[llvm] [MergeFuncs] Don't introduce calls to weak_odr functions. (PR #125050)
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 30 03:45:44 PST 2025
https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/125050
Avoid creating new calls to weak_odr functions when merging 2 functions.
Consider 2 functions below, both present in 2 modules. Without this
patch, MergeFuncs in the first module may optimize A to call B and in
the second module B to call A.
Note that the 2 optimizations are vaild in isolation, but the linker then
could pick A from module 1 (which calls B) and B from module 2 which
calls A, introducing an infinte call cycle.
There may be other linkage types we need to be more careful about as
well.
define weak_odr hidden void @"A"(ptr %p) {
entry:
tail call void @"foo"(ptr %p)
ret void
}
define weak_odr hidden void @"B"(ptr %p) {
entry:
tail call void @"foo"(ptr %p)
ret void
}
>From 8573e5017b53ced7e42d02d727fbb2ca844c1342 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Thu, 30 Jan 2025 11:32:06 +0000
Subject: [PATCH 1/2] [MergeFunc] Add tests for merging weak_odr functions.
---
.../Transforms/MergeFunc/merge-weak-odr.ll | 100 ++++++++++++++++++
1 file changed, 100 insertions(+)
create mode 100644 llvm/test/Transforms/MergeFunc/merge-weak-odr.ll
diff --git a/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll b/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll
new file mode 100644
index 000000000000000..6afa14c7ec439fa
--- /dev/null
+++ b/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll
@@ -0,0 +1,100 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --include-generated-funcs --version 5
+; RUN: opt -p mergefunc -S %s | FileCheck %s
+
+define weak_odr hidden void @weak_odr_caller_of_foo_1(ptr %p) {
+entry:
+ tail call void @foo(ptr %p)
+ tail call void @foo(ptr %p)
+ tail call void @foo(ptr %p)
+ ret void
+}
+
+define weak_odr hidden void @weak_odr_caller_of_foo_2(ptr %p) {
+entry:
+ tail call void @foo(ptr %p)
+ tail call void @foo(ptr %p)
+ tail call void @foo(ptr %p)
+ ret void
+}
+
+declare void @foo(ptr)
+
+define hidden void @weak_odr_caller_of_bar_1(ptr %p) {
+entry:
+ tail call void @bar(ptr %p)
+ tail call void @bar(ptr %p)
+ tail call void @bar(ptr %p)
+ ret void
+}
+
+define weak_odr hidden void @non_weak_caller_of_bar_2(ptr %p) {
+entry:
+ tail call void @bar(ptr %p)
+ tail call void @bar(ptr %p)
+ tail call void @bar(ptr %p)
+ ret void
+}
+
+declare void @bar(ptr)
+
+define hidden void @non_weak_caller_of_zar_1(ptr %p) {
+entry:
+ tail call void @zar(ptr %p)
+ tail call void @zar(ptr %p)
+ tail call void @zar(ptr %p)
+ ret void
+}
+
+define weak_odr hidden void @weak_odr_caller_of_zar_2(ptr %p) {
+entry:
+ tail call void @zar(ptr %p)
+ tail call void @zar(ptr %p)
+ tail call void @zar(ptr %p)
+ ret void
+}
+
+declare void @zar(ptr)
+; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_foo_1(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: tail call void @foo(ptr [[P]])
+; CHECK-NEXT: tail call void @foo(ptr [[P]])
+; CHECK-NEXT: tail call void @foo(ptr [[P]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define weak_odr hidden void @non_weak_caller_of_bar_2(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: tail call void @bar(ptr [[P]])
+; CHECK-NEXT: tail call void @bar(ptr [[P]])
+; CHECK-NEXT: tail call void @bar(ptr [[P]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define hidden void @non_weak_caller_of_zar_1(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: tail call void @zar(ptr [[P]])
+; CHECK-NEXT: tail call void @zar(ptr [[P]])
+; CHECK-NEXT: tail call void @zar(ptr [[P]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_foo_2(
+; CHECK-SAME: ptr [[TMP0:%.*]]) {
+; CHECK-NEXT: tail call void @weak_odr_caller_of_foo_1(ptr [[TMP0]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define hidden void @weak_odr_caller_of_bar_1(
+; CHECK-SAME: ptr [[TMP0:%.*]]) {
+; CHECK-NEXT: tail call void @non_weak_caller_of_bar_2(ptr [[TMP0]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_zar_2(
+; CHECK-SAME: ptr [[TMP0:%.*]]) {
+; CHECK-NEXT: tail call void @non_weak_caller_of_zar_1(ptr [[TMP0]])
+; CHECK-NEXT: ret void
+;
>From 43ff025297927ab6f91dd69dfeb28f8ec28e2877 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Thu, 30 Jan 2025 11:33:12 +0000
Subject: [PATCH 2/2] [MergeFuncs] Don't introduce calls to weak_odr functions.
