[llvm] 01e19e8 - [InstCombine] Mark as unknown the branch weights of packed integer selecting shifts (#162726)

[via llvm-commits]

Author: Mircea Trofin
Date: 2025-10-10T10:30:30-07:00
New Revision: 01e19e850ff40c2642da811c4dde58f323b1af1a

URL: https://github.com/llvm/llvm-project/commit/01e19e850ff40c2642da811c4dde58f323b1af1a
DIFF: https://github.com/llvm/llvm-project/commit/01e19e850ff40c2642da811c4dde58f323b1af1a.diff

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

Follow up from PR #162147. We do not have existing !prof metadata to synthesize one for the new `select`​ .

Fixes https://lab.llvm.org/staging/#/builders/221/builds/3091

Issue #147390

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineInternal.h
    llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 943c223e516fb..70718766e8ec5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -471,6 +471,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   Value *simplifyNonNullOperand(Value *V, bool HasDereferenceable,
                                 unsigned Depth = 0);
 
+public:
   /// Create `select C, S1, S2`. Use only when the profile cannot be calculated
   /// from existing profile metadata: if the Function has profiles, this will
   /// set the profile of this select to "unknown".
@@ -483,7 +484,6 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
     return Sel;
   }
 
-public:
   /// Create and insert the idiom we use to indicate a block is unreachable
   /// without having to rewrite the CFG from within InstCombine.
   void CreateNonTerminatorUnreachable(Instruction *InsertAt) {

diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 127a506e440b7..63e24a0e90853 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"
 
@@ -107,7 +108,10 @@ static Value *simplifyShiftSelectingPackedElement(Instruction *I,
   Value *ShrAmtZ =
       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.
+  Value *Select = IC.createSelectInstWithUnknownProfile(ShrAmtZ, Lower, Upper);
+  IC.Builder.Insert(Select);
   Select->takeName(I);
   return Select;
 }