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[X86] Make sure the prologue does not clobber EFLAGS when it lives accross it.
This is a superset of the fix done in r254448. This fixes PR25607. llvm-svn: 254478
This commit is contained in:
Quentin Colombet
parent
c434b24d59
commit
096b1e51ee
@ -204,10 +204,13 @@ static bool isEAXLiveIn(MachineFunction &MF) {
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return false;
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}
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/// Check whether or not the terminators of \p MBB needs to read EFLAGS.
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static bool terminatorsNeedFlagsAsInput(const MachineBasicBlock &MBB) {
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/// Check if the flags need to be preserved before the terminators.
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/// This would be the case, if the eflags is live-in of the region
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/// composed by the terminators or live-out of that region, without
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/// being defined by a terminator.
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static bool
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flagsNeedToBePreservedBeforeTheTerminators(const MachineBasicBlock &MBB) {
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for (const MachineInstr &MI : MBB.terminators()) {
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bool BreakNext = false;
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for (const MachineOperand &MO : MI.operands()) {
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if (!MO.isReg())
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continue;
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@ -215,15 +218,22 @@ static bool terminatorsNeedFlagsAsInput(const MachineBasicBlock &MBB) {
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if (Reg != X86::EFLAGS)
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continue;
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// This terminator needs an eflag that is not defined
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// by a previous terminator.
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// This terminator needs an eflags that is not defined
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// by a previous another terminator:
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// EFLAGS is live-in of the region composed by the terminators.
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if (!MO.isDef())
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return true;
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BreakNext = true;
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// This terminator defines the eflags, i.e., we don't need to preserve it.
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return false;
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}
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if (BreakNext)
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break;
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}
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// None of the terminators use or define the eflags.
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// Check if they are live-out, that would imply we need to preserve them.
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for (const MachineBasicBlock *Succ : MBB.successors())
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if (Succ->isLiveIn(X86::EFLAGS))
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return true;
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return false;
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}
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@ -297,28 +307,6 @@ void X86FrameLowering::emitSPUpdate(MachineBasicBlock &MBB,
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}
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}
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// Check if \p MBB defines the flags register before the first terminator.
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static bool flagsDefinedLocally(const MachineBasicBlock &MBB) {
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MachineBasicBlock::const_iterator FirstTerminator = MBB.getFirstTerminator();
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for (MachineBasicBlock::const_iterator MII : MBB) {
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if (MII == FirstTerminator)
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return false;
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for (const MachineOperand &MO : MII->operands()) {
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (Reg != X86::EFLAGS)
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continue;
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// This instruction sets the eflag.
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if (MO.isDef())
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return true;
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}
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}
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return false;
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}
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MachineInstrBuilder X86FrameLowering::BuildStackAdjustment(
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MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI, DebugLoc DL,
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int64_t Offset, bool InEpilogue) const {
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@ -330,14 +318,9 @@ MachineInstrBuilder X86FrameLowering::BuildStackAdjustment(
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if (!InEpilogue) {
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// Check if inserting the prologue at the beginning
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// of MBB would require to use LEA operations.
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// We need to use LEA operations if both conditions are true:
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// 1. One of the terminators need the flags.
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// 2. The flags are not defined after the insertion point of the prologue.
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// Note: Checking for the predecessors is a shortcut when obviously nothing
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// will live accross the prologue.
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UseLEA = STI.useLeaForSP() ||
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(!MBB.pred_empty() && terminatorsNeedFlagsAsInput(MBB) &&
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!flagsDefinedLocally(MBB));
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// We need to use LEA operations if EFLAGS is live in, because
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// it means an instruction will read it before it gets defined.
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UseLEA = STI.useLeaForSP() || MBB.isLiveIn(X86::EFLAGS);
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} else {
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// If we can use LEA for SP but we shouldn't, check that none
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// of the terminators uses the eflags. Otherwise we will insert
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@ -346,10 +329,10 @@ MachineInstrBuilder X86FrameLowering::BuildStackAdjustment(
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// and is an optimization anyway.
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UseLEA = canUseLEAForSPInEpilogue(*MBB.getParent());
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if (UseLEA && !STI.useLeaForSP())
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UseLEA = terminatorsNeedFlagsAsInput(MBB);
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UseLEA = flagsNeedToBePreservedBeforeTheTerminators(MBB);
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// If that assert breaks, that means we do not do the right thing
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// in canUseAsEpilogue.
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assert((UseLEA || !terminatorsNeedFlagsAsInput(MBB)) &&
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assert((UseLEA || !flagsNeedToBePreservedBeforeTheTerminators(MBB)) &&
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"We shouldn't have allowed this insertion point");
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}
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@ -2597,10 +2580,10 @@ bool X86FrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
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return true;
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// If we cannot use LEA to adjust SP, we may need to use ADD, which
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// clobbers the EFLAGS. Check that none of the terminators reads the
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// EFLAGS, and if one uses it, conservatively assume this is not
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// clobbers the EFLAGS. Check that we do not need to preserve it,
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// otherwise, conservatively assume this is not
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// safe to insert the epilogue here.