Avoid creating new calls to weak_odr functions when merging 2 functions.
Consider 2 functions below, both present in 2 modules. Without this
patch, MergeFuncs in the first module may optimize A to call B and in
the second module B to call A.
Note that the 2 optimizations are vaild in isolation, but the linker then
could pick A from module 1 (which calls B) and B from module 2 which
calls A, introducing an infinte call cycle.
There may be other linkage types we need to be more careful about as
well.
define weak_odr hidden void @"A"(ptr %p) {
entry:
tail call void @"foo"(ptr %p)
ret void
}
define weak_odr hidden void @"B"(ptr %p) {
entry:
tail call void @"foo"(ptr %p)
ret void
}
---
llvm/lib/Transforms/IPO/MergeFunctions.cpp | 4 ++--
.../Transforms/MergeFunc/merge-weak-odr.ll | 20 +++++++++++++++----
2 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index e8508416f542754..d991ec64445ee99 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -891,8 +891,8 @@ bool MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
// Merge two equivalent functions. Upon completion, Function G is deleted.
void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
- if (F->isInterposable()) {
- assert(G->isInterposable());
+ if (F->isInterposable() || G->hasWeakODRLinkage()) {
+ assert(G->isInterposable() || G->hasWeakODRLinkage());
// Both writeThunkOrAlias() calls below must succeed, either because we can
// create aliases for G and NewF, or because a thunk for F is profitable.
diff --git a/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll b/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll
index 6afa14c7ec439fa..d2e89092b9a8266 100644
--- a/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll
+++ b/llvm/test/Transforms/MergeFunc/merge-weak-odr.ll
@@ -54,7 +54,7 @@ entry:
}
declare void @zar(ptr)
-; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_foo_1(
+; CHECK-LABEL: define private void @0(
; CHECK-SAME: ptr [[P:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: tail call void @foo(ptr [[P]])
@@ -72,7 +72,7 @@ declare void @zar(ptr)
; CHECK-NEXT: ret void
;
;
-; CHECK-LABEL: define hidden void @non_weak_caller_of_zar_1(
+; CHECK-LABEL: define private void @1(
; CHECK-SAME: ptr [[P:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: tail call void @zar(ptr [[P]])
@@ -83,7 +83,13 @@ declare void @zar(ptr)
;
; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_foo_2(
; CHECK-SAME: ptr [[TMP0:%.*]]) {
-; CHECK-NEXT: tail call void @weak_odr_caller_of_foo_1(ptr [[TMP0]])
+; CHECK-NEXT: tail call void @[[GLOB0:[0-9]+]](ptr [[TMP0]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_foo_1(
+; CHECK-SAME: ptr [[TMP0:%.*]]) {
+; CHECK-NEXT: tail call void @[[GLOB0]](ptr [[TMP0]])
; CHECK-NEXT: ret void
;
;
@@ -95,6 +101,12 @@ declare void @zar(ptr)
;
; CHECK-LABEL: define weak_odr hidden void @weak_odr_caller_of_zar_2(
; CHECK-SAME: ptr [[TMP0:%.*]]) {
-; CHECK-NEXT: tail call void @non_weak_caller_of_zar_1(ptr [[TMP0]])
+; CHECK-NEXT: tail call void @[[GLOB1:[0-9]+]](ptr [[TMP0]])
+; CHECK-NEXT: ret void
+;
+;
+; CHECK-LABEL: define hidden void @non_weak_caller_of_zar_1(
+; CHECK-SAME: ptr [[TMP0:%.*]]) {
+; CHECK-NEXT: tail call void @[[GLOB1]](ptr [[TMP0]])
; CHECK-NEXT: ret void
;
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