ++c) {
          for (int r = 0; r < dstType.rows(); ++r) {
              dst[dstIndex++] = (c == r ? f32(src) : fBuilder->splat(0.0f));
          }
      }
  
      SkASSERT(dstIndex == dst.slots());
      return dst;
  }
  
  Value SkVMGenerator::writeConstructorMatrixResize(const ConstructorMatrixResize& ctor) {
      const Type& srcType = ctor.argument()->type();
      const Type& dstType = ctor.type();
      Value src = this->writeExpression(*ctor.argument());
      Value dst(dstType.rows() * dstType.columns());
  
      // Matrix-from-matrix uses src where it overlaps, and fills in missing fields with identity.
      size_t dstIndex = 0;
      for (int c = 0; c < dstType.columns(); ++c) {
          for (int r = 0; r < dstType.rows(); ++r) {
              if (c < srcType.columns() && r < srcType.rows()) {
                  dst[dstIndex++] = src[c * srcType.rows() + r];
              } else {
                  dst[dstIndex++] = fBuilder->splat(c == r ? 1.0f : 0.0f);
              }
          }
      }
  
      SkASSERT(dstIndex == dst.slots());
      return dst;
  }
  
  size_t SkVMGenerator::fieldSlotOffset(const FieldAccess& expr) {
      size_t offset = 0;
      for (int i = 0; i < expr.fieldIndex(); ++i) {
          offset += (*expr.base()->type().fields()[i].fType).slotCount();
      }
      return offset;
  }
  
  Value SkVMGenerator::writeFieldAccess(const FieldAccess& expr) {
      Value base = this->writeExpression(*expr.base());
      Value field(expr.type().slotCount());
      size_t offset = this->fieldSlotOffset(expr);
      for (size_t i = 0; i < field.slots(); ++i) {
          field[i] = base[offset + i];
      }
      return field;
  }
  
  size_t SkVMGenerator::indexSlotOffset(const IndexExpression& expr) {
      Value index = this->writeExpression(*expr.index());
      int indexValue = -1;
      SkAssertResult(fBuilder->allImm(index[0], &indexValue));
  
      // When indexing by a literal, the front-end guarantees that we don't go out of bounds.
      // But when indexing by a loop variable, it's possible to generate out-of-bounds access.
      // The GLSL spec leaves that behavior undefined - we'll just clamp everything here.
      indexValue = SkTPin(indexValue, 0, expr.base()->type().columns() - 1);
  
      size_t stride = expr.type().slotCount();
      return indexValue * stride;
  }
  
  Value SkVMGenerator::writeIndexExpression(const IndexExpression& expr) {
      Value base = this->writeExpression(*expr.base());
      Value element(expr.type().slotCount());
      size_t offset = this->indexSlotOffset(expr);
      for (size_t i = 0; i < element.slots(); ++i) {
          element[i] = base[offset + i];
      }
      return element;
  }
  
  Value SkVMGenerator::writeVariableExpression(const VariableReference& expr) {
      size_t slot = this->getSlot(*expr.variable());
      Value val(expr.type().slotCount());
      for (size_t i = 0; i < val.slots(); ++i) {
          val[i] = fSlots[slot + i];
      }
      return val;
  }
  
  Value SkVMGenerator::writeMatrixInverse2x2(const Value& m) {
      SkASSERT(m.slots() == 4);
      skvm::F32 a = f32(m[0]),
                b = f32(m[1]),
                c = f32(m[2]),
                d = f32(m[3]);
      skvm::F32 idet = 1.0f / (a*d - b*c);
  
      Value result(m.slots());
      result[0] = ( d ** idet);
      result[1] = (-b ** idet);
      result[2] = (-c ** idet);
      result[3] = ( a ** idet);
      return result;
  }
  
  Value SkVMGenerator::writeMatrixInverse3x3(const Value& m) {
      SkASSERT(m.slots() == 9);
      skvm::F32 a11 = f32(m[0]), a12 = f32(m[3]), a13 = f32(m[6]),
                a21 = f32(m[1]), a22 = f32(m[4]), a23 = f32(m[7]),
                a31 = f32(m[2]), a32 = f32(m[5]), a33 = f32(m[8]);
      skvm::F32 idet = 1.0f / (a11*a22*a33 + a12*a23*a31 + a13*a21*a32 -
                               a11*a23*a32 - a12*a21*a33 - a13*a22*a31);
  
      Value result(m.slots());
      result[0] = ((a22**a33 - a23**a32) ** idet);
      result[1] = ((a23**a31 - a21**a33) ** idet);
      result[2] = ((a21**a32 - a22**a31) ** idet);
      result[3] = ((a13**a32 - a12**a33) ** idet);
      result[4] = ((a11**a33 - a13**a31) ** idet);
      result[5] = ((a12**a31 - a11**a32) ** idet);
      result[6] = ((a12**a23 - a13**a22) ** idet);
      result[7] = ((a13**a21 - a11**a23) ** idet);
      result[8] = ((a11**a22 - a12**a21) ** idet);
      return result;
  }
  
  Value SkVMGenerator::writeMatrixInverse4x4(const Value& m) {
      SkASSERT(m.slots() == 16);
      skvm::F32 a00 = f32(m[0]), a10 = f32(m[4]), a20 = f32(m[ 8]), a30 = f32(m[12]),
                a01 = f32(m[1]), a11 = f32(m[5]), a21 = f32(m[ 9]), a31 = f32(m[13]),
                a02 = f32(m[2]), a12 = f32(m[6]), a22 = f32(m[10]), a32 = f32(m[14]),
                a03 = f32(m[3]), a13 = f32(m[7]), a23 = f32(m[11]), a33 = f32(m[15]);
  
      skvm::F32 b00 = a00**a11 - a01**a10,
                b01 = a00**a12 - a02**a10,
                b02 = a00**a13 - a03**a10,
                b03 = a01**a12 - a02**a11,
                b04 = a01**a13 - a03**a11,
                b05 = a02**a13 - a03**a12,
                b06 = a20**a31 - a21**a30,
                b07 = a20**a32 - a22**a30,
                b08 = a20**a33 - a23**a30,
                b09 = a21**a32 - a22**a31,
                b10 = a21**a33 - a23**a31,
                b11 = a22**a33 - a23**a32;
  
      skvm::F32 idet = 1.0f / (b00**b11 - b01**b10 + b02**b09 + b03**b08 - b04**b07 + b05**b06);
  
      b00 *= idet;
      b01 *= idet;
      b02 *= idet;
      b03 *= idet;
      b04 *= idet;
      b05 *= idet;
      b06 *= idet;
      b07 *= idet;
      b08 *= idet;
      b09 *= idet;
      b10 *= idet;
      b11 *= idet;
  