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return !terminatorsNeedFlagsAsInput(MBB);
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return !flagsNeedToBePreservedBeforeTheTerminators(MBB);
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}
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MachineBasicBlock::iterator X86FrameLowering::restoreWin32EHStackPointers(
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113
test/CodeGen/X86/i386-shrink-wrapping.ll
Normal file
113
test/CodeGen/X86/i386-shrink-wrapping.ll
Normal file
@ -0,0 +1,113 @@
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; RUN: llc %s -o - -enable-shrink-wrap=true | FileCheck %s --check-prefix=CHECK --check-prefix=ENABLE
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; RUN: llc %s -o - -enable-shrink-wrap=false | FileCheck %s --check-prefix=CHECK --check-prefix=DISABLE
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target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
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target triple = "i386-apple-macosx"
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@a = common global i32 0, align 4
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@d = internal unnamed_addr global i1 false
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@b = common global i32 0, align 4
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@e = common global i8 0, align 1
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@f = common global i8 0, align 1
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@c = common global i32 0, align 4
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@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
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; Check that we are clobbering the flags when they are live-in of the
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; prologue block and the prologue needs to adjust the stack.
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; PR25607.
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;
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; CHECK-LABEL: eflagsLiveInPrologue:
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;
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; DISABLE: pushl
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; DISABLE-NEXT: pushl
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; DISABLE-NEXT: subl $20, %esp
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;
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; CHECK: movl L_a$non_lazy_ptr, [[A:%[a-z]+]]
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; CHECK-NEXT: cmpl $0, ([[A]])
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; CHECK-NEXT: je [[PREHEADER_LABEL:LBB[0-9_]+]]
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;
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; CHECK: movb $1, _d
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;
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; CHECK: [[PREHEADER_LABEL]]:
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; CHECK-NEXT: movl L_b$non_lazy_ptr, [[B:%[a-z]+]]
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; CHECK-NEXT: movl ([[B]]), [[TMP1:%[a-z]+]]
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; CHECK-NEXT: testl [[TMP1]], [[TMP1]]
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; CHECK-NEXT: je [[FOREND_LABEL:LBB[0-9_]+]]
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;
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; Skip the loop.
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; [...]
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;
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; The for.end block is split to accomadate the different selects.
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; We are interested in the one with the call, so skip until the branch.
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; CHECK: [[FOREND_LABEL]]:
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; CHECK-NEXT: movb _d, [[D:%[a-z]+]]
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; [...]
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; CHECK: jne [[CALL_LABEL:LBB[0-9_]+]]
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;
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; CHECK: movb $6, [[D]]
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;
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; CHECK: [[CALL_LABEL]]
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;
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; ENABLE-NEXT: pushl
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; ENABLE-NEXT: pushl
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; We must not use sub here otherwise we will clobber the eflags.
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; ENABLE-NEXT: leal -20(%esp), %esp
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;
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; CHECK-NEXT: L_e$non_lazy_ptr, [[E:%[a-z]+]]
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; CHECK-NEXT: movb [[D]], ([[E]])
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; CHECK-NEXT: L_f$non_lazy_ptr, [[F:%[a-z]+]]
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; CHECK-NEXT: movsbl ([[F]]), [[CONV:%[a-z]+]]
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; CHECK-NEXT: movl $6, [[CONV:%[a-z]+]]
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; The eflags is used in the next instruction.
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; If that instruction disappear, we are not exercising the bug
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; anymore.
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; CHECK-NEXT: cmovnel {{%[a-z]+}}, [[CONV]]
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;
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; Skip all the crust of vaarg lowering.
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; CHECK: calll L_varfunc$stub
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; Set the return value to 0.
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; CHECK-NEXT: xorl %eax, %eax
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; CHECK-NEXT: addl $20, %esp
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; CHECK-NEXT: popl
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; CHECK-NEXT: popl
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; CHECK-NEXT: retl
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define i32 @eflagsLiveInPrologue() #0 {
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entry:
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%tmp = load i32, i32* @a, align 4
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%tobool = icmp eq i32 %tmp, 0
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br i1 %tobool, label %for.cond.preheader, label %if.then
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if.then: ; preds = %entry
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store i1 true, i1* @d, align 1
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br label %for.cond.preheader
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for.cond.preheader: ; preds = %if.then, %entry
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%tmp1 = load i32, i32* @b, align 4
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%tobool14 = icmp eq i32 %tmp1, 0
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br i1 %tobool14, label %for.end, label %for.body.preheader
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for.body.preheader: ; preds = %for.cond.preheader
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br label %for.body
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for.body: ; preds = %for.body, %for.body.preheader
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br label %for.body
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for.end: ; preds = %for.cond.preheader
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%.b3 = load i1, i1* @d, align 1
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%tmp2 = select i1 %.b3, i8 0, i8 6
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store i8 %tmp2, i8* @e, align 1
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%tmp3 = load i8, i8* @f, align 1
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%conv = sext i8 %tmp3 to i32
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%add = add nsw i32 %conv, 1
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%rem = srem i32 %tmp1, %add
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store i32 %rem, i32* @c, align 4
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%conv2 = select i1 %.b3, i32 0, i32 6
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%call = tail call i32 (i8*, ...) @varfunc(i8* nonnull getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i32 0, i32 0), i32 %conv2) #1
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ret i32 0
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}
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; Function Attrs: nounwind
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declare i32 @varfunc(i8* nocapture readonly, ...) #0
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attributes #0 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-features"="+mmx,+sse" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #1 = { nounwind }
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