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Avoid unnecessary stack realignment in musttail thunks with SSE2 enabled

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The X86 musttail implementation finds register parameters to forward by
running the calling convention algorithm until a non-register location
is returned. However, assigning a vector memory location has the side
effect of increasing the function's stack alignment. We shouldn't
increase the stack alignment when we are only looking for register
parameters, so this change conditionalizes it.

llvm-svn: 258442
This commit is contained in:
Reid Kleckner 2016-01-21 22:23:22 +00:00
parent 6f240f4b49
commit 4439f8e4ca
3 changed files with 12 additions and 2 deletions
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8
include/llvm/CodeGen/CallingConvLower.h
View File

@ -195,6 +195,7 @@ class CCState {
private:
CallingConv::ID CallingConv;
bool IsVarArg;
bool AnalyzingMustTailForwardedRegs = false;
MachineFunction &MF;
const TargetRegisterInfo &TRI;
SmallVectorImpl<CCValAssign> &Locs;
@ -416,10 +417,15 @@ public:
unsigned Result = StackOffset;
StackOffset += Size;
MaxStackArgAlign = std::max(Align, MaxStackArgAlign);
MF.getFrameInfo()->ensureMaxAlignment(Align);
ensureMaxAlignment(Align);
return Result;
}
void ensureMaxAlignment(unsigned Align) {
if (!AnalyzingMustTailForwardedRegs)
MF.getFrameInfo()->ensureMaxAlignment(Align);
}
/// Version of AllocateStack with extra register to be shadowed.
unsigned AllocateStack(unsigned Size, unsigned Align, unsigned ShadowReg) {
MarkAllocated(ShadowReg);

3
lib/CodeGen/CallingConvLower.cpp
View File

@ -51,7 +51,7 @@ void CCState::HandleByVal(unsigned ValNo, MVT ValVT,
Size = MinSize;
if (MinAlign > (int)Align)
Align = MinAlign;
MF.getFrameInfo()->ensureMaxAlignment(Align);
ensureMaxAlignment(Align);
MF.getSubtarget().getTargetLowering()->HandleByVal(this, Size, Align);
Size = unsigned(alignTo(Size, MinAlign));
unsigned Offset = AllocateStack(Size, Align);
@ -236,6 +236,7 @@ void CCState::analyzeMustTailForwardedRegisters(
// variadic functions, so we need to assume we're not variadic so that we get
// all the registers that might be used in a non-variadic call.
SaveAndRestore<bool> SavedVarArg(IsVarArg, false);
SaveAndRestore<bool> SavedMustTail(AnalyzingMustTailForwardedRegs, true);
for (MVT RegVT : RegParmTypes) {
SmallVector<MCPhysReg, 8> RemainingRegs;

3
test/CodeGen/X86/musttail-varargs.ll
View File

@ -2,6 +2,7 @@
; RUN: llc < %s -enable-tail-merge=0 -mtriple=x86_64-linux-gnux32 | FileCheck %s --check-prefix=LINUX-X32
; RUN: llc < %s -enable-tail-merge=0 -mtriple=x86_64-windows | FileCheck %s --check-prefix=WINDOWS
; RUN: llc < %s -enable-tail-merge=0 -mtriple=i686-windows | FileCheck %s --check-prefix=X86
; RUN: llc < %s -enable-tail-merge=0 -mtriple=i686-windows -mattr=+sse2 | FileCheck %s --check-prefix=X86
; Test that we actually spill and reload all arguments in the variadic argument
; pack. Doing a normal call will clobber all argument registers, and we will
@ -136,6 +137,8 @@ define void @g_thunk(i8* %fptr_i8, ...) {
; WINDOWS: jmpq *%rcx # TAILCALL
; X86-LABEL: _g_thunk:
; X86-NOT: push %ebp
; X86-NOT: andl {{.*}}, %esp
; X86: jmpl *%eax # TAILCALL
; Do a simple multi-exit multi-bb test.