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[X86] Fix a shrink-wrapping miscompile around __chkstk

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__chkstk clobbers EAX. If EAX is live across the prologue, then we have
to take extra steps to save it. We already had code to do this if EAX
was a register parameter. This change adapts it to work when shrink
wrapping is used.

llvm-svn: 261039
This commit is contained in:
Reid Kleckner 2016-02-17 00:17:33 +00:00
parent fc57478329
commit 30231d4f95
2 changed files with 41 additions and 7 deletions
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13
lib/Target/X86/X86FrameLowering.cpp
View File

@ -192,10 +192,9 @@ static unsigned findDeadCallerSavedReg(MachineBasicBlock &MBB,
return 0;
}
static bool isEAXLiveIn(MachineFunction &MF) {
for (MachineRegisterInfo::livein_iterator II = MF.getRegInfo().livein_begin(),
EE = MF.getRegInfo().livein_end(); II != EE; ++II) {
unsigned Reg = II->first;
static bool isEAXLiveIn(MachineBasicBlock &MBB) {
for (MachineBasicBlock::RegisterMaskPair RegMask : MBB.liveins()) {
unsigned Reg = RegMask.PhysReg;
if (Reg == X86::RAX || Reg == X86::EAX || Reg == X86::AX ||
Reg == X86::AH || Reg == X86::AL)
@ -261,7 +260,7 @@ void X86FrameLowering::emitSPUpdate(MachineBasicBlock &MBB,
// load the offset into a register and do one sub/add
unsigned Reg = 0;
if (isSub && !isEAXLiveIn(*MBB.getParent()))
if (isSub && !isEAXLiveIn(MBB))
Reg = (unsigned)(Is64Bit ? X86::RAX : X86::EAX);
else
Reg = findDeadCallerSavedReg(MBB, MBBI, TRI, Is64Bit);
@ -1138,8 +1137,8 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF,
if (IsWin64Prologue && !IsFunclet && TRI->needsStackRealignment(MF))
AlignedNumBytes = alignTo(AlignedNumBytes, MaxAlign);
if (AlignedNumBytes >= StackProbeSize && UseStackProbe) {
// Check whether EAX is livein for this function.
bool isEAXAlive = isEAXLiveIn(MF);
// Check whether EAX is livein for this block.
bool isEAXAlive = isEAXLiveIn(MBB);
if (isEAXAlive) {
// Sanity check that EAX is not livein for this function.

35
test/CodeGen/X86/shrink-wrap-chkstk.ll
View File

@ -1,6 +1,8 @@
; RUN: llc < %s -enable-shrink-wrap=true | FileCheck %s
; chkstk cannot come before the usual prologue, since it adjusts ESP.
; If chkstk is used in the prologue, we also have to be careful about preserving
; EAX if it is used.
target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
target triple = "i686-pc-windows-msvc18.0.0"
@ -35,3 +37,36 @@ bb2:
; CHECK: retl
declare void @inalloca_params(<{ %struct.S }>* inalloca)
declare i32 @doSomething(i32, i32*)
; In this test case, we force usage of EAX before the prologue, and have to
; compensate before calling __chkstk. It would also be valid for us to avoid
; shrink wrapping in this case.
define x86_fastcallcc i32 @use_eax_before_prologue(i32 inreg %a, i32 inreg %b) {
%tmp = alloca i32, i32 1024, align 4
%tmp2 = icmp slt i32 %a, %b
br i1 %tmp2, label %true, label %false
true:
store i32 %a, i32* %tmp, align 4
%tmp4 = call i32 @doSomething(i32 0, i32* %tmp)
br label %false
false:
%tmp.0 = phi i32 [ %tmp4, %true ], [ %a, %0 ]
ret i32 %tmp.0
}
; CHECK-LABEL: @use_eax_before_prologue@8: # @use_eax_before_prologue
; CHECK: movl %ecx, %eax
; CHECK: cmpl %edx, %eax
; CHECK: jge LBB1_2
; CHECK: pushl %eax
; CHECK: movl $4100, %eax
; CHECK: calll __chkstk
; CHECK: movl 4100(%esp), %eax
; CHECK: calll _doSomething
; CHECK: LBB1_2:
; CHECK: retl