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Teach machine cse to eliminate instructions with multiple physreg uses and defs. rdar://8610857. 

llvm-svn: 117745
This commit is contained in:
Evan Cheng 2010-10-29 23:36:03 +00:00
parent e89c04e518
commit 2b3f25e031
2 changed files with 52 additions and 51 deletions
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95
llvm/lib/CodeGen/MachineCSE.cpp
View File

@ -22,6 +22,7 @@
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
@ -30,7 +31,8 @@ using namespace llvm;
STATISTIC(NumCoalesces, "Number of copies coalesced");
STATISTIC(NumCSEs, "Number of common subexpression eliminated");
STATISTIC(NumPhysCSEs, "Number of phyreg defining common subexpr eliminated");
STATISTIC(NumPhysCSEs,
"Number of physreg referencing common subexpr eliminated");
namespace {
class MachineCSE : public MachineFunctionPass {
@ -74,11 +76,11 @@ namespace {
bool isPhysDefTriviallyDead(unsigned Reg,
MachineBasicBlock::const_iterator I,
MachineBasicBlock::const_iterator E) const ;
bool hasLivePhysRegDefUse(const MachineInstr *MI,
const MachineBasicBlock *MBB,
unsigned &PhysDef) const;
bool PhysRegDefReaches(MachineInstr *CSMI, MachineInstr *MI,
unsigned PhysDef) const;
bool hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
SmallSet<unsigned,8> &PhysRefs) const;
bool PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
SmallSet<unsigned,8> &PhysRefs) const;
bool isCSECandidate(MachineInstr *MI);
bool isProfitableToCSE(unsigned CSReg, unsigned Reg,
MachineInstr *CSMI, MachineInstr *MI);
@ -177,14 +179,14 @@ MachineCSE::isPhysDefTriviallyDead(unsigned Reg,
return false;
}
/// hasLivePhysRegDefUse - Return true if the specified instruction read / write
/// hasLivePhysRegDefUses - Return true if the specified instruction read/write
/// physical registers (except for dead defs of physical registers). It also
/// returns the physical register def by reference if it's the only one and the
/// instruction does not uses a physical register.
bool MachineCSE::hasLivePhysRegDefUse(const MachineInstr *MI,
const MachineBasicBlock *MBB,
unsigned &PhysDef) const {
PhysDef = 0;
bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
SmallSet<unsigned,8> &PhysRefs) const {
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())
@ -194,35 +196,22 @@ bool MachineCSE::hasLivePhysRegDefUse(const MachineInstr *MI,
continue;
if (TargetRegisterInfo::isVirtualRegister(Reg))
continue;
if (MO.isUse()) {
// Can't touch anything to read a physical register.
PhysDef = 0;
return true;
}
if (MO.isDead())
// If the def is dead, it's ok.
continue;
// Ok, this is a physical register def that's not marked "dead". That's
// 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 (PhysDef) {
// Multiple physical register defs. These are rare, forget about it.
PhysDef = 0;
return true;
}
PhysDef = Reg;
if (MO.isDef() &&
(MO.isDead() || isPhysDefTriviallyDead(Reg, I, MBB->end())))
continue;
PhysRefs.insert(Reg);
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias)
PhysRefs.insert(*Alias);
}
if (PhysDef) {
MachineBasicBlock::const_iterator I = MI; I = llvm::next(I);
if (!isPhysDefTriviallyDead(PhysDef, I, MBB->end()))
return true;
}
return false;
return !PhysRefs.empty();
}
bool MachineCSE::PhysRegDefReaches(MachineInstr *CSMI, MachineInstr *MI,
unsigned PhysDef) const {
bool MachineCSE::PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
SmallSet<unsigned,8> &PhysRefs) const {
// For now conservatively returns false if the common subexpression is
// not in the same basic block as the given instruction.
MachineBasicBlock *MBB = MI->getParent();
@ -238,8 +227,17 @@ bool MachineCSE::PhysRegDefReaches(MachineInstr *CSMI, MachineInstr *MI,
if (I == E)
return true;
if (I->modifiesRegister(PhysDef, TRI))
return false;
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = I->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned MOReg = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(MOReg))
continue;
if (PhysRefs.count(MOReg))
return false;
}
--LookAheadLeft;
++I;
@ -360,7 +358,6 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
if (!isCSECandidate(MI))
continue;
bool DefPhys = false;
bool FoundCSE = VNT.count(MI);
if (!FoundCSE) {
// Look for trivial copy coalescing opportunities.
@ -373,22 +370,20 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
}
// FIXME: commute commutable instructions?
// If the instruction defines a physical register and the value *may* be
// If the instruction defines physical registers and the values *may* be
// used, then it's not safe to replace it with a common subexpression.
unsigned PhysDef = 0;
if (FoundCSE && hasLivePhysRegDefUse(MI, MBB, PhysDef)) {
// It's also not safe if the instruction uses physical registers.
SmallSet<unsigned,8> PhysRefs;
if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs)) {
FoundCSE = false;
// ... Unless the CS is local and it also defines the physical register
// which is not clobbered in between.
if (PhysDef) {
unsigned CSVN = VNT.lookup(MI);
MachineInstr *CSMI = Exps[CSVN];
if (PhysRegDefReaches(CSMI, MI, PhysDef)) {
FoundCSE = true;
DefPhys = true;
}
}
// 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))
FoundCSE = true;
}
if (!FoundCSE) {
@ -433,7 +428,7 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
}
MI->eraseFromParent();
++NumCSEs;
if (DefPhys)
if (!PhysRefs.empty())
++NumPhysCSEs;
} else {
DEBUG(dbgs() << "*** Not profitable, avoid CSE!\n");

8
llvm/test/CodeGen/ARM/fpcmp_ueq.ll
View File

@ -1,8 +1,14 @@
; RUN: llc < %s -march=arm | grep moveq
; RUN: llc < %s -march=arm -mattr=+vfp2 | grep movvs
; RUN: llc < %s -mtriple=armv7-apple-darwin -mcpu=cortex-a8 | FileCheck %s
define i32 @f7(float %a, float %b) {
entry:
; CHECK: f7:
; CHECK: vcmpe.f32
; CHECK: vmrs apsr_nzcv, fpscr
; CHECK: movweq
; CHECK-NOT: vmrs
; CHECK: movwvs
%tmp = fcmp ueq float %a,%b
%retval = select i1 %tmp, i32 666, i32 42
ret i32 %retval