8. The method according to claim 7 , wherein converting the non-BCD operation in the first compiler expression to the BCD operation is performed if any of following conditions is satisfied: (1) if the non-BCD operation is a logical sum operation of constant values for a byte-length operand; a definition (def) for a use (use) of the byte-length operand uniquely exists, and the definition (def) is a packed decimal operand or a zoned decimal operand; an address of the use (use) of the byte-length operand is the same as a right-end address of the definition (def) for the use (use), and a value expressed as a constant in the first compiler expression is a value which causes only all bits of sign parts to be 1; (2) if the non-BCD operation is a logical product operation of constant values for a byte-length operand; a definition (def) for use (use) of the byte-length operand uniquely exists, and the definition (def) is a packed decimal operand; an address of the use (use) of the byte-length operand is different from a right-end address of the definition (def) for the use (use), and a value expressed as a constant in the first compiler expression is a value which causes high order digits to be zero; (3) if the non-BCD operation is a memory comparison operation; in the use-definition and/or definition-use chains of a first operand for memory comparison in the first compiler expression, there is a definition (def) dominating a use (use) of the first operand, there is not another definition (def) for the use (use) in any of paths between the definition (def) and the use (use), and the use (use) exists for the definition (def) as only one use; a right-end address of the use (use) of the first operand is the same as a right-end address of the definition (def) of the first operand; the definition (def) of the first operand is a packed decimal operand; a size of the use (use) of the first operand is the same as a size of the definition (def) of the first operand, or the size of the use (use) of the first operand is smaller than the size of the definition (def) of the first operand, or the size of the use (use) of the first operand is larger than the size of the definition (def) of the first operand and zero is put in an area where the use (use) of the first operand and the definition (def) of the first operand do not overlap; in the use-definition and/or definition-use chains of a second operand for memory comparison in the first compiler expression, there is a definition (def) dominating a use (use) of the second operand, there is not another definition (def) for the use (use) in any of paths between the definition (def) and the use (use), and the use (use) exists for the definition (def) as only one use; a right-end address of the use (use) of the second operand is the same as a right-end address of the definition (def) of the second operand; the definition (def) of the second operand is a packed decimal operand; and a size of the use (use) of the second operand is the same as a size of the definition (def) of the second operand, or the size of the use (use) of the second operand is smaller than the size of the definition (def) of the second operand, or the size of the use (use) of the second operand is larger than the size of the definition (def) of the second operand and zero is put in an area where the use (use) of the second operand and the definition (def) of the second operand do not overlap; or (4) if the non-BCD operation is a memory copy operation; in the use-definition and/or definition-use chains of a memory copy source operand in the first compiler expression, there is a use (use) dominated by a definition (def), there is not another definition (def) for the use (use) in any of paths between the definition (def) and the use (use), and the use (use) exists for the definition (def) as only one use; a right-end address of the use (use) of the memory copy source operand is the same as a right-end address of the definition (def) of the memory copy source operand; the definition (def) of the memory copy source is a packed decimal operand; and a size of the use (use) of the memory copy source operand is the same as a size of the definition (def) of the memory copy source operand, or the size of the use (use) of the memory copy source operand is smaller than the size of the definition (def) of the memory copy source operand, or the size of the use (use) of the memory copy source operand is larger than the size of the definition (def) of the memory copy source operand and zero is put in an area where the use (use) of the memory copy source operand and the definition (def) of the memory copy source operand do not overlap.
7. The method according to claim 1 , further comprising converting a non-BCD operation in the first compiler expression to the BCD operation.