      Value result(m.slots());
      result[ 0] = (a11*b11 - a12*b10 + a13*b09);
      result[ 1] = (a02*b10 - a01*b11 - a03*b09);
      result[ 2] = (a31*b05 - a32*b04 + a33*b03);
      result[ 3] = (a22*b04 - a21*b05 - a23*b03);
      result[ 4] = (a12*b08 - a10*b11 - a13*b07);
      result[ 5] = (a00*b11 - a02*b08 + a03*b07);
      result[ 6] = (a32*b02 - a30*b05 - a33*b01);
      result[ 7] = (a20*b05 - a22*b02 + a23*b01);
      result[ 8] = (a10*b10 - a11*b08 + a13*b06);
      result[ 9] = (a01*b08 - a00*b10 - a03*b06);
      result[10] = (a30*b04 - a31*b02 + a33*b00);
      result[11] = (a21*b02 - a20*b04 - a23*b00);
      result[12] = (a11*b07 - a10*b09 - a12*b06);
      result[13] = (a00*b09 - a01*b07 + a02*b06);
      result[14] = (a31*b01 - a30*b03 - a32*b00);
      result[15] = (a20*b03 - a21*b01 + a22*b00);
      return result;
  }
  
  Value SkVMGenerator::writeChildCall(const ChildCall& c) {
      auto child_it = fVariableMap.find(&c.child());
      SkASSERT(child_it != fVariableMap.end());
  
      const Expression* arg = c.arguments()[0].get();
      Value argVal = this->writeExpression(*arg);
      skvm::Color color;
  
      switch (c.child().type().typeKind()) {
          case Type::TypeKind::kShader: {
              SkASSERT(c.arguments().size() == 1);
              SkASSERT(arg->type() == *fProgram.fContext->fTypes.fFloat2);
              skvm::Coord coord = {f32(argVal[0]), f32(argVal[1])};
              color = fSampleShader(child_it->second, coord);
              break;
          }
          case Type::TypeKind::kColorFilter: {
              SkASSERT(c.arguments().size() == 1);
              SkASSERT(arg->type() == *fProgram.fContext->fTypes.fHalf4 ||
                       arg->type() == *fProgram.fContext->fTypes.fFloat4);
              skvm::Color inColor = {f32(argVal[0]), f32(argVal[1]), f32(argVal[2]), f32(argVal[3])};
              color = fSampleColorFilter(child_it->second, inColor);
              break;
          }
          case Type::TypeKind::kBlender: {
              SkASSERT(c.arguments().size() == 2);
              SkASSERT(arg->type() == *fProgram.fContext->fTypes.fHalf4 ||
                       arg->type() == *fProgram.fContext->fTypes.fFloat4);
              skvm::Color srcColor = {f32(argVal[0]), f32(argVal[1]), f32(argVal[2]), f32(argVal[3])};
  
              arg = c.arguments()[1].get();
              argVal = this->writeExpression(*arg);
              SkASSERT(arg->type() == *fProgram.fContext->fTypes.fHalf4 ||
                       arg->type() == *fProgram.fContext->fTypes.fFloat4);
              skvm::Color dstColor = {f32(argVal[0]), f32(argVal[1]), f32(argVal[2]), f32(argVal[3])};
  
              color = fSampleBlender(child_it->second, srcColor, dstColor);
              break;
          }
          default: {
              SkDEBUGFAILF("cannot sample from type '%s'", c.child().type().description().c_str());
          }
      }
  
      Value result(4);
      result[0] = color.r;
      result[1] = color.g;
      result[2] = color.b;
      result[3] = color.a;
      return result;
  }
  
  Value SkVMGenerator::writeIntrinsicCall(const FunctionCall& c) {
      IntrinsicKind intrinsicKind = c.function().intrinsicKind();
      SkASSERT(intrinsicKind != kNotIntrinsic);
  
      const size_t nargs = c.arguments().size();
      const size_t kMaxArgs = 3;  // eg: clamp, mix, smoothstep
      Value args[kMaxArgs];
      SkASSERT(nargs >= 1 && nargs <= SK_ARRAY_COUNT(args));
  
      // All other intrinsics have at most three args, and those can all be evaluated up front:
      for (size_t i = 0; i < nargs; ++i) {
          args[i] = this->writeExpression(*c.arguments()[i]);
      }
      Type::NumberKind nk = base_number_kind(c.arguments()[0]->type());
  
      auto binary = [&](auto&& fn) {
          // Binary intrinsics are (vecN, vecN), (vecN, float), or (float, vecN)
          size_t nslots = std::max(args[0].slots(), args[1].slots());
          Value result(nslots);
          SkASSERT(args[0].slots() == nslots || args[0].slots() == 1);
          SkASSERT(args[1].slots() == nslots || args[1].slots() == 1);
  
          for (size_t i = 0; i < nslots; ++i) {
              result[i] = fn({fBuilder, args[0][args[0].slots() == 1 ? 0 : i]},
                             {fBuilder, args[1][args[1].slots() == 1 ? 0 : i]});
          }
          return result;
      };
  
