[llvm] [SimplifyLibCalls] Merge sqrt into the power of exp (PR #79146)

[Anton Sidorenko via llvm-commits]

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@@ -2538,6 +2538,70 @@ Value *LibCallSimplifier::optimizeLog(CallInst *Log, IRBuilderBase &B) {
   return Ret;
 }
 
+// sqrt(exp(X)) -> exp(X * 0.5)
+Value *LibCallSimplifier::mergeSqrtToExp(CallInst *CI, IRBuilderBase &B) {
+  if (!CI->isFast())
+    return nullptr;
+
+  Function *SqrtFn = CI->getCalledFunction();
+  CallInst *Arg = dyn_cast<CallInst>(CI->getArgOperand(0));
+  if (!Arg || !Arg->isFast() || !Arg->hasOneUse())
+    return nullptr;
+  Intrinsic::ID ArgID = Arg->getIntrinsicID();
+  LibFunc ArgLb = NotLibFunc;
+  TLI->getLibFunc(*Arg, ArgLb);
+
+  LibFunc SqrtLb, ExpLb, Exp2Lb, Exp10Lb;
+
+  if (TLI->getLibFunc(SqrtFn->getName(), SqrtLb))
+    switch (SqrtLb) {
+    case LibFunc_sqrtf:
+      ExpLb = LibFunc_expf;
+      Exp2Lb = LibFunc_exp2f;
+      Exp10Lb = LibFunc_exp10f;
+      break;
+    case LibFunc_sqrt:
+      ExpLb = LibFunc_exp;
+      Exp2Lb = LibFunc_exp2;
+      Exp10Lb = LibFunc_exp10;
+      break;
+    case LibFunc_sqrtl:
+      ExpLb = LibFunc_expl;
+      Exp2Lb = LibFunc_exp2l;
+      Exp10Lb = LibFunc_exp10l;
+      break;
+    default:
+      return nullptr;
+    }
+  else if (SqrtFn->getIntrinsicID() == Intrinsic::sqrt) {
----------------
asi-sc wrote:

I couldn't find any other approaches to this. All code in this file seems to be written in the same way. 

https://github.com/llvm/llvm-project/pull/79146