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[MergeFunc] Allow merging identical vararg functions using aliases

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Thanks to Nikita Popov for pointing out this missed case.

This is a follow-up to r351411, which disabled function merging for
vararg functions outright due to a miscompile (see llvm.org/PR40345).

Differential Revision: https://reviews.llvm.org/D56865

llvm-svn: 351624
This commit is contained in:
Vedant Kumar 2019-01-19 02:46:22 +00:00
parent 98b18d2ada
commit dac1c75c50
2 changed files with 20 additions and 13 deletions
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25
lib/Transforms/IPO/MergeFunctions.cpp
View File

@ -281,8 +281,8 @@ private:
// 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
// profitable. Returns false if neither is the case.
// 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);
/// Replace function F with function G in the function tree.
@ -385,8 +385,7 @@ bool MergeFunctions::doSanityCheck(std::vector<WeakTrackingVH> &Worklist) {
/// Check whether \p F is eligible for function merging.
static bool isEligibleForMerging(Function &F) {
return !F.isDeclaration() && !F.hasAvailableExternallyLinkage() &&
!F.isVarArg();
return !F.isDeclaration() && !F.hasAvailableExternallyLinkage();
}
bool MergeFunctions::runOnModule(Module &M) {
@ -660,12 +659,16 @@ void MergeFunctions::filterInstsUnrelatedToPDI(
LLVM_DEBUG(dbgs() << " }\n");
}
// Don't merge tiny functions using a thunk, since it can just end up
// making the function larger.
static bool isThunkProfitable(Function * F) {
/// Whether this function may be replaced by a forwarding thunk.
static bool canCreateThunkFor(Function *F) {
if (F->isVarArg())
return false;
// Don't merge tiny functions using a thunk, since it can just end up
// making the function larger.
if (F->size() == 1) {
if (F->front().size() <= 2) {
LLVM_DEBUG(dbgs() << "isThunkProfitable: " << F->getName()
LLVM_DEBUG(dbgs() << "canCreateThunkFor: " << F->getName()
<< " is too small to bother creating a thunk for\n");
return false;
}
@ -793,7 +796,7 @@ bool MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
writeAlias(F, G);
return true;
}
if (isThunkProfitable(F)) {
if (canCreateThunkFor(F)) {
writeThunk(F, G);
return true;
}
@ -808,9 +811,9 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
// 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.
if (!isThunkProfitable(F) && (!canCreateAliasFor(F) || !canCreateAliasFor(G))) {
if (!canCreateThunkFor(F) &&
(!canCreateAliasFor(F) || !canCreateAliasFor(G)))
return;
}
// Make them both thunks to the same internal function.
Function *NewF = Function::Create(F->getFunctionType(), F->getLinkage(),

8
test/Transforms/MergeFunc/va_arg.ll
View File

@ -1,14 +1,18 @@
; RUN: opt -S -mergefunc < %s | FileCheck %s
; RUN: opt -S -mergefunc -mergefunc-use-aliases < %s | FileCheck %s -check-prefix=ALIAS
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
; ALIAS: @_Z9simple_vaPKcz = unnamed_addr alias void (i8*, ...), void (i8*, ...)* @_Z10simple_va2PKcz
; ALIAS-NOT: @_Z9simple_vaPKcz
%struct.__va_list_tag = type { i32, i32, i8*, i8* }
; CHECK-LABEL: define {{.*}}@_Z9simple_vaPKcz
; CHECK: call void @llvm.va_start
; CHECK: call void @llvm.va_end
define dso_local void @_Z9simple_vaPKcz(i8* nocapture readnone, ...) local_unnamed_addr {
define dso_local void @_Z9simple_vaPKcz(i8* nocapture readnone, ...) unnamed_addr {
%2 = alloca [1 x %struct.__va_list_tag], align 16
%3 = bitcast [1 x %struct.__va_list_tag]* %2 to i8*
call void @llvm.va_start(i8* nonnull %3)
@ -54,7 +58,7 @@ declare void @llvm.va_end(i8*)
; CHECK-LABEL: define {{.*}}@_Z10simple_va2PKcz
; CHECK: call void @llvm.va_start
; CHECK: call void @llvm.va_end
define dso_local void @_Z10simple_va2PKcz(i8* nocapture readnone, ...) local_unnamed_addr {
define dso_local void @_Z10simple_va2PKcz(i8* nocapture readnone, ...) unnamed_addr {
%2 = alloca [1 x %struct.__va_list_tag], align 16
%3 = bitcast [1 x %struct.__va_list_tag]* %2 to i8*
call void @llvm.va_start(i8* nonnull %3)