      auto ternary = [&](auto&& fn) {
          // Ternary intrinsics are some combination of vecN and float
          size_t nslots = std::max({args[0].slots(), args[1].slots(), args[2].slots()});
          Value result(nslots);
          SkASSERT(args[0].slots() == nslots || args[0].slots() == 1);
          SkASSERT(args[1].slots() == nslots || args[1].slots() == 1);
          SkASSERT(args[2].slots() == nslots || args[2].slots() == 1);
  
          for (size_t i = 0; i < nslots; ++i) {
              result[i] = fn({fBuilder, args[0][args[0].slots() == 1 ? 0 : i]},
                             {fBuilder, args[1][args[1].slots() == 1 ? 0 : i]},
                             {fBuilder, args[2][args[2].slots() == 1 ? 0 : i]});
          }
          return result;
      };
  
      auto dot = [&](const Value& x, const Value& y) {
          SkASSERT(x.slots() == y.slots());
          skvm::F32 result = f32(x[0]) * f32(y[0]);
          for (size_t i = 1; i < x.slots(); ++i) {
              result += f32(x[i]) * f32(y[i]);
          }
          return result;
      };
  
      switch (intrinsicKind) {
          case k_radians_IntrinsicKind:
              return unary(args[0], [](skvm::F32 deg) { return deg * (SK_FloatPI / 180); });
          case k_degrees_IntrinsicKind:
              return unary(args[0], [](skvm::F32 rad) { return rad * (180 / SK_FloatPI); });
  
          case k_sin_IntrinsicKind: return unary(args[0], skvm::approx_sin);
          case k_cos_IntrinsicKind: return unary(args[0], skvm::approx_cos);
          case k_tan_IntrinsicKind: return unary(args[0], skvm::approx_tan);
  
          case k_asin_IntrinsicKind: return unary(args[0], skvm::approx_asin);
          case k_acos_IntrinsicKind: return unary(args[0], skvm::approx_acos);
  
          case k_atan_IntrinsicKind: return nargs == 1 ? unary(args[0], skvm::approx_atan)
                                                   : binary(skvm::approx_atan2);
  
          case k_pow_IntrinsicKind:
              return binary([](skvm::F32 x, skvm::F32 y) { return skvm::approx_powf(x, y); });
          case k_exp_IntrinsicKind:  return unary(args[0], skvm::approx_exp);
          case k_log_IntrinsicKind:  return unary(args[0], skvm::approx_log);
          case k_exp2_IntrinsicKind: return unary(args[0], skvm::approx_pow2);
          case k_log2_IntrinsicKind: return unary(args[0], skvm::approx_log2);
  
          case k_sqrt_IntrinsicKind: return unary(args[0], skvm::sqrt);
          case k_inversesqrt_IntrinsicKind:
              return unary(args[0], [](skvm::F32 x) { return 1.0f / skvm::sqrt(x); });
  
          case k_abs_IntrinsicKind: return unary(args[0], skvm::abs);
          case k_sign_IntrinsicKind:
              return unary(args[0], [](skvm::F32 x) { return select(x < 0, -1.0f,
                                                             select(x > 0, +1.0f, 0.0f)); });
          case k_floor_IntrinsicKind: return unary(args[0], skvm::floor);
          case k_ceil_IntrinsicKind:  return unary(args[0], skvm::ceil);
          case k_fract_IntrinsicKind: return unary(args[0], skvm::fract);
          case k_mod_IntrinsicKind:
              return binary([](skvm::F32 x, skvm::F32 y) { return x - y*skvm::floor(x / y); });
  
          case k_min_IntrinsicKind:
              return binary([](skvm::F32 x, skvm::F32 y) { return skvm::min(x, y); });
          case k_max_IntrinsicKind:
              return binary([](skvm::F32 x, skvm::F32 y) { return skvm::max(x, y); });
          case k_clamp_IntrinsicKind:
              return ternary(
                      [](skvm::F32 x, skvm::F32 lo, skvm::F32 hi) { return skvm::clamp(x, lo, hi); });
          case k_saturate_IntrinsicKind:
              return unary(args[0], [](skvm::F32 x) { return skvm::clamp01(x); });
          case k_mix_IntrinsicKind:
              return ternary(
                      [](skvm::F32 x, skvm::F32 y, skvm::F32 t) { return skvm::lerp(x, y, t); });
          case k_step_IntrinsicKind:
              return binary([](skvm::F32 edge, skvm::F32 x) { return select(x < edge, 0.0f, 1.0f); });
          case k_smoothstep_IntrinsicKind:
              return ternary([](skvm::F32 edge0, skvm::F32 edge1, skvm::F32 x) {
                  skvm::F32 t = skvm::clamp01((x - edge0) / (edge1 - edge0));
                  return t ** t ** (3 - 2 ** t);
              });
  
          case k_length_IntrinsicKind: return skvm::sqrt(dot(args[0], args[0]));
          case k_distance_IntrinsicKind: {
              Value vec = binary([](skvm::F32 x, skvm::F32 y) { return x - y; });
              return skvm::sqrt(dot(vec, vec));
          }
          case k_dot_IntrinsicKind: return dot(args[0], args[1]);
          case k_cross_IntrinsicKind: {
              skvm::F32 ax = f32(args[0][0]), ay = f32(args[0][1]), az = f32(args[0][2]),
                        bx = f32(args[1][0]), by = f32(args[1][1]), bz = f32(args[1][2]);
              Value result(3);
              result[0] = ay**bz - az**by;
              result[1] = az**bx - ax**bz;
              result[2] = ax**by - ay**bx;
              return result;
          }
          case k_normalize_IntrinsicKind: {
              skvm::F32 invLen = 1.0f / skvm::sqrt(dot(args[0], args[0]));
              return unary(args[0], [&](skvm::F32 x) { return x ** invLen; });
          }
          case k_faceforward_IntrinsicKind: {
              const Value &N    = args[0],
                          &I    = args[1],
                          &Nref = args[2];
  
              skvm::F32 dotNrefI = dot(Nref, I);
              return unary(N, [&](skvm::F32 n) { return select(dotNrefI<0, n, -n); });
          }
          case k_reflect_IntrinsicKind: {
              const Value &I = args[0],
                          &N = args[1];
  
