[llvm] [InstCombine] Mark as unknown the branch weights of packed integer selecting shifts (PR #162726)

[Aiden Grossman via llvm-commits]

================
@@ -108,6 +109,11 @@ static Value *simplifyShiftSelectingPackedElement(Instruction *I,
       IC.Builder.CreateICmpEQ(ShrAmt, Constant::getNullValue(ShrAmt->getType()),
                               ShrAmt->getName() + ".z");
   Value *Select = IC.Builder.CreateSelect(ShrAmtZ, Lower, Upper);
+  // There is no existing !prof metadata we can derive the !prof metadata for
+  // this select.
+  if (auto *SI = dyn_cast<SelectInst>(Select))
----------------
boomanaiden154 wrote:

Ah, yep. Looks like `InstCombine` uses the `TargetFolder` which will constant fold selects that are constant.

Thanks for pointing that out.

https://github.com/llvm/llvm-project/pull/162726