[llvm] [SimplifyCFG] Don't propagate weights to unconditional branches in `turnSwitchRangeIntoICmp` (PR #165931)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Mircea Trofin (mtrofin)

<details>
<summary>Changes</summary>

PR #<!-- -->161000 introduced a bug whereby the IR would become invalid by having an unconditional branch have `!prof`​attached to it. This only became evident in PR #<!-- -->165744, because the IR of `test/Transforms/SimplifyCFG/pr165301.ll`​was simple enough to both (1) introduce the unconditional branch, and (2) survive in that fashion until the end of the pass (simplifycfg) and thus trip the verifier.

---
Full diff: https://github.com/llvm/llvm-project/pull/165931.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+1-1) 
- (modified) llvm/test/Transforms/SimplifyCFG/pr165301.ll (+9-4) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 6addcfab15125..cbc604e87cf1a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5956,7 +5956,7 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
   }
 
   // Update weight for the newly-created conditional branch.
-  if (hasBranchWeightMD(*SI)) {
+  if (hasBranchWeightMD(*SI) && NewBI->isConditional()) {
     SmallVector<uint64_t, 8> Weights;
     getBranchWeights(SI, Weights);
     if (Weights.size() == 1 + SI->getNumCases()) {
diff --git a/llvm/test/Transforms/SimplifyCFG/pr165301.ll b/llvm/test/Transforms/SimplifyCFG/pr165301.ll
index 4a539d77af3cb..1df655250f57e 100644
--- a/llvm/test/Transforms/SimplifyCFG/pr165301.ll
+++ b/llvm/test/Transforms/SimplifyCFG/pr165301.ll
@@ -1,11 +1,11 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 6
 ; RUN: opt -S -passes="simplifycfg<switch-range-to-icmp>" < %s | FileCheck %s
 
 ; Make sure there's no use after free when removing incoming values from PHI nodes
 
-define i32 @pr165301(i1 %cond) {
+define i32 @pr165301(i1 %cond) !prof !0 {
 ; CHECK-LABEL: define i32 @pr165301(
-; CHECK-SAME: i1 [[COND:%.*]]) {
+; CHECK-SAME: i1 [[COND:%.*]]) !prof [[PROF0:![0-9]+]] {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
 ; CHECK-NEXT:    br label %[[SWITCHBB:.*]]
 ; CHECK:       [[SWITCHBB]]:
@@ -18,9 +18,14 @@ switchbb:
   switch i1 %cond, label %default [
   i1 false, label %switchbb
   i1 true, label %switchbb
-  ]
+  ], !prof !1
 
 default:
   %phi.lcssa = phi i32 [ 0, %switchbb ]
   ret i32 %phi.lcssa
 }
+!0 = !{!"function_entry_count", i32 10}
+!1 = !{!"branch_weights", i32 2, i32 3, i32 5}
+;.
+; CHECK: [[PROF0]] = !{!"function_entry_count", i32 10}
+;.

``````````

</details>


https://github.com/llvm/llvm-project/pull/165931