              skvm::F32 dotNI = dot(N, I);
              return binary([&](skvm::F32 i, skvm::F32 n) {
                  return i - 2**dotNI**n;
              });
          }
          case k_refract_IntrinsicKind: {
              const Value &I  = args[0],
                          &N  = args[1];
              skvm::F32   eta = f32(args[2]);
  
              skvm::F32 dotNI = dot(N, I),
                        k     = 1 - eta**eta**(1 - dotNI**dotNI);
              return binary([&](skvm::F32 i, skvm::F32 n) {
                  return select(k<0, 0.0f, eta**i - (eta**dotNI + sqrt(k))**n);
              });
          }
  
          case k_matrixCompMult_IntrinsicKind:
              return binary([](skvm::F32 x, skvm::F32 y) { return x ** y; });
          case k_inverse_IntrinsicKind: {
              switch (args[0].slots()) {
                  case  4: return this->writeMatrixInverse2x2(args[0]);
                  case  9: return this->writeMatrixInverse3x3(args[0]);
                  case 16: return this->writeMatrixInverse4x4(args[0]);
                  default:
                      SkDEBUGFAIL("Invalid call to inverse");
                      return {};
              }
          }
  
          case k_lessThan_IntrinsicKind:
              return nk == Type::NumberKind::kFloat
                             ? binary([](skvm::F32 x, skvm::F32 y) { return x < y; })
                             : binary([](skvm::I32 x, skvm::I32 y) { return x < y; });
          case k_lessThanEqual_IntrinsicKind:
              return nk == Type::NumberKind::kFloat
                             ? binary([](skvm::F32 x, skvm::F32 y) { return x <= y; })
                             : binary([](skvm::I32 x, skvm::I32 y) { return x <= y; });
          case k_greaterThan_IntrinsicKind:
              return nk == Type::NumberKind::kFloat
                             ? binary([](skvm::F32 x, skvm::F32 y) { return x > y; })
                             : binary([](skvm::I32 x, skvm::I32 y) { return x > y; });
          case k_greaterThanEqual_IntrinsicKind:
              return nk == Type::NumberKind::kFloat
                             ? binary([](skvm::F32 x, skvm::F32 y) { return x >= y; })
                             : binary([](skvm::I32 x, skvm::I32 y) { return x >= y; });
  
          case k_equal_IntrinsicKind:
              return nk == Type::NumberKind::kFloat
                             ? binary([](skvm::F32 x, skvm::F32 y) { return x == y; })
                             : binary([](skvm::I32 x, skvm::I32 y) { return x == y; });
          case k_notEqual_IntrinsicKind:
              return nk == Type::NumberKind::kFloat
                             ? binary([](skvm::F32 x, skvm::F32 y) { return x != y; })
                             : binary([](skvm::I32 x, skvm::I32 y) { return x != y; });
  
          case k_any_IntrinsicKind: {
              skvm::I32 result = i32(args[0][0]);
              for (size_t i = 1; i < args[0].slots(); ++i) {
                  result |= i32(args[0][i]);
              }
              return result;
          }
          case k_all_IntrinsicKind: {
              skvm::I32 result = i32(args[0][0]);
              for (size_t i = 1; i < args[0].slots(); ++i) {
                  result &= i32(args[0][i]);
              }
              return result;
          }
          case k_not_IntrinsicKind: return unary(args[0], [](skvm::I32 x) { return ~x; });
  
          default:
              SkDEBUGFAILF("unsupported intrinsic %s", c.function().description().c_str());
              return {};
      }
      SkUNREACHABLE;
  }
  
  Value SkVMGenerator::writeFunctionCall(const FunctionCall& f) {
      if (f.function().isIntrinsic() && !f.function().definition()) {
          return this->writeIntrinsicCall(f);
      }
  
      const FunctionDeclaration& decl = f.function();
  
      // Evaluate all arguments, gather the results into a contiguous list of IDs
      std::vector<skvm::Val> argVals;
      for (const auto& arg : f.arguments()) {
          Value v = this->writeExpression(*arg);
          for (size_t i = 0; i < v.slots(); ++i) {
              argVals.push_back(v[i]);
          }
      }
  
      // Create storage for the return value
      size_t nslots = f.type().slotCount();
      Value result(nslots);
      for (size_t i = 0; i < nslots; ++i) {
          result[i] = fBuilder->splat(0.0f);
      }
  
      {
          // This merges currentFunction().fReturned into fConditionMask. Lanes that conditionally
          // returned in the current function would otherwise resume execution within the child.
          ScopedCondition m(this, ~currentFunction().fReturned);
          SkASSERTF(f.function().definition(), "no definition for function '%s'",
                    f.function().description().c_str());
          this->writeFunction(*f.function().definition(), SkMakeSpan(argVals), result.asSpan());
      }
  
      // Propagate new values of any 'out' params back to the original arguments
      const std::unique_ptr<Expression>* argIter = f.arguments().begin();
      size_t valIdx = 0;
      for (const Variable* p : decl.parameters()) {
          nslots = p->type().slotCount();
          if (p->modifiers().fFlags & Modifiers::kOut_Flag) {
              Value v(nslots);
              for (size_t i = 0; i < nslots; ++i) {
                  v[i] = argVals[valIdx + i];
              }
              const std::unique_ptr<Expression>& arg = *argIter;
              this->writeStore(*arg, v);
          }
          valIdx += nslots;
          argIter++;
      }
  
      return result;
  }
  
  Value SkVMGenerator::writeExternalFunctionCall(const ExternalFunctionCall& c) {
      // Evaluate all arguments, gather the results into a contiguous list of F32
      std::vector<skvm::F32> args;
      for (const auto& arg : c.arguments()) {
          Value v = this->writeExpression(*arg);
          for (size_t i = 0; i < v.slots(); ++i) {
              args.push_back(f32(v[i]));
          }
      }
  
