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X86, Win64: Allow 'mov' to restore the stack pointer if we have a FP

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The Win64 epilogue structure is very restrictive, it permits a very
small number of opcodes and none of them are 'mov'.

This means that given:
  mov %rbp, %rsp
  pop %rbp

The mov isn't the epilogue, only the pop is.  This is problematic unless
a frame pointer is present in which case we are free to do whatever we'd
like in the "body" of the function.  If a frame pointer is present,
unwinding will undo the prologue operations in reverse order regardless
of the fact that we are at an instruction which is reseting the stack
pointer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230543 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2015-02-25 21:13:37 +00:00
parent dd51ad933e
commit 92d1637e2f
2 changed files with 13 additions and 14 deletions
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25
lib/Target/X86/X86FrameLowering.cpp
View File

@ -1074,21 +1074,20 @@ void X86FrameLowering::emitEpilogue(MachineFunction &MF,
if (RegInfo->needsStackRealignment(MF) || MFI->hasVarSizedObjects()) {
if (RegInfo->needsStackRealignment(MF))
MBBI = FirstCSPop;
if (IsWinEH) {
// There are only two legal forms of epilogue:
// - add SEHAllocationSize, %rsp
// - lea SEHAllocationSize(%FramePtr), %rsp
//
// We are *not* permitted to use 'mov %FramePtr, %rsp' because the Win64
// unwinder will not recognize 'mov' as an epilogue instruction.
unsigned SEHFrameOffset = calculateSetFPREG(SEHStackAllocAmt);
addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(X86::LEA64r), StackPtr),
FramePtr, false, SEHStackAllocAmt - SEHFrameOffset);
--MBBI;
} else if (CSSize != 0) {
unsigned SEHFrameOffset = calculateSetFPREG(SEHStackAllocAmt);
uint64_t LEAAmount = IsWinEH ? SEHStackAllocAmt - SEHFrameOffset : -CSSize;
// There are only two legal forms of epilogue:
// - add SEHAllocationSize, %rsp
// - lea SEHAllocationSize(%FramePtr), %rsp
//
// 'mov %FramePtr, %rsp' will not be recognized as an epilogue sequence.
// However, we may use this sequence if we have a frame pointer because the
// effects of the prologue can safely be undone.
if (LEAAmount != 0) {
unsigned Opc = getLEArOpcode(Uses64BitFramePtr);
addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(Opc), StackPtr),
FramePtr, false, -CSSize);
FramePtr, false, LEAAmount);
--MBBI;
} else {
unsigned Opc = (Uses64BitFramePtr ? X86::MOV64rr : X86::MOV32rr);

2
test/CodeGen/X86/win64_eh.ll
View File

@ -167,7 +167,7 @@ entry:
; WIN64: andq $-64, %rsp
; WIN64: movaps -32(%rbp), %xmm6 # 16-byte Reload
; WIN64: movaps -16(%rbp), %xmm7 # 16-byte Reload
; WIN64: leaq (%rbp), %rsp
; WIN64: movq %rbp, %rsp
; WIN64: popq %rbx
; WIN64: popq %rdi
; WIN64: popq %rbp