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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Mircea Trofin (mtrofin)

<details>
<summary>Changes</summary>

Follow up from PR #<!-- -->162147. 

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


1 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp (+6) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 127a506e440b7..eb03f16e89e03 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -16,6 +16,7 @@
 #include "llvm/IR/GetElementPtrTypeIterator.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/ProfDataUtils.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/InstCombine/InstCombiner.h"
 
@@ -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))
+    setExplicitlyUnknownBranchWeightsIfProfiled(
+        *SI, *SI->getParent()->getParent(), DEBUG_TYPE);
   Select->takeName(I);
   return Select;
 }

``````````

</details>


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