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Re-commit r130862 with a minor change to avoid an iterator running off the edge in some cases.

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Original message:

Teach MachineCSE how to do simple cross-block CSE involving physregs.  This allows, for example, eliminating duplicate cmpl's on x86. Part of rdar://problem/8259436 .



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130877 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2011-05-04 22:10:36 +00:00
parent b90584ae78
commit baf717a08a
3 changed files with 74 additions and 30 deletions
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78
lib/CodeGen/MachineCSE.cpp
View File

@ -33,6 +33,8 @@ STATISTIC(NumCoalesces, "Number of copies coalesced");
STATISTIC(NumCSEs, "Number of common subexpression eliminated");
STATISTIC(NumPhysCSEs,
"Number of physreg referencing common subexpr eliminated");
STATISTIC(NumCrossBlockPhysCSEs,
"Number of physreg common subexprs cross-block eliminated");
STATISTIC(NumCommutes, "Number of copies coalesced after commuting");
namespace {
@ -82,7 +84,8 @@ namespace {
MachineBasicBlock::const_iterator E) const ;
bool hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
SmallSet<unsigned,8> &PhysRefs) const;
SmallSet<unsigned,8> &PhysRefs,
SmallVector<unsigned,8> &PhysDefs) const;
bool PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
SmallSet<unsigned,8> &PhysRefs) const;
bool isCSECandidate(MachineInstr *MI);
@ -189,7 +192,8 @@ MachineCSE::isPhysDefTriviallyDead(unsigned Reg,
/// instruction does not uses a physical register.
bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
SmallSet<unsigned,8> &PhysRefs) const {
SmallSet<unsigned,8> &PhysRefs,
SmallVector<unsigned,8> &PhysDefs) 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);
@ -206,6 +210,7 @@ bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
if (MO.isDef() &&
(MO.isDead() || isPhysDefTriviallyDead(Reg, I, MBB->end())))
continue;
PhysDefs.push_back(Reg);
PhysRefs.insert(Reg);
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias)
PhysRefs.insert(*Alias);
@ -216,35 +221,43 @@ bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
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();
if (CSMI->getParent() != MBB)
return false;
MachineBasicBlock::const_iterator I = CSMI; I = llvm::next(I);
MachineBasicBlock::const_iterator E = MI;
// Look backward from MI to find CSMI.
unsigned LookAheadLeft = LookAheadLimit;
MachineBasicBlock *CurBB = MI->getParent();
MachineBasicBlock::const_reverse_iterator I(MI);
MachineBasicBlock::const_reverse_iterator E(CurBB->rend());
while (LookAheadLeft) {
// Skip over dbg_value's.
while (I != E && I->isDebugValue())
while (LookAheadLeft && I != E) {
// Skip over dbg_value's.
while (I != E && I->isDebugValue())
++I;
if (I == E) break;
if (&*I == CSMI)
return true;
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;
if (I == E)
return true;
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;
// Go back another BB; for now, only go back at most one BB.
MachineBasicBlock *CSBB = CSMI->getParent();
if (!CSBB->isSuccessor(CurBB) || CurBB->pred_size() != 1)
return false;
CurBB = CSBB;
I = CSBB->rbegin();
E = CSBB->rend();
}
return false;
@ -395,7 +408,8 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
// used, then it's not safe to replace it with a common subexpression.
// It's also not safe if the instruction uses physical registers.
SmallSet<unsigned,8> PhysRefs;
if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs)) {
SmallVector<unsigned,8> DirectPhysRefs;
if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs, DirectPhysRefs)) {
FoundCSE = false;
// ... Unless the CS is local and it also defines the physical register
@ -448,6 +462,14 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
MRI->clearKillFlags(CSEPairs[i].second);
}
MI->eraseFromParent();
if (!DirectPhysRefs.empty() && CSMI->getParent() != MBB) {
assert(CSMI->getParent()->isSuccessor(MBB));
++NumCrossBlockPhysCSEs;
SmallVector<unsigned,8>::iterator PI = DirectPhysRefs.begin(),
PE = DirectPhysRefs.end();
for (; PI != PE; ++PI)
MBB->addLiveIn(*PI);
}
++NumCSEs;
if (!PhysRefs.empty())
++NumPhysCSEs;

4
test/CodeGen/Thumb2/thumb2-cbnz.ll
View File

@ -21,8 +21,8 @@ bb7: ; preds = %bb3
bb9: ; preds = %bb7
; CHECK: cmp r0, #0
; CHECK: cmp r0, #0
; CHECK-NEXT: cbnz
; CHECK-NOT: cmp
; CHECK: cbnz
%0 = tail call double @floor(double %b) nounwind readnone ; <double> [#uses=0]
br label %bb11

22
test/CodeGen/X86/cