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ARM: permit tail calls to weak externals on COFF 

Weak externals are resolved statically, so we can actually generate the tail
call on PE/COFF targets without breaking the requirements.  It is questionable
whether we want to propagate the current behaviour for MachO as the requirements
are part of the ARM ELF specifications, and it seems that prior to the SVN
r215890, we would have tail'ed the call.  For now, be conservative and only
permit it on PE/COFF where the call will always be fully resolved.

llvm-svn: 225119
This commit is contained in:
Saleem Abdulrasool 2015-01-03 21:35:00 +00:00
parent 22fe771f78
commit 67f729933f
3 changed files with 25 additions and 2 deletions
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4
llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
View File

@ -2358,7 +2358,9 @@ bool AArch64TargetLowering::isEligibleForTailCallOptimization(
// cannot rely on the linker replacing the tail call with a return.
if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
const GlobalValue *GV = G->getGlobal();
if (GV->hasExternalWeakLinkage())
const Triple TT(getTargetMachine().getTargetTriple());
if (GV->hasExternalWeakLinkage() &&
(!TT.isOSWindows() || TT.isOSBinFormatELF() || TT.isOSBinFormatMachO()))
return false;
}

4
llvm/lib/Target/ARM/ARMISelLowering.cpp
View File

@ -2026,7 +2026,9 @@ ARMTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
// cannot rely on the linker replacing the tail call with a return.
if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
const GlobalValue *GV = G->getGlobal();
if (GV->hasExternalWeakLinkage())
const Triple TT(getTargetMachine().getTargetTriple());
if (GV->hasExternalWeakLinkage() &&
(!TT.isOSWindows() || TT.isOSBinFormatELF() || TT.isOSBinFormatMachO()))
return false;
}

19
llvm/test/CodeGen/ARM/tail-call-weak.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: llc -mtriple thumbv7-windows-coff -filetype asm -o - %s | FileCheck %s -check-prefix CHECK-COFF
; RUN: llc -mtriple thumbv7-elf -filetype asm -o - %s | FileCheck %s -check-prefix CHECK-ELF
; RUN: llc -mtriple thumbv7-macho -filetype asm -o - %s | FileCheck %s -check-prefix CHECK-MACHO
declare i8* @f()
declare extern_weak i8* @g(i8*)
; weak symbol resolution occurs statically in PE/COFF, ensure that we permit
; tail calls on weak externals when targeting a COFF environment.
define void @test() {
%call = tail call i8* @f()
%call1 = tail call i8* @g(i8* %call)
ret void
}
; CHECK-COFF: b g
; CHECK-ELF: bl g
; CHECK-MACHO: blx _g