[llvm] [InstCombine] Fold fast powi(2.0, x) to ldexp(1.0, x) (PR #202114)

[via llvm-commits]

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@@ -2518,7 +2518,18 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
           return replaceOperand(*II, 0, X);
       }
     }
+    if (ConstantFP *Base = dyn_cast<ConstantFP>(II->getArgOperand(0))) {
+      Value *Exp = II->getArgOperand(1);
+      // powi(2.0, p) -> ldexp(1.0, p)
+      if (Base->isExactlyValue(2.f) && II->isFast()) {
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Andarwinux wrote:

Isn't requiring IsFast too strict? I think approxFunc is enough.

https://github.com/llvm/llvm-project/pull/202114