[llvm] [profcheck] Add unknown branch weight for inlined memchr calls. (PR #160964)
Mircea Trofin via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 29 16:53:52 PDT 2025
https://github.com/mtrofin updated https://github.com/llvm/llvm-project/pull/160964
>From 3aa7f6fdb13d02510f9c6c136c7deb2653e316bb Mon Sep 17 00:00:00 2001
From: Jin Huang <jingold at google.com>
Date: Fri, 26 Sep 2025 22:55:39 +0000
Subject: [PATCH] [profcheck] Add unknown branch weight for inlined memchr
calls.
---
.../AggressiveInstCombine.cpp | 4 ++
.../AggressiveInstCombine/memchr.ll | 51 ++++++++++++-------
2 files changed, 36 insertions(+), 19 deletions(-)
diff --git a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
index ee1fec0da3d73..805bdb41737c1 100644
--- a/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
+++ b/llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp
@@ -1350,6 +1350,10 @@ static bool foldMemChr(CallInst *Call, DomTreeUpdater *DTU,
BB->getTerminator()->eraseFromParent();
SwitchInst *SI = IRB.CreateSwitch(
IRB.CreateTrunc(Call->getArgOperand(1), ByteTy), BBNext, N);
+ // We can't know the precise weights here, as they would depend on the value
+ // distribution of Call->getArgOperand(1). So we just mark it as "unknown".
+ setExplicitlyUnknownBranchWeightsIfProfiled(*SI, *Call->getFunction(),
+ DEBUG_TYPE);
Type *IndexTy = DL.getIndexType(Call->getType());
SmallVector<DominatorTree::UpdateType, 8> Updates;
diff --git a/llvm/test/Transforms/AggressiveInstCombine/memchr.ll b/llvm/test/Transforms/AggressiveInstCombine/memchr.ll
index b26320be634b8..6fbe960109098 100644
--- a/llvm/test/Transforms/AggressiveInstCombine/memchr.ll
+++ b/llvm/test/Transforms/AggressiveInstCombine/memchr.ll
@@ -6,9 +6,10 @@
declare ptr @memchr(ptr, i32, i64)
-define i1 @test_memchr_null(i32 %x) {
+define i1 @test_memchr_null(i32 %x) !prof !0 {
; CHECK-LABEL: define i1 @test_memchr_null(
-; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]])
+; CHECK: !prof [[PROF_0:![0-9]+]] {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
; CHECK-NEXT: switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
@@ -40,9 +41,10 @@ entry:
ret i1 %isnull
}
-define ptr @test_memchr(i32 %x) {
+define ptr @test_memchr(i32 %x) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr(
-; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
; CHECK-NEXT: switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
@@ -72,16 +74,17 @@ entry:
ret ptr %memchr
}
-define ptr @test_memchr_smaller_n(i32 %x) {
+define ptr @test_memchr_smaller_n(i32 %x) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr_smaller_n(
-; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
; CHECK-NEXT: switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
; CHECK-NEXT: i8 48, label %[[MEMCHR_CASE:.*]]
; CHECK-NEXT: i8 49, label %[[MEMCHR_CASE1:.*]]
; CHECK-NEXT: i8 0, label %[[MEMCHR_CASE2:.*]]
-; CHECK-NEXT: ]
+; CHECK-NEXT: ], !prof [[PROF_1:![0-9]+]]
; CHECK: [[MEMCHR_CASE]]:
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS:.*]]
; CHECK: [[MEMCHR_CASE1]]:
@@ -103,9 +106,10 @@ entry:
; negative tests
-define ptr @test_memchr_larger_n(i32 %x) {
+define ptr @test_memchr_larger_n(i32 %x) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr_larger_n(
-; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr @str, i32 [[X]], i64 6)
; CHECK-NEXT: ret ptr [[MEMCHR]]
@@ -115,9 +119,10 @@ entry:
ret ptr %memchr
}
-define ptr @test_memchr_non_constant(i32 %x, ptr %str) {
+define ptr @test_memchr_non_constant(i32 %x, ptr %str) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr_non_constant(
-; CHECK-SAME: i32 [[X:%.*]], ptr [[STR:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]], ptr [[STR:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr [[STR]], i32 [[X]], i64 5)
; CHECK-NEXT: ret ptr [[MEMCHR]]
@@ -127,8 +132,9 @@ entry:
ret ptr %memchr
}
-define ptr @test_memchr_constant_ch() {
-; CHECK-LABEL: define ptr @test_memchr_constant_ch() {
+define ptr @test_memchr_constant_ch() !prof !0 {
+; CHECK-LABEL: define ptr @test_memchr_constant_ch()
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr @str, i32 49, i64 5)
; CHECK-NEXT: ret ptr [[MEMCHR]]
@@ -138,9 +144,10 @@ entry:
ret ptr %memchr
}
-define ptr @test_memchr_dynamic_n(i32 %x, i32 %y) {
+define ptr @test_memchr_dynamic_n(i32 %x, i32 %y) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr_dynamic_n(
-; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr @str, i32 [[X]], i32 [[Y]])
; CHECK-NEXT: ret ptr [[MEMCHR]]
@@ -150,9 +157,10 @@ entry:
ret ptr %memchr
}
-define ptr @test_memchr_long(i32 %x) {
+define ptr @test_memchr_long(i32 %x) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr_long(
-; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr @str_long, i32 [[X]], i64 8)
; CHECK-NEXT: ret ptr [[MEMCHR]]
@@ -163,9 +171,10 @@ entry:
}
; We want to check that the compiler still calls memchr if the length is non-constant:
-define ptr @test_memchr_non_constant_length2(i32 %x, i64 %len) {
+define ptr @test_memchr_non_constant_length2(i32 %x, i64 %len) !prof !0 {
; CHECK-LABEL: define ptr @test_memchr_non_constant_length2(
-; CHECK-SAME: i32 [[X:%.*]], i64 [[LEN:%.*]]) {
+; CHECK-SAME: i32 [[X:%.*]], i64 [[LEN:%.*]])
+; CHECK: !prof [[PROF_0]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr @str, i32 [[X]], i64 [[LEN]])
; CHECK-NEXT: ret ptr [[MEMCHR]]
@@ -174,3 +183,7 @@ entry:
%memchr = call ptr @memchr(ptr @str, i32 %x, i64 %len)
ret ptr %memchr
}
+
+!0 = !{!"function_entry_count", i64 1000}
+; CHECK: [[PROF_0]] = !{!"function_entry_count", i64 1000}
+; CHECK: [[PROF_1]] = !{!"unknown", !"aggressive-instcombine"}
\ No newline at end of file
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