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[X86] Make sure it is safe to clobber EFLAGS, if need be, when choosing

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the prologue.

Do not use basic blocks that have EFLAGS live-in as prologue if we need
to realign the stack. Realigning the stack uses AND instruction and this
clobbers EFLAGS.

An other alternative would have been to save and restore EFLAGS around
the stack realignment code, but this is likely inefficient.

Fixes PR27531.

llvm-svn: 267634
This commit is contained in:
Quentin Colombet 2016-04-26 23:44:14 +00:00
parent 1caa3a1a82
commit c01de3fc6a
3 changed files with 60 additions and 0 deletions
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6
lib/Target/X86/X86FrameLowering.cpp
View File

@ -2609,6 +2609,12 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
return I;
}
bool X86FrameLowering::canUseAsPrologue(const MachineBasicBlock &MBB) const {
assert(MBB.getParent() && "Block is not attached to a function!");
const MachineFunction &MF = *MBB.getParent();
return !TRI->needsStackRealignment(MF) || !MBB.isLiveIn(X86::EFLAGS);
}
bool X86FrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
assert(MBB.getParent() && "Block is not attached to a function!");

10
lib/Target/X86/X86FrameLowering.h
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@ -127,6 +127,16 @@ public:
/// Check that LEA can be used on SP in an epilogue sequence for \p MF.
bool canUseLEAForSPInEpilogue(const MachineFunction &MF) const;
/// Check whether or not the given \p MBB can be used as a prologue
/// for the target.
/// The prologue will be inserted first in this basic block.
/// This method is used by the shrink-wrapping pass to decide if
/// \p MBB will be correctly handled by the target.
/// As soon as the target enable shrink-wrapping without overriding
/// this method, we assume that each basic block is a valid
/// prologue.
bool canUseAsPrologue(const MachineBasicBlock &MBB) const override;
/// Check whether or not the given \p MBB can be used as a epilogue
/// for the target.
/// The epilogue will be inserted before the first terminator of that block.

44
test/CodeGen/X86/i686-win-shrink-wrapping.ll Normal file
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@ -0,0 +1,44 @@
; RUN: llc %s -o - -enable-shrink-wrap=true | FileCheck %s --check-prefix=CHECK --check-prefix=ENABLE
; RUN: llc %s -o - -enable-shrink-wrap=false | FileCheck %s --check-prefix=CHECK --check-prefix=DISABLE
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"
%struct.S = type { i32 }
; Check that we do not use a basic block that has EFLAGS as live-in
; if we need to realign the stack.
; PR27531.
; CHECK-LABEL: stackRealignment:
; Prologue code.
; CHECK: pushl
; Make sure we actually perform some stack realignment.
; CHECK: andl ${{[-0-9]+}}, %esp
; This is the end of the entry block.
; The prologue should have happened before that point because past
; this point, EFLAGS is live.
; CHECK: jg
define x86_thiscallcc void @stackRealignment(%struct.S* %this) {
entry:
%data = alloca [1 x i32], align 4
%d = alloca double, align 8
%tmp = bitcast [1 x i32]* %data to i8*
%arrayinit.begin = getelementptr inbounds [1 x i32], [1 x i32]* %data, i32 0, i32 0
%x_ = getelementptr inbounds %struct.S, %struct.S* %this, i32 0, i32 0
%tmp1 = load i32, i32* %x_, align 4
%cmp = icmp sgt i32 %tmp1, 32
%cond = select i1 %cmp, i32 42, i32 128
store i32 %cond, i32* %arrayinit.begin, align 4
%cmp3 = icmp slt i32 %tmp1, 32
br i1 %cmp3, label %cleanup, label %if.end
if.end: ; preds = %entry
%tmp2 = bitcast double* %d to i8*
call x86_thiscallcc void @bar(%struct.S* nonnull %this, i32* %arrayinit.begin, double* nonnull %d)
br label %cleanup
cleanup: ; preds = %if.end, %entry
ret void
}
; Function Attrs: optsize
declare x86_thiscallcc void @bar(%struct.S*, i32*, double*)