[llvm] [InstCombine] Fold tan(x) * cos(x) => sin(x) (PR #136319)

[Matt Arsenault via llvm-commits]

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@@ -947,6 +947,14 @@ Instruction *InstCombinerImpl::foldFMulReassoc(BinaryOperator &I) {
     return BinaryOperator::CreateFMulFMF(XX, Y, &I);
   }
 
+  // tan(X) * cos(X) -> sin(X)
+  if (match(&I,
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arsenm wrote:

> What you are suggesting here is, IMO, a significant extension to the way the contract flag is interpreted

It's how the contract flag is already interpreted, see https://discourse.llvm.org/t/rfc-fast-math-flags-semantics-contract/84478

https://github.com/llvm/llvm-project/pull/136319