      // Create storage for the return value
      size_t nslots = c.type().slotCount();
      std::vector<skvm::F32> result(nslots, fBuilder->splat(0.0f));
  
      c.function().call(fBuilder, args.data(), result.data(), this->mask());
  
      // Convert from 'vector of F32' to Value
      Value resultVal(nslots);
      for (size_t i = 0; i < nslots; ++i) {
          resultVal[i] = result[i];
      }
  
      return resultVal;
  }
  
  Value SkVMGenerator::writePrefixExpression(const PrefixExpression& p) {
      Value val = this->writeExpression(*p.operand());
  
      switch (p.getOperator().kind()) {
          case Token::Kind::TK_PLUSPLUS:
          case Token::Kind::TK_MINUSMINUS: {
              bool incr = p.getOperator().kind() == Token::Kind::TK_PLUSPLUS;
  
              switch (base_number_kind(p.type())) {
                  case Type::NumberKind::kFloat:
                      val = f32(val) + fBuilder->splat(incr ? 1.0f : -1.0f);
                      break;
                  case Type::NumberKind::kSigned:
                      val = i32(val) + fBuilder->splat(incr ? 1 : -1);
                      break;
                  default:
                      SkASSERT(false);
                      return {};
              }
              return this->writeStore(*p.operand(), val);
          }
          case Token::Kind::TK_MINUS: {
              switch (base_number_kind(p.type())) {
                  case Type::NumberKind::kFloat:
                      return this->unary(val, [](skvm::F32 x) { return -x; });
                  case Type::NumberKind::kSigned:
                      return this->unary(val, [](skvm::I32 x) { return -x; });
                  default:
                      SkASSERT(false);
                      return {};
              }
          }
          case Token::Kind::TK_LOGICALNOT:
          case Token::Kind::TK_BITWISENOT:
              return this->unary(val, [](skvm::I32 x) { return ~x; });
          default:
              SkASSERT(false);
              return {};
      }
  }
  
  Value SkVMGenerator::writePostfixExpression(const PostfixExpression& p) {
      switch (p.getOperator().kind()) {
          case Token::Kind::TK_PLUSPLUS:
          case Token::Kind::TK_MINUSMINUS: {
              Value old = this->writeExpression(*p.operand()),
                    val = old;
              SkASSERT(val.slots() == 1);
              bool incr = p.getOperator().kind() == Token::Kind::TK_PLUSPLUS;
  
              switch (base_number_kind(p.type())) {
                  case Type::NumberKind::kFloat:
                      val = f32(val) + fBuilder->splat(incr ? 1.0f : -1.0f);
                      break;
                  case Type::NumberKind::kSigned:
                      val = i32(val) + fBuilder->splat(incr ? 1 : -1);
                      break;
                  default:
                      SkASSERT(false);
                      return {};
              }
              this->writeStore(*p.operand(), val);
              return old;
          }
          default:
              SkASSERT(false);
              return {};
      }
  }
  
  Value SkVMGenerator::writeSwizzle(const Swizzle& s) {
      Value base = this->writeExpression(*s.base());
      Value swizzled(s.components().size());
      for (size_t i = 0; i < s.components().size(); ++i) {
          swizzled[i] = base[s.components()[i]];
      }
      return swizzled;
  }
  
  Value SkVMGenerator::writeTernaryExpression(const TernaryExpression& t) {
      skvm::I32 test = i32(this->writeExpression(*t.test()));
      Value ifTrue, ifFalse;
  
      {
          ScopedCondition m(this, test);
          ifTrue = this->writeExpression(*t.ifTrue());
      }
      {
          ScopedCondition m(this, ~test);
          ifFalse = this->writeExpression(*t.ifFalse());
      }
  
      size_t nslots = ifTrue.slots();
      SkASSERT(nslots == ifFalse.slots());
  
      Value result(nslots);
      for (size_t i = 0; i < nslots; ++i) {
          result[i] = skvm::select(test, i32(ifTrue[i]), i32(ifFalse[i]));
      }
      return result;
  }
  
  Value SkVMGenerator::writeExpression(const Expression& e) {
      switch (e.kind()) {
          case Expression::Kind::kBinary:
              return this->writeBinaryExpression(e.as<BinaryExpression>());
          case Expression::Kind::kBoolLiteral:
              return fBuilder->splat(e.as<BoolLiteral>().value() ? ~0 : 0);
          case Expression::Kind::kChildCall:
              return this->writeChildCall(e.as<ChildCall>());
          case Expression::Kind::kConstructorArray:
          case Expression::Kind::kConstructorCompound:
          case Expression::Kind::kConstructorStruct:
              return this->writeAggregationConstructor(e.asAnyConstructor());
          case Expression::Kind::kConstructorArrayCast:
              return this->writeExpression(*e.as<ConstructorArrayCast>().argument());
          case Expression::Kind::kConstructorDiagonalMatrix:
              return this->writeConstructorDiagonalMatrix(e.as<ConstructorDiagonalMatrix>());
          case Expression::Kind::kConstructorMatrixResize:
              return this->writeConstructorMatrixResize(e.as<ConstructorMatrixResize>());
          case Expression::Kind::kConstructorScalarCast:
          case Expression::Kind::kConstructorCompoundCast:
              return this->writeConstructorCast(e.asAnyConstructor());
          case Expression::Kind::kConstructorSplat:
              return this->writeConstructorSplat(e.as<ConstructorSplat>());
          case Expression::Kind::kFieldAccess:
              return this->writeFieldAccess(e.as<FieldAccess>());
          case Expression::Kind::kIndex:
              return this->writeIndexExpression(e.as<IndexExpression>());
          case Expression::Kind::kVariableReference:
              return this->writeVariableExpression(e.as<VariableReference>());
          case Expression::Kind::kFloatLiteral:
              return fBuilder->splat(e.as<FloatLiteral>().value());
          case Expression::Kind::kFunctionCall:
              return this->writeFunctionCall(e.as<FunctionCall>());
          case Expression::Kind::kExternalFunctionCall:
              return this->writeExternalFunctionCall(e.as<ExternalFunctionCall>());
          case Expression::Kind::kIntLiteral:
              return fBuilder->splat(static_cast<int>(e.as<IntLiteral>().value()));
          case Expression::Kind::kPrefix:
              return this->writePrefixExpression(e.as<PrefixExpression>());
          case Expression::Kind::kPostfix:
              return this->writePostfixExpression(e.as<PostfixExpression>());
          case Expression::Kind::kSwizzle:
              return this->writeSwizzle(e.as<Swizzle>());
          case Expression::Kind::kTernary:
              return this->writeTernaryExpression(e.as<TernaryExpression>());
          case Expression::Kind::kExternalFunctionReference:
          default:
              SkDEBUGFAIL("Unsupported expression");
              return {};
      }
  }
  
