[InstCombine] Mark as unknown the branch weights of packed integer selecting shifts

[mtrofin]

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

[mtrofin]

• [InstCombine] Mark as unknown the branch weights of packed integer selecting shifts #162726 👈 (View in Graphite)
• [NFC][InstCombine] Make use of unknown profile info clear in the API name #162766
• main

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Mircea Trofin (mtrofin)

Changes

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 --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;
 }

[boomanaiden154]

LGTM. No existing data to pull from, and there's no way to have a reasonable guess about which why the select goes without instrumentation.

[nikic]

Can we use

llvm-project/llvm/lib/Transforms/InstCombine/InstCombineInternal.h

Line 473 in 6fe878a

SelectInst *createSelectInst(Value *C, Value *S1, Value *S2,

here instead?

[mtrofin]

yup - just had to make it public (plus the change before in the stack)

[mtrofin]

Merge activity

• Oct 10, 5:28 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Oct 10, 5:30 PM UTC: @mtrofin merged this pull request with Graphite.