[llvm] [InstCombine] Fix ProfCheck for optimizing bitreverse (PR #227189)

[Aiden Grossman via llvm-commits]

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@@ -2556,8 +2557,15 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         X->getType()->isIntOrIntVectorTy(1)) {
       Type *Ty = II->getType();
       APInt SignBit = APInt::getSignMask(Ty->getScalarSizeInBits());
-      return SelectInst::Create(X, ConstantInt::get(Ty, SignBit),
-                                ConstantInt::getNullValue(Ty));
+      SelectInst *SI = SelectInst::Create(X, ConstantInt::get(Ty, SignBit),
+                                          ConstantInt::getNullValue(Ty));
+      // Mark the branch weights explicitly unknown as in the general case we
+      // cannot infer the probability of the condition without additional value
+      // profiling.
+      if (std::optional<uint64_t> EC = F.getEntryCount(); !EC || *EC == 0)
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boomanaiden154 wrote:

We do, but it looks at the function attached to the instruction. Given we've used SelectInst::Create, it's not attached to a function yet, so using the default helper function causes a null pointer dereference.

https://github.com/llvm/llvm-project/pull/227189