  Value SkVMGenerator::writeStore(const Expression& lhs, const Value& rhs) {
      SkASSERTF(rhs.slots() == lhs.type().slotCount(),
                "lhs=%s (%s)\nrhs=%zu slot",
                lhs.type().description().c_str(), lhs.description().c_str(), rhs.slots());
  
      // We need to figure out the collection of slots that we're storing into. The l-value (lhs)
      // is always a VariableReference, possibly wrapped by one or more Swizzle, FieldAccess, or
      // IndexExpressions. The underlying VariableReference has a range of slots for its storage,
      // and each expression wrapped around that selects a sub-set of those slots (Field/Index),
      // or rearranges them (Swizzle).
      SkSTArray<4, size_t, true> slots;
      slots.resize(rhs.slots());
  
      // Start with the identity slot map - this basically says that the values from rhs belong in
      // slots [0, 1, 2 ... N] of the lhs.
      for (size_t i = 0; i < slots.size(); ++i) {
          slots[i] = i;
      }
  
      // Now, as we peel off each outer expression, adjust 'slots' to be the locations relative to
      // the next (inner) expression:
      const Expression* expr = &lhs;
      while (!expr->is<VariableReference>()) {
          switch (expr->kind()) {
              case Expression::Kind::kFieldAccess: {
                  const FieldAccess& fld = expr->as<FieldAccess>();
                  size_t offset = this->fieldSlotOffset(fld);
                  for (size_t& s : slots) {
                      s += offset;
                  }
                  expr = fld.base().get();
              } break;
              case Expression::Kind::kIndex: {
                  const IndexExpression& idx = expr->as<IndexExpression>();
                  size_t offset = this->indexSlotOffset(idx);
                  for (size_t& s : slots) {
                      s += offset;
                  }
                  expr = idx.base().get();
              } break;
              case Expression::Kind::kSwizzle: {
                  const Swizzle& swz = expr->as<Swizzle>();
                  for (size_t& s : slots) {
                      s = swz.components()[s];
                  }
                  expr = swz.base().get();
              } break;
              default:
                  // No other kinds of expressions are valid in lvalues. (see Analysis::IsAssignable)
                  SkDEBUGFAIL("Invalid expression type");
                  return {};
          }
      }
  
      // When we get here, 'slots' are all relative to the first slot holding 'var's storage
      const Variable& var = *expr->as<VariableReference>().variable();
      size_t varSlot = this->getSlot(var);
      skvm::I32 mask = this->mask();
      for (size_t i = rhs.slots(); i --> 0;) {
          SkASSERT(slots[i] < var.type().slotCount());
          skvm::F32 curr = f32(fSlots[varSlot + slots[i]]),
                    next = f32(rhs[i]);
          fSlots[varSlot + slots[i]] = select(mask, next, curr).id;
      }
      return rhs;
  }
  
  void SkVMGenerator::writeBlock(const Block& b) {
      for (const std::unique_ptr<Statement>& stmt : b.children()) {
          this->writeStatement(*stmt);
      }
  }
  
  void SkVMGenerator::writeBreakStatement() {
      // Any active lanes stop executing for the duration of the current loop
      fLoopMask &= ~this->mask();
  }
  
  void SkVMGenerator::writeContinueStatement() {
      // Any active lanes stop executing for the current iteration.
      // Remember them in fContinueMask, to be re-enabled later.
      skvm::I32 mask = this->mask();
      fLoopMask &= ~mask;
      fContinueMask |= mask;
  }
  
  void SkVMGenerator::writeForStatement(const ForStatement& f) {
      // We require that all loops be ES2-compliant (unrollable), and actually unroll them here
      Analysis::UnrollableLoopInfo loop;
      SkAssertResult(Analysis::ForLoopIsValidForES2(f.fOffset, f.initializer().get(), f.test().get(),
                                                    f.next().get(), f.statement().get(), &loop,
                                                    /*errors=*/nullptr));
      SkASSERT(loop.fIndex->type().slotCount() == 1);
  
      size_t indexSlot = this->getSlot(*loop.fIndex);
      double val = loop.fStart;
  
      skvm::I32 oldLoopMask     = fLoopMask,
                oldContinueMask = fContinueMask;
  
      for (int i = 0; i < loop.fCount; ++i) {
          fSlots[indexSlot] = loop.fIndex->type().isInteger()
                                      ? fBuilder->splat(static_cast<int>(val)).id
                                      : fBuilder->splat(static_cast<float>(val)).id;
  
          fContinueMask = fBuilder->splat(0);
          this->writeStatement(*f.statement());
          fLoopMask |= fContinueMask;
  
          val += loop.fDelta;
      }
  
      fLoopMask     = oldLoopMask;
      fContinueMask = oldContinueMask;
  }
  
  void SkVMGenerator::writeIfStatement(const IfStatement& i) {
      Value test = this->writeExpression(*i.test());
      {
          ScopedCondition ifTrue(this, i32(test));
          this->writeStatement(*i.ifTrue());
      }
      if (i.ifFalse()) {
          ScopedCondition ifFalse(this, ~i32(test));
          this->writeStatement(*i.ifFalse());
      }
  }
  
  void SkVMGenerator::writeReturnStatement(const ReturnStatement& r) {
      skvm::I32 returnsHere = this->mask();
  
      if (r.expression()) {
          Value val = this->writeExpression(*r.expression());
  
          int i = 0;
          for (skvm::Val& slot : currentFunction().fReturnValue) {
              slot = select(returnsHere, f32(val[i]), f32(slot)).id;
              i++;
          }
      }
  
      currentFunction().fReturned |= returnsHere;
  }
  
  void SkVMGenerator::writeVarDeclaration(const VarDeclaration& decl) {
      size_t slot   = this->getSlot(decl.var()),
             nslots = decl.var().type().slotCount();
  
