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

[Haohai Wen via llvm-commits]

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

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

>From e80e7433137f37fe6885faac1802be19acfbf3d3 Mon Sep 17 00:00:00 2001
From: Haohai Wen <haohai.wen at intel.com>
Date: Mon, 25 Mar 2024 15:03:30 +0800
Subject: [PATCH 1/2] [InstCombine] Add test to track BPI when condition was
 inverted

InstCombine may invert branch condition and profile metadata. Branch
probability analysis should not be preserved in this case.
---
 .../Transforms/InstCombine/abandon-bpi.ll     | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 llvm/test/Transforms/InstCombine/abandon-bpi.ll

diff --git a/llvm/test/Transforms/InstCombine/abandon-bpi.ll b/llvm/test/Transforms/InstCombine/abandon-bpi.ll
new file mode 100644
index 00000000000000..190a686c8f078b
--- /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 0x06186186 / 0x80000000 = 4.76%
+; CHECK-NEXT:   edge %entry -> %bb1 probability is 0x79e79e7a / 0x80000000 = 95.24% [HOT edge]
+
+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}
+

>From aa935d02e3a20cf25c6376e4bac2527b27d7ff52 Mon Sep 17 00:00:00 2001
From: Haohai Wen <haohai.wen at intel.com>
Date: Mon, 25 Mar 2024 15:31:15 +0800
Subject: [PATCH 2/2] [InstCombine] Abandon BranchProbabilityAnalysis cache
 result

InstCombine may invert branch condition and profile metadata. In such
case, BranchProbabilityAnalysis should be rerun.
---
 llvm/lib/Transforms/InstCombine/InstructionCombining.cpp | 1 +
 llvm/test/Transforms/InstCombine/abandon-bpi.ll          | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

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
index 190a686c8f078b..fadb2ab16bff6f 100644
--- a/llvm/test/Transforms/InstCombine/abandon-bpi.ll
+++ b/llvm/test/Transforms/InstCombine/abandon-bpi.ll
@@ -6,8 +6,8 @@
 ; 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 0x06186186 / 0x80000000 = 4.76%
-; CHECK-NEXT:   edge %entry -> %bb1 probability is 0x79e79e7a / 0x80000000 = 95.24% [HOT edge]
+; 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(