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

[Mircea Trofin via llvm-branch-commits]

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

>From ac32705be2484dee3256cfbe33ab7746d6f900d7 Mon Sep 17 00:00:00 2001
From: Mircea Trofin <mtrofin at google.com>
Date: Thu, 9 Oct 2025 12:57:39 -0700
Subject: [PATCH] [InstCombine] Mark as unknown the branch weights of packed
 integer selecting shifts

---
 llvm/lib/Transforms/InstCombine/InstCombineInternal.h       | 2 +-
 .../Transforms/InstCombine/InstCombineSimplifyDemanded.cpp  | 6 +++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 71f96f37832b3..03153971b343b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -470,6 +470,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   Value *simplifyNonNullOperand(Value *V, bool HasDereferenceable,
                                 unsigned Depth = 0);
 
+public:
   /// Create `select C, S1, S2` and copy metadata from MDFrom.
   SelectInst *createSelectInst(Value *C, Value *S1, Value *S2,
                                const Instruction &MDFrom,
@@ -490,7 +491,6 @@ 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;
 }