      Value val = decl.value() ? this->writeExpression(*decl.value()) : Value{};
      for (size_t i = 0; i < nslots; ++i) {
          fSlots[slot + i] = val ? val[i] : fBuilder->splat(0.0f).id;
      }
  }
  
  void SkVMGenerator::writeStatement(const Statement& s) {
      switch (s.kind()) {
          case Statement::Kind::kBlock:
              this->writeBlock(s.as<Block>());
              break;
          case Statement::Kind::kBreak:
              this->writeBreakStatement();
              break;
          case Statement::Kind::kContinue:
              this->writeContinueStatement();
              break;
          case Statement::Kind::kExpression:
              this->writeExpression(*s.as<ExpressionStatement>().expression());
              break;
          case Statement::Kind::kFor:
              this->writeForStatement(s.as<ForStatement>());
              break;
          case Statement::Kind::kIf:
              this->writeIfStatement(s.as<IfStatement>());
              break;
          case Statement::Kind::kReturn:
              this->writeReturnStatement(s.as<ReturnStatement>());
              break;
          case Statement::Kind::kVarDeclaration:
              this->writeVarDeclaration(s.as<VarDeclaration>());
              break;
          case Statement::Kind::kDiscard:
          case Statement::Kind::kDo:
          case Statement::Kind::kSwitch:
              SkDEBUGFAIL("Unsupported control flow");
              break;
          case Statement::Kind::kInlineMarker:
          case Statement::Kind::kNop:
              break;
          default:
              SkASSERT(false);
      }
  }
  
  skvm::Color ProgramToSkVM(const Program& program,
                            const FunctionDefinition& function,
                            skvm::Builder* builder,
                            SkSpan<skvm::Val> uniforms,
                            skvm::Coord device,
                            skvm::Coord local,
                            skvm::Color inputColor,
                            skvm::Color destColor,
                            SampleShaderFn sampleShader,
                            SampleColorFilterFn sampleColorFilter,
                            SampleBlenderFn sampleBlender) {
      skvm::Val zero = builder->splat(0.0f).id;
      skvm::Val result[4] = {zero,zero,zero,zero};
  
      skvm::Val args[8];  // At most 8 arguments (half4 srcColor, half4 dstColor)
      size_t argSlots = 0;
      for (const SkSL::Variable* param : function.declaration().parameters()) {
          switch (param->modifiers().fLayout.fBuiltin) {
              case SK_MAIN_COORDS_BUILTIN:
                  SkASSERT(param->type().slotCount() == 2);
                  SkASSERT((argSlots + 2) <= SK_ARRAY_COUNT(args));
                  args[argSlots++] = local.x.id;
                  args[argSlots++] = local.y.id;
                  break;
              case SK_INPUT_COLOR_BUILTIN:
                  SkASSERT(param->type().slotCount() == 4);
                  SkASSERT((argSlots + 4) <= SK_ARRAY_COUNT(args));
                  args[argSlots++] = inputColor.r.id;
                  args[argSlots++] = inputColor.g.id;
                  args[argSlots++] = inputColor.b.id;
                  args[argSlots++] = inputColor.a.id;
                  break;
              case SK_DEST_COLOR_BUILTIN:
                  SkASSERT(param->type().slotCount() == 4);
                  SkASSERT((argSlots + 4) <= SK_ARRAY_COUNT(args));
                  args[argSlots++] = destColor.r.id;
                  args[argSlots++] = destColor.g.id;
                  args[argSlots++] = destColor.b.id;
                  args[argSlots++] = destColor.a.id;
                  break;
              default:
                  SkDEBUGFAIL("Invalid parameter to main()");
                  return {};
          }
      }
      SkASSERT(argSlots <= SK_ARRAY_COUNT(args));
  
      SkVMGenerator generator(program, builder, uniforms, device, local, std::move(sampleShader),
                              std::move(sampleColorFilter), std::move(sampleBlender));
      generator.writeFunction(function, {args, argSlots}, SkMakeSpan(result));
  
      return skvm::Color{{builder, result[0]},
                         {builder, result[1]},
                         {builder, result[2]},
                         {builder, result[3]}};
  }
  
  bool ProgramToSkVM(const Program& program,
                     const FunctionDefinition& function,
                     skvm::Builder* b,
                     SkSpan<skvm::Val> uniforms,
                     SkVMSignature* outSignature) {
      SkVMSignature ignored,
                    *signature = outSignature ? outSignature : &ignored;
  
      std::vector<skvm::Ptr> argPtrs;
      std::vector<skvm::Val> argVals;
  
      for (const Variable* p : function.declaration().parameters()) {
          size_t slots = p->type().slotCount();
          signature->fParameterSlots += slots;
          for (size_t i = 0; i < slots; ++i) {
              argPtrs.push_back(b->varying<float>());
              argVals.push_back(b->loadF(argPtrs.back()).id);
          }
      }
  
      std::vector<skvm::Ptr> returnPtrs;
      std::vector<skvm::Val> returnVals;
  
      signature->fReturnSlots = function.declaration().returnType().slotCount();
      for (size_t i = 0; i < signature->fReturnSlots; ++i) {
          returnPtrs.push_back(b->varying<float>());
          returnVals.push_back(b->splat(0.0f).id);
      }
  
      skvm::F32 zero = b->splat(0.0f);
      skvm::Coord zeroCoord = {zero, zero};
      SkVMGenerator generator(program, b, uniforms, /*device=*/zeroCoord, /*local=*/zeroCoord,
                              /*sampleShader=*/nullptr, /*sampleColorFilter=*/nullptr,
                              /*sampleBlender=*/nullptr);
      generator.writeFunction(function, SkMakeSpan(argVals), SkMakeSpan(returnVals));
  
