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MergeFunctions: Don't replace a weak function use by another equivalent weak function

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We don't know whether the weak functions definition is the definitive definition.

rdar://21303727

llvm-svn: 239422
This commit is contained in:
Arnold Schwaighofer 2015-06-09 18:19:17 +00:00
parent 6bca5ce03f
commit 215d830ec3
2 changed files with 53 additions and 25 deletions
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30
lib/Transforms/IPO/MergeFunctions.cpp
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@ -1397,28 +1397,26 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
if (F->mayBeOverridden()) {
assert(G->mayBeOverridden());
// Make them both thunks to the same internal function.
Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
F->getParent());
H->copyAttributesFrom(F);
H->takeName(F);
removeUsers(F);
F->replaceAllUsesWith(H);
unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
if (HasGlobalAliases) {
// Make them both thunks to the same internal function.
Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
F->getParent());
H->copyAttributesFrom(F);
H->takeName(F);
removeUsers(F);
F->replaceAllUsesWith(H);
unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
writeAlias(F, G);
writeAlias(F, H);
F->setAlignment(MaxAlignment);
F->setLinkage(GlobalValue::PrivateLinkage);
} else {
// We can't merge them. Instead, pick one and update all direct callers
// to call it and hope that we improve the instruction cache hit rate.
replaceDirectCallers(G, F);
writeThunk(F, G);
writeThunk(F, H);
}
F->setAlignment(MaxAlignment);
F->setLinkage(GlobalValue::PrivateLinkage);
++NumDoubleWeak;
} else {
writeThunkOrAlias(F, G);

48
test/Transforms/MergeFunc/fold-weak.ll
View File

@ -1,17 +1,47 @@
; RUN: opt < %s -mergefunc -S > %t
; RUN: grep "define weak" %t | count 2
; RUN: grep "call" %t | count 2
; XFAIL: *
; This test is off for a bit as we change this particular sort of folding to
; only apply on ELF systems and not Mach-O systems.
; RUN: opt -S -mergefunc < %s | FileCheck %s
define weak i32 @sum(i32 %x, i32 %y) {
%sum = add i32 %x, %y
ret i32 %sum
%sum2 = add i32 %sum, %y
%sum3 = add i32 %sum2, %y
ret i32 %sum3
}
define weak i32 @add(i32 %x, i32 %y) {
%sum = add i32 %x, %y
ret i32 %sum
%sum2 = add i32 %sum, %y
%sum3 = add i32 %sum2, %y
ret i32 %sum3
}
; Don't replace a weak function use by another equivalent function. We don't
; know whether the symbol that will ulitmately be linked is equivalent - we
; don't know that the weak definition is the definitive definition or whether it
; will be overriden by a stronger definition).
; CHECK-LABEL: define private i32 @0
; CHECK: add i32
; CHECK: add i32
; CHECK: add i32
; CHECK: ret
; CHECK-LABEL: define i32 @use_weak
; CHECK: call i32 @add
; CHECK: call i32 @sum
; CHECK: ret
; CHECK-LABEL: define weak i32 @sum
; CHECK: tail call i32 @0
; CHECK: ret
; CHECK-LABEL: define weak i32 @add
; CHECK: tail call i32 @0
; CHECK: ret
define i32 @use_weak(i32 %a, i32 %b) {
%res = call i32 @add(i32 %a, i32 %b)
%res2 = call i32 @sum(i32 %a, i32 %b)
%res3 = add i32 %res, %res2
ret i32 %res3
}