<p dir="auto">An overflowing fp -&gt; int cast, for example:</p>
<div class="highlight highlight-source-rust notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="#[inline(never)]
fn show&lt;T: std::fmt::Debug&gt;(e: T) { println!(&quot;{:?}&quot;, e) }

fn main() {
    show({
        9.223372036854776e18f64 as i64
    });
}"><pre class="notranslate"><span class="pl-c1">#<span class="pl-kos">[</span>inline<span class="pl-kos">(</span>never<span class="pl-kos">)</span><span class="pl-kos">]</span></span>
<span class="pl-k">fn</span> <span class="pl-en">show</span><span class="pl-kos">&lt;</span><span class="pl-smi">T</span><span class="pl-kos">:</span> std<span class="pl-kos">::</span>fmt<span class="pl-kos">::</span><span class="pl-smi">Debug</span><span class="pl-kos">&gt;</span><span class="pl-kos">(</span><span class="pl-s1">e</span><span class="pl-kos">:</span> <span class="pl-smi">T</span><span class="pl-kos">)</span> <span class="pl-kos">{</span> <span class="pl-en">println</span><span class="pl-en">!</span><span class="pl-kos">(</span><span class="pl-s">"{:?}"</span>, e<span class="pl-kos">)</span> <span class="pl-kos">}</span>

<span class="pl-k">fn</span> <span class="pl-en">main</span><span class="pl-kos">(</span><span class="pl-kos">)</span> <span class="pl-kos">{</span>
    <span class="pl-en">show</span><span class="pl-kos">(</span><span class="pl-kos">{</span>
        <span class="pl-c1">9.223372036854776e18f64</span> <span class="pl-k">as</span> <span class="pl-smi">i64</span>
    <span class="pl-kos">}</span><span class="pl-kos">)</span><span class="pl-kos">;</span>
<span class="pl-kos">}</span></pre></div>
<p dir="auto"><a href="http://is.gd/0sDILD" rel="nofollow">playpen</a></p>
<p dir="auto">Causes LLVM to not initialise the parameter passed to <code class="notranslate">show</code>:</p>
<div class="highlight highlight-source-llvm notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="trs: uwtable
define internal void @_ZN4main20he0a80c27bce3fc14RaaE() unnamed_addr #0 {
entry-block:
  tail call fastcc void @_ZN4show21h11375292364260386722E()
  ret void
}"><pre class="notranslate">trs: <span class="pl-k">uwtable</span>
<span class="pl-k">define</span> <span class="pl-k">internal</span> <span class="pl-k">void</span> <span class="pl-c1">@_ZN4main20he0a80c27bce3fc14RaaE</span>() <span class="pl-k">unnamed_addr</span> #<span class="pl-c1">0</span> {
entry-block:
  <span class="pl-k">tail</span> <span class="pl-k">call</span> <span class="pl-k">fastcc</span> <span class="pl-k">void</span> <span class="pl-c1">@_ZN4show21h11375292364260386722E</span>()
  <span class="pl-k">ret</span> <span class="pl-k">void</span>
}</pre></div>
<blockquote>
<p dir="auto">If the value cannot fit within the destination type, ty2, then the results are undefined.</p>
</blockquote>
<p dir="auto"><a href="http://llvm.org/docs/LangRef.html#fptrunc-to-instruction" rel="nofollow">http://llvm.org/docs/LangRef.html#fptrunc-to-instruction</a></p>
<p dir="auto">e.g. <code class="notranslate">1e300f64 as f32</code></p>
<p dir="auto">cc <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="21869137" data-permission-text="Title is private" data-url="https://github.com/rust-lang/rust/issues/10184" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/10184/hovercard" href="https://github.com/rust-lang/rust/issues/10184">#10184</a>, <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="21869206" data-permission-text="Title is private" data-url="https://github.com/rust-lang/rust/issues/10185" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/10185/hovercard" href="https://github.com/rust-lang/rust/issues/10185">#10185</a></p>