[llvm] [InstCombine] Fix profile metadata when folding implied conditionals (PR #170756)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Aiden Grossman (boomanaiden154)

<details>
<summary>Changes</summary>

\#<!-- -->163412 touched this last and directly propagated the profile information. This was not correct for the motivating example:

  %a = icmp eq i32 %z, 0
  %b = icmp eq i32 %z, 1
  %v2 = select i1 %b, i1 true, i1 %pred, !prof !18
  %v3 = and i1 %a, %v2

to

  %a = icmp eq i32 %z, 0
  %v3 = select i1 %a, i1 %pred, i1 false

z == 1 does not imply that z == 0 for i8. In general for the and case, we need a => b, which means that b must be equivalent or more restrictive than a, which means we cannot propagate profile information without additional information on the value distribution of z. For the or case we need !a => b. We again cannot derive profile information for a/!a without additional value distribution information.

---
Full diff: https://github.com/llvm/llvm-project/pull/170756.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (+3-7) 
- (modified) llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index c9f51e4b294b1..c00551bc1f939 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -3067,14 +3067,10 @@ Instruction *InstCombinerImpl::foldAndOrOfSelectUsingImpliedCond(Value *Op,
          "Op must be either i1 or vector of i1.");
   if (SI.getCondition()->getType() != Op->getType())
     return nullptr;
-  if (Value *V = simplifyNestedSelectsUsingImpliedCond(SI, Op, IsAnd, DL)) {
-    Instruction *MDFrom = nullptr;
-    if (!ProfcheckDisableMetadataFixes)
-      MDFrom = &SI;
-    return SelectInst::Create(
+  if (Value *V = simplifyNestedSelectsUsingImpliedCond(SI, Op, IsAnd, DL))
+    return createSelectInstWithUnknownProfile(
         Op, IsAnd ? V : ConstantInt::getTrue(Op->getType()),
-        IsAnd ? ConstantInt::getFalse(Op->getType()) : V, "", nullptr, MDFrom);
-  }
+        IsAnd ? ConstantInt::getFalse(Op->getType()) : V);
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll b/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll
index bc988a9bbab04..d783cbf25de28 100644
--- a/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll
+++ b/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll
@@ -263,5 +263,5 @@ define i1 @neg_icmp_eq_implies_trunc(i8 %x, i1 %c) {
 !1 = !{!"branch_weights", i32 2, i32 3}
 ;.
 ; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000}
-; CHECK: [[PROF1]] = !{!"branch_weights", i32 2, i32 3}
+; CHECK: [[PROF1]] = !{!"unknown", !"instcombine"}
 ;.

``````````

</details>


https://github.com/llvm/llvm-project/pull/170756