[llvm] 3afc3f4 - [MergeFunc] Remove discardables function before writing alias or thunk. (#128865)
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Thu Feb 27 07:27:09 PST 2025
Author: Florian Hahn
Date: 2025-02-27T15:27:05Z
New Revision: 3afc3f43f0ba155e9655367c8bfa25eff5dfaf0f
URL: https://github.com/llvm/llvm-project/commit/3afc3f43f0ba155e9655367c8bfa25eff5dfaf0f
DIFF: https://github.com/llvm/llvm-project/commit/3afc3f43f0ba155e9655367c8bfa25eff5dfaf0f.diff
LOG: [MergeFunc] Remove discardables function before writing alias or thunk. (#128865)
Update writeThunkOrAlias to only create an alias or thunk if it is
actually needed. Drop discardable linkone_odr functions if they are not
used before.
PR: https://github.com/llvm/llvm-project/pull/128865
Added:
Modified:
llvm/lib/Transforms/IPO/MergeFunctions.cpp
llvm/test/Transforms/MergeFunc/linkonce.ll
llvm/test/Transforms/MergeFunc/linkonce_odr.ll
llvm/test/Transforms/MergeFunc/merge-linkonce-odr.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 9cc159830b17d..d2443a83535e4 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -283,9 +283,10 @@ class MergeFunctions {
// Replace G with an alias to F (deleting function G)
void writeAlias(Function *F, Function *G);
- // Replace G with an alias to F if possible, or a thunk to F if possible.
- // Returns false if neither is the case.
- bool writeThunkOrAlias(Function *F, Function *G);
+ // If needed, replace G with an alias to F if possible, or a thunk to F if
+ // profitable. Returns false if neither is the case. If \p G is not needed
+ // (i.e. it is discardable and not used), \p G is removed directly.
+ bool writeThunkOrAliasIfNeeded(Function *F, Function *G);
/// Replace function F with function G in the function tree.
void replaceFunctionInTree(const FunctionNode &FN, Function *G);
@@ -875,9 +876,14 @@ void MergeFunctions::writeAlias(Function *F, Function *G) {
++NumAliasesWritten;
}
-// Replace G with an alias to F if possible, or a thunk to F if
-// profitable. Returns false if neither is the case.
-bool MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
+// If needed, replace G with an alias to F if possible, or a thunk to F if
+// profitable. Returns false if neither is the case. If \p G is not needed (i.e.
+// it is discardable and unused), \p G is removed directly.
+bool MergeFunctions::writeThunkOrAliasIfNeeded(Function *F, Function *G) {
+ if (G->isDiscardableIfUnused() && G->use_empty() && !MergeFunctionsPDI) {
+ G->eraseFromParent();
+ return true;
+ }
if (canCreateAliasFor(G)) {
writeAlias(F, G);
return true;
@@ -904,9 +910,10 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
assert((!isODR(G) || isODR(F)) &&
"if G is ODR, F must also be ODR due to ordering");
- // Both writeThunkOrAlias() calls below must succeed, either because we can
- // create aliases for G and NewF, or because a thunk for F is profitable.
- // F here has the same signature as NewF below, so that's what we check.
+ // Both writeThunkOrAliasIfNeeded() calls below must succeed, either because
+ // we can create aliases for G and NewF, or because a thunk for F is
+ // profitable. F here has the same signature as NewF below, so that's what
+ // we check.
if (!canCreateThunkFor(F) &&
(!canCreateAliasFor(F) || !canCreateAliasFor(G)))
return;
@@ -930,13 +937,13 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
if (isODR(F))
replaceDirectCallers(NewF, F);
- // We collect alignment before writeThunkOrAlias that overwrites NewF and
- // G's content.
+ // We collect alignment before writeThunkOrAliasIfNeeded that overwrites
+ // NewF and G's content.
const MaybeAlign NewFAlign = NewF->getAlign();
const MaybeAlign GAlign = G->getAlign();
- writeThunkOrAlias(F, G);
- writeThunkOrAlias(F, NewF);
+ writeThunkOrAliasIfNeeded(F, G);
+ writeThunkOrAliasIfNeeded(F, NewF);
if (NewFAlign || GAlign)
F->setAlignment(std::max(NewFAlign.valueOrOne(), GAlign.valueOrOne()));
@@ -975,7 +982,7 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
return;
}
- if (writeThunkOrAlias(F, G)) {
+ if (writeThunkOrAliasIfNeeded(F, G)) {
++NumFunctionsMerged;
}
}
diff --git a/llvm/test/Transforms/MergeFunc/linkonce.ll b/llvm/test/Transforms/MergeFunc/linkonce.ll
index 2f648edc62408..567139d97a387 100644
--- a/llvm/test/Transforms/MergeFunc/linkonce.ll
+++ b/llvm/test/Transforms/MergeFunc/linkonce.ll
@@ -1,5 +1,4 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --include-generated-funcs --version 5
-; RUN: opt -S -passes=mergefunc < %s | FileCheck %s -implicit-check-not=funC
+; RUN: opt -S -passes=mergefunc < %s | FileCheck %s -implicit-check-not=funA -implicit-check-not=funC
; Replacments should be totally ordered on the function name.
