[llvm] [InstCombine] Abandon BranchProbabilityAnalysis cache result (PR #86470)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Haohai Wen (HaohaiWen)

<details>
<summary>Changes</summary>

InstCombine may invert branch condition and profile metadata. In such
case, BranchProbabilityAnalysis should be rerun.

---
Full diff: https://github.com/llvm/llvm-project/pull/86470.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+1) 
- (added) llvm/test/Transforms/InstCombine/abandon-bpi.ll (+36) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 7c40fb4fc86082..ff7b0b917b712a 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -5314,6 +5314,7 @@ PreservedAnalyses InstCombinePass::run(Function &F,
   // Mark all the analyses that instcombine updates as preserved.
   PreservedAnalyses PA;
   PA.preserveSet<CFGAnalyses>();
+  PA.abandon<BranchProbabilityAnalysis>();
   return PA;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/abandon-bpi.ll b/llvm/test/Transforms/InstCombine/abandon-bpi.ll
new file mode 100644
index 00000000000000..fadb2ab16bff6f
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/abandon-bpi.ll
@@ -0,0 +1,36 @@
+; RUN: opt < %s -passes="print<branch-prob>,instcombine,print<branch-prob>" -S 2>&1 | FileCheck %s
+
+; CHECK:      Printing analysis 'Branch Probability Analysis' for function 'invert_cond':
+; CHECK-NEXT: ---- Branch Probabilities ----
+; CHECK-NEXT:   edge %entry -> %bb1 probability is 0x06186186 / 0x80000000 = 4.76%
+; CHECK-NEXT:   edge %entry -> %bb2 probability is 0x79e79e7a / 0x80000000 = 95.24% [HOT edge]
+; CHECK-NEXT: Printing analysis 'Branch Probability Analysis' for function 'invert_cond':
+; CHECK-NEXT: ---- Branch Probabilities ----
+; CHECK-NEXT:   edge %entry -> %bb2 probability is 0x79e79e7a / 0x80000000 = 95.24% [HOT edge]
+; CHECK-NEXT:   edge %entry -> %bb1 probability is 0x06186186 / 0x80000000 = 4.76%
+
+define i32 @invert_cond(ptr %p) {
+; CHECK-LABEL: define i32 @invert_cond(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[COND_NOT:%.*]] = icmp eq ptr [[P]], null
+; CHECK-NEXT:    br i1 [[COND_NOT]], label [[BB2:%.*]], label [[BB1:%.*]], !prof [[PROF0:![0-9]+]]
+; CHECK:       bb1:
+; CHECK-NEXT:    ret i32 0
+; CHECK:       bb2:
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  %cond = icmp ne ptr %p, null
+  br i1 %cond, label %bb1, label %bb2, !prof !1
+
+bb1:
+  ret i32 0;
+
+bb2:
+  ret i32 1;
+}
+
+!1 = !{!"branch_weights", i32 1, i32 20}
+; CHECK: [[PROF0]] = !{!"branch_weights", i32 20, i32 1}
+

``````````

</details>


https://github.com/llvm/llvm-project/pull/86470