      // generateCode has updated the contents of 'argVals' for any 'out' or 'inout' parameters.
      // Propagate those changes back to our varying buffers:
      size_t argIdx = 0;
      for (const Variable* p : function.declaration().parameters()) {
          size_t nslots = p->type().slotCount();
          if (p->modifiers().fFlags & Modifiers::kOut_Flag) {
              for (size_t i = 0; i < nslots; ++i) {
                  b->storeF(argPtrs[argIdx + i], skvm::F32{b, argVals[argIdx + i]});
              }
          }
          argIdx += nslots;
      }
  
      // It's also updated the contents of 'returnVals' with the return value of the entry point.
      // Store that as well:
      for (size_t i = 0; i < signature->fReturnSlots; ++i) {
          b->storeF(returnPtrs[i], skvm::F32{b, returnVals[i]});
      }
  
      return true;
  }
  
  const FunctionDefinition* Program_GetFunction(const Program& program, const char* function) {
      for (const ProgramElement* e : program.elements()) {
          if (e->is<FunctionDefinition>() &&
              e->as<FunctionDefinition>().declaration().name() == function) {
              return &e->as<FunctionDefinition>();
          }
      }
      return nullptr;
  }
  
  static void gather_uniforms(UniformInfo* info, const Type& type, const String& name) {
      switch (type.typeKind()) {
          case Type::TypeKind::kStruct:
              for (const auto& f : type.fields()) {
                  gather_uniforms(info, *f.fType, name + "." + f.fName);
              }
              break;
          case Type::TypeKind::kArray:
              for (int i = 0; i < type.columns(); ++i) {
                  gather_uniforms(info, type.componentType(),
                                  String::printf("%s[%d]", name.c_str(), i));
              }
              break;
          case Type::TypeKind::kScalar:
          case Type::TypeKind::kVector:
          case Type::TypeKind::kMatrix:
              info->fUniforms.push_back({name, base_number_kind(type), type.rows(), type.columns(),
                                         info->fUniformSlotCount});
              info->fUniformSlotCount += type.columns() * type.rows();
              break;
          default:
              break;
      }
  }
  
  std::unique_ptr<UniformInfo> Program_GetUniformInfo(const Program& program) {
      auto info = std::make_unique<UniformInfo>();
      for (const ProgramElement* e : program.elements()) {
          if (!e->is<GlobalVarDeclaration>()) {
              continue;
          }
          const GlobalVarDeclaration& decl = e->as<GlobalVarDeclaration>();
          const Variable& var = decl.declaration()->as<VarDeclaration>().var();
          if (var.modifiers().fFlags & Modifiers::kUniform_Flag) {
              gather_uniforms(info.get(), var.type(), String(var.name()));
          }
      }
      return info;
  }
  
  /*
   * Testing utility function that emits program's "main" with a minimal harness. Used to create
   * representative skvm op sequences for SkSL tests.
   */
  bool testingOnly_ProgramToSkVMShader(const Program& program, skvm::Builder* builder) {
      const SkSL::FunctionDefinition* main = Program_GetFunction(program, "main");
      if (!main) {
          return false;
      }
  
      size_t uniformSlots = 0;
      int childSlots = 0;
      for (const SkSL::ProgramElement* e : program.elements()) {
          if (e->is<GlobalVarDeclaration>()) {
              const GlobalVarDeclaration& decl = e->as<GlobalVarDeclaration>();
              const Variable& var = decl.declaration()->as<VarDeclaration>().var();
              if (var.type().isEffectChild()) {
                  childSlots++;
              } else if (is_uniform(var)) {
                  uniformSlots += var.type().slotCount();
              }
          }
      }
  
      skvm::Uniforms uniforms(builder->uniform(), 0);
  
      auto new_uni = [&]() { return builder->uniformF(uniforms.pushF(0.0f)); };
  
      // Assume identity CTM
      skvm::Coord device = {pun_to_F32(builder->index()), new_uni()};
      skvm::Coord local  = device;
  
      struct Child {
          skvm::Uniform addr;
          skvm::I32     rowBytesAsPixels;
      };
  
      std::vector<Child> children;
      for (int i = 0; i < childSlots; ++i) {
          children.push_back({uniforms.pushPtr(nullptr), builder->uniform32(uniforms.push(0))});
      }
  
      auto sampleShader = [&](int i, skvm::Coord coord) {
          skvm::PixelFormat pixelFormat = skvm::SkColorType_to_PixelFormat(kRGBA_F32_SkColorType);
          skvm::I32 index  = trunc(coord.x);
                    index += trunc(coord.y) * children[i].rowBytesAsPixels;
          return gather(pixelFormat, children[i].addr, index);
      };
  
      std::vector<skvm::Val> uniformVals;
      for (size_t i = 0; i < uniformSlots; ++i) {
          uniformVals.push_back(new_uni().id);
      }
  
      skvm::Color inColor = builder->uniformColor(SkColors::kWhite, &uniforms);
      skvm::Color destColor = builder->uniformColor(SkColors::kBlack, &uniforms);
  
      skvm::Color result = SkSL::ProgramToSkVM(program, *main, builder, SkMakeSpan(uniformVals),
                                               device, local, inColor, destColor, sampleShader,
                                               /*sampleColorFilter=*/nullptr,
                                               /*sampleBlender=*/nullptr);
  
      storeF(builder->varying<float>(), result.r);
      storeF(builder->varying<float>(), result.g);
      storeF(builder->varying<float>(), result.b);
      storeF(builder->varying<float>(), result.a);
  
      return true;
  
  }
  
  }  // namespace SkSL
  