SimplifyLibCalls: Prefer to emit intrinsic in pow(2, x) -> ldexp(1, x) (#92363)

Author: arsenm

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -2092,11 +2092,19 @@ Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilderBase &B) {
   if (!Ty->isVectorTy() && match(Base, m_SpecificFP(2.0)) &&
       (isa<SIToFPInst>(Expo) || isa<UIToFPInst>(Expo)) &&
       hasFloatFn(M, TLI, Ty, LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl)) {
-    if (Value *ExpoI = getIntToFPVal(Expo, B, TLI->getIntSize()))
-      return copyFlags(*Pow,
-                       emitBinaryFloatFnCall(ConstantFP::get(Ty, 1.0), ExpoI,
-                                             TLI, LibFunc_ldexp, LibFunc_ldexpf,
-                                             LibFunc_ldexpl, B, NoAttrs));
+    if (Value *ExpoI = getIntToFPVal(Expo, B, TLI->getIntSize())) {
+      Constant *One = ConstantFP::get(Ty, 1.0);
+
+      if (Pow->doesNotAccessMemory()) {
+        return copyFlags(*Pow, B.CreateIntrinsic(Intrinsic::ldexp,
+                                                 {Ty, ExpoI->getType()},
+                                                 {One, ExpoI}, Pow, "exp2"));
+      }
+
+      return copyFlags(*Pow, emitBinaryFloatFnCall(
+                                 One, ExpoI, TLI, LibFunc_ldexp, LibFunc_ldexpf,
+                                 LibFunc_ldexpl, B, NoAttrs));
+    }
   }
 
   // pow(2.0 ** n, x) -> exp2(n * x)