[llvm] [InstCombine] optimize powi(X,Y)/X with Ofast (PR #67236)

[Nikita Popov via llvm-commits]

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@@ -1764,6 +1764,19 @@ Instruction *InstCombinerImpl::visitFDiv(BinaryOperator &I) {
     return replaceInstUsesWith(I, Pow);
   }
 
+  // powi(X, Y) / X --> powi(X, Y-1)
+  // Todo: Multi-use may be also better off creating Powi(x,y-1)
+  if (I.hasNoInfs() && I.isFast() &&
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nikic wrote:

No, you should check specific flags liked at https://llvm.org/docs/LangRef.html#fast-math-flags, not the aggregate `fast` flag.

https://github.com/llvm/llvm-project/pull/67236