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Fix access to undefined weak symbols in pic code 

When the access to a weak symbol is not a call, the access has to be
able to produce the value 0 at runtime.

We were sometimes producing code sequences where that was not possible
if the code was leaded more than 4g away from 0.

llvm-svn: 310756
This commit is contained in:
Rafael Espindola 2017-08-11 20:49:27 +00:00
parent f6822c869c
commit b8956a70d3
2 changed files with 75 additions and 1 deletions
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18
llvm/lib/Target/X86/X86Subtarget.cpp
View File

@ -99,6 +99,22 @@ X86Subtarget::classifyLocalReference(const GlobalValue *GV) const {
return X86II::MO_GOTOFF;
}
static bool shouldAssumeGlobalReferenceLocal(const X86Subtarget *ST,
const TargetMachine &TM,
const Module &M,
const GlobalValue *GV) {
if (!TM.shouldAssumeDSOLocal(M, GV))
return false;
// A weak reference can end up being 0. If the code can be more that 4g away
// from zero and we are using the small code model we have to treat it as non
// local.
if (GV && GV->hasExternalWeakLinkage() &&
TM.getCodeModel() == CodeModel::Small && TM.isPositionIndependent() &&
ST->is64Bit() && ST->isTargetELF())
return false;
return true;
}
unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
const Module &M) const {
// Large model never uses stubs.
@ -118,7 +134,7 @@ unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
}
}
if (TM.shouldAssumeDSOLocal(M, GV))
if (shouldAssumeGlobalReferenceLocal(this, TM, M, GV))
return classifyLocalReference(GV);
if (isTargetCOFF())

58
llvm/test/CodeGen/X86/weak-undef.ll Normal file
View File

@ -0,0 +1,58 @@
; RUN: llc < %s -relocation-model=pic -mtriple=x86_64-pc-linux | FileCheck %s
; RUN: llc < %s -relocation-model=pic -mtriple=i386-pc-linux | FileCheck --check-prefix=I386 %s
@foo1 = extern_weak hidden global i32, align 4
define i32* @bar1() {
ret i32* @foo1
}
; CHECK: bar1:
; CHECK: movq foo1@GOTPCREL(%rip), %rax
; I386: bar1:
; I386: leal foo1@GOTOFF(%eax), %eax
@foo2 = external hidden global i32, align 4
define i32* @bar2() {
ret i32* @foo2
}
; CHECK: bar2:
; CHECK: leaq foo2(%rip), %rax
; I386: bar2:
; I386: leal foo2@GOTOFF(%eax), %eax
declare extern_weak hidden void @foo3()
define void @bar3() {
call void @foo3()
ret void
}
; CHECK: bar3:
; CHECK: callq foo3
; I386: bar3:
; I386: calll foo3
declare external hidden void @foo4()
define void @bar4() {
call void @foo4()
ret void
}
; CHECK: bar4:
; CHECK: callq foo4
; I386: bar4:
; I386: calll foo4
declare extern_weak hidden i32 @foo5()
define i32()* @bar5() {
ret i32()* @foo5
}
; CHECK: bar5:
; CHECK: movq foo5@GOTPCREL(%rip), %rax
; I386: bar5:
; I386: leal foo5@GOTOFF(%eax), %eax
declare external hidden i32 @foo6()
define i32()* @bar6() {
ret i32()* @foo6
}
; CHECK: bar6:
; CHECK: leaq foo6(%rip), %rax
; I386: bar6:
; I386: leal foo6@GOTOFF(%eax), %eax