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Do not consider a machine instruction that uses and defines the same

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physical register as candidate for common subexpression elimination
in MachineCSE.

This fixes a bug on PowerPC in MultiSource/Applications/oggenc/oggenc
caused by MachineCSE invalidly merging two separate DYNALLOC insns.

llvm-svn: 167855
This commit is contained in:
Ulrich Weigand 2012-11-13 18:40:58 +00:00
parent f934185b04
commit 9c5e333c90
2 changed files with 62 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
lib/CodeGen/MachineCSE.cpp
View File

@ -84,7 +84,8 @@ namespace {
bool hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
SmallSet<unsigned,8> &PhysRefs,
SmallVector<unsigned,2> &PhysDefs) const;
SmallVector<unsigned,2> &PhysDefs,
bool &PhysUseDef) const;
bool PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
SmallSet<unsigned,8> &PhysRefs,
SmallVector<unsigned,2> &PhysDefs,
@ -194,31 +195,52 @@ MachineCSE::isPhysDefTriviallyDead(unsigned Reg,
bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
SmallSet<unsigned,8> &PhysRefs,
SmallVector<unsigned,2> &PhysDefs) const{
MachineBasicBlock::const_iterator I = MI; I = llvm::next(I);
SmallVector<unsigned,2> &PhysDefs,
bool &PhysUseDef) const{
// First, add all uses to PhysRefs.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
if (!MO.isReg() || MO.isDef())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (TargetRegisterInfo::isVirtualRegister(Reg))
continue;
// If the def is dead, it's ok. But the def may not marked "dead". That's
// common since this pass is run before livevariables. We can scan
// forward a few instructions and check if it is obviously dead.
if (MO.isDef() &&
(MO.isDead() || isPhysDefTriviallyDead(Reg, I, MBB->end())))
continue;
// Reading constant physregs is ok.
if (!MRI->isConstantPhysReg(Reg, *MBB->getParent()))
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
PhysRefs.insert(*AI);
if (MO.isDef())
}
// Next, collect all defs into PhysDefs. If any is already in PhysRefs
// (which currently contains only uses), set the PhysUseDef flag.
PhysUseDef = false;
MachineBasicBlock::const_iterator I = MI; I = llvm::next(I);
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (TargetRegisterInfo::isVirtualRegister(Reg))
continue;
// Check against PhysRefs even if the def is "dead".
if (PhysRefs.count(Reg))
PhysUseDef = true;
// If the def is dead, it's ok. But the def may not marked "dead". That's
// common since this pass is run before livevariables. We can scan
// forward a few instructions and check if it is obviously dead.
if (!MO.isDead() && !isPhysDefTriviallyDead(Reg, I, MBB->end()))
PhysDefs.push_back(Reg);
}
// Finally, add all defs to PhysRefs as well.
for (unsigned i = 0, e = PhysDefs.size(); i != e; ++i)
for (MCRegAliasIterator AI(PhysDefs[i], TRI, true); AI.isValid(); ++AI)
PhysRefs.insert(*AI);
return !PhysRefs.empty();
}
@ -459,16 +481,22 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
bool CrossMBBPhysDef = false;
SmallSet<unsigned, 8> PhysRefs;
SmallVector<unsigned, 2> PhysDefs;
if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs, PhysDefs)) {
bool PhysUseDef = false;
if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs,
PhysDefs, PhysUseDef)) {
FoundCSE = false;
// ... Unless the CS is local or is in the sole predecessor block
// and it also defines the physical register which is not clobbered
// in between and the physical register uses were not clobbered.
unsigned CSVN = VNT.lookup(MI);
MachineInstr *CSMI = Exps[CSVN];
if (PhysRegDefsReach(CSMI, MI, PhysRefs, PhysDefs, CrossMBBPhysDef))
FoundCSE = true;
// This can never be the case if the instruction both uses and
// defines the same physical register, which was detected above.
if (!PhysUseDef) {
unsigned CSVN = VNT.lookup(MI);
MachineInstr *CSMI = Exps[CSVN];
if (PhysRegDefsReach(CSMI, MI, PhysRefs, PhysDefs, CrossMBBPhysDef))
FoundCSE = true;
}
}
if (!FoundCSE) {

18
test/CodeGen/PowerPC/2012-10-11-dynalloc.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llc < %s | FileCheck %s
target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v128:128:128-n32:64"
target triple = "powerpc64-unknown-linux-gnu"
define void @test(i64 %n) nounwind {
entry:
%0 = alloca i8, i64 %n, align 1
%1 = alloca i8, i64 %n, align 1
call void @use(i8* %0, i8* %1) nounwind
ret void
}
declare void @use(i8*, i8*)
; Check we actually have two instances of dynamic stack allocation,
; identified by the stdux used to update the back-chain link.
; CHECK: stdux
; CHECK: stdux