; If we don't do this we can end up with one module defining a thunk for @funA
@@ -43,14 +42,8 @@ define linkonce i32 @funA(i32 %x, i32 %y) {
; CHECK-NEXT: ret i32 [[SUM3]]
;
;
-; CHECK-LABEL: define linkonce i32 @funC(
-; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
-; CHECK-NEXT: [[TMP3:%.*]] = tail call i32 @[[GLOB0:[0-9]+]](i32 [[TMP0]], i32 [[TMP1]])
-; CHECK-NEXT: ret i32 [[TMP3]]
-;
-;
; CHECK-LABEL: define linkonce i32 @funB(
; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
-; CHECK-NEXT: [[TMP3:%.*]] = tail call i32 @[[GLOB0]](i32 [[TMP0]], i32 [[TMP1]])
+; CHECK-NEXT: [[TMP3:%.*]] = tail call i32 @0(i32 [[TMP0]], i32 [[TMP1]])
; CHECK-NEXT: ret i32 [[TMP3]]
;
diff --git a/llvm/test/Transforms/MergeFunc/linkonce_odr.ll b/llvm/test/Transforms/MergeFunc/linkonce_odr.ll
index ecbe6f08ab8c2..a1cae60685da1 100644
--- a/llvm/test/Transforms/MergeFunc/linkonce_odr.ll
+++ b/llvm/test/Transforms/MergeFunc/linkonce_odr.ll
@@ -1,5 +1,4 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --include-generated-funcs --version 5
-; RUN: opt -S -passes=mergefunc < %s | FileCheck %s -implicit-check-not=funC
+; RUN: opt -S -passes=mergefunc < %s | FileCheck %s -implicit-check-not=funA -implicit-check-not=funC
; Replacments should be totally ordered on the function name.
; If we don't do this we can end up with one module defining a thunk for @funA
@@ -43,14 +42,8 @@ define linkonce_odr i32 @funA(i32 %x, i32 %y) {
; CHECK-NEXT: ret i32 [[SUM3]]
;
;
-; CHECK-LABEL: define linkonce_odr i32 @funC(
-; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
-; CHECK-NEXT: [[TMP3:%.*]] = tail call i32 @[[GLOB0:[0-9]+]](i32 [[TMP0]], i32 [[TMP1]])
-; CHECK-NEXT: ret i32 [[TMP3]]
-;
-;
; CHECK-LABEL: define linkonce_odr i32 @funB(
; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
-; CHECK-NEXT: [[TMP3:%.*]] = tail call i32 @[[GLOB0]](i32 [[TMP0]], i32 [[TMP1]])
+; CHECK-NEXT: [[TMP3:%.*]] = tail call i32 @0(i32 [[TMP0]], i32 [[TMP1]])
; CHECK-NEXT: ret i32 [[TMP3]]
;
diff --git a/llvm/test/Transforms/MergeFunc/merge-linkonce-odr.ll b/llvm/test/Transforms/MergeFunc/merge-linkonce-odr.ll
index 7e815e1f50d64..1a622bfae72c4 100644
--- a/llvm/test/Transforms/MergeFunc/merge-linkonce-odr.ll
+++ b/llvm/test/Transforms/MergeFunc/merge-linkonce-odr.ll
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --include-generated-funcs --version 5
-; RUN: opt -p mergefunc -S %s | FileCheck %s
+; RUN: opt -p mergefunc -S %s | FileCheck --implicit-check-not=linkonce_odr_caller_of_foo_2 --implicit-check-not=linkonce_odr_caller_of_foo_1 %s
define void @caller_of_callers(ptr %p) {
call void @linkonce_odr_caller_of_foo_1(ptr %p)
@@ -125,15 +125,3 @@ declare void @zar(ptr)
; CHECK-NEXT: tail call void @zar(ptr [[P]])
; CHECK-NEXT: ret void
;
-;
-; CHECK-LABEL: define linkonce_odr hidden void @linkonce_odr_caller_of_foo_2(
-; CHECK-SAME: ptr [[TMP0:%.*]]) {
-; CHECK-NEXT: tail call void @[[GLOB0]](ptr [[TMP0]])
-; CHECK-NEXT: ret void
-;
-;
-; CHECK-LABEL: define linkonce_odr hidden void @linkonce_odr_caller_of_foo_1(
-; CHECK-SAME: ptr [[TMP0:%.*]]) {
-; CHECK-NEXT: tail call void @[[GLOB0]](ptr [[TMP0]])
-; CHECK-NEXT: ret void
-;
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