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Produce .weak_def_can_be_hidden for some linkonce_odr values

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With this patch llvm produces a weak_def_can_be_hidden for linkonce_odr
if they are also unnamed_addr or don't have their address taken.

There is not a lot of documentation about .weak_def_can_be_hidden, but
from the old discussion about linkonce_odr_auto_hide and the name of
the directive this looks correct: these symbols can be hidden.

Testing this with the ld64 in Xcode 5 linking clang reduces the number of
exported symbols from 21053 to 19049.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193718 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2013-10-30 22:08:11 +00:00
parent 1d36113c05
commit 2cc546db18
3 changed files with 47 additions and 8 deletions
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2
include/llvm/CodeGen/AsmPrinter.h
View File

@ -486,7 +486,7 @@ namespace llvm {
void EmitVisibility(MCSymbol *Sym, unsigned Visibility,
bool IsDefinition = true) const;
void EmitLinkage(unsigned Linkage, MCSymbol *GVSym) const;
void EmitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const;
void EmitJumpTableEntry(const MachineJumpTableInfo *MJTI,
const MachineBasicBlock *MBB, unsigned uid) const;

27
lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -48,6 +48,7 @@
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
using namespace llvm;
static const char *const DWARFGroupName = "DWARF Emission";
@ -212,9 +213,8 @@ bool AsmPrinter::doInitialization(Module &M) {
llvm_unreachable("Unknown exception type.");
}
void AsmPrinter::EmitLinkage(unsigned L, MCSymbol *GVSym) const {
GlobalValue::LinkageTypes Linkage = (GlobalValue::LinkageTypes)L;
void AsmPrinter::EmitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const {
GlobalValue::LinkageTypes Linkage = GV->getLinkage();
switch (Linkage) {
case GlobalValue::CommonLinkage:
case GlobalValue::LinkOnceAnyLinkage:
@ -227,7 +227,20 @@ void AsmPrinter::EmitLinkage(unsigned L, MCSymbol *GVSym) const {
// .globl _foo
OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
if (Linkage != GlobalValue::LinkOnceODRAutoHideLinkage)
bool CanBeHidden = Linkage == GlobalValue::LinkOnceODRAutoHideLinkage;
if (!CanBeHidden && Linkage == GlobalValue::LinkOnceODRLinkage) {
if (GV->hasUnnamedAddr()) {
CanBeHidden = true;
} else {
GlobalStatus GS;
if (!GlobalStatus::analyzeGlobal(GV, GS) && !GS.IsCompared)
CanBeHidden = true;
}
}
if (!CanBeHidden)
// .weak_definition _foo
OutStreamer.EmitSymbolAttribute(GVSym, MCSA_WeakDefinition);
else
@ -399,7 +412,7 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
OutStreamer.SwitchSection(TLVSect);
// Emit the linkage here.
EmitLinkage(GV->getLinkage(), GVSym);
EmitLinkage(GV, GVSym);
OutStreamer.EmitLabel(GVSym);
// Three pointers in size:
@ -418,7 +431,7 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
OutStreamer.SwitchSection(TheSection);
EmitLinkage(GV->getLinkage(), GVSym);
EmitLinkage(GV, GVSym);
EmitAlignment(AlignLog, GV);
OutStreamer.EmitLabel(GVSym);
@ -444,7 +457,7 @@ void AsmPrinter::EmitFunctionHeader() {
OutStreamer.SwitchSection(getObjFileLowering().SectionForGlobal(F, Mang, TM));
EmitVisibility(CurrentFnSym, F->getVisibility());
EmitLinkage(F->getLinkage(), CurrentFnSym);
EmitLinkage(F, CurrentFnSym);
EmitAlignment(MF->getAlignment(), F);
if (MAI->hasDotTypeDotSizeDirective())

26
test/CodeGen/X86/weak_def_can_be_hidden.ll Normal file
View File

@ -0,0 +1,26 @@
; RUN: llc -mtriple=x86_64-apple-darwin -O0 < %s | FileCheck %s
@v1 = linkonce_odr global i32 32
; CHECK: .globl _v1
; CHECK: .weak_def_can_be_hidden _v1
define i32 @f1() {
%x = load i32 * @v1
ret i32 %x
}
@v2 = linkonce_odr global i32 32
; CHECK: .globl _v2
; CHECK: .weak_definition _v2
@v3 = linkonce_odr unnamed_addr global i32 32
; CHECK: .globl _v3
; CHECK: .weak_def_can_be_hidden _v3
define i32* @f2() {
ret i32* @v2
}
define i32* @f3() {
ret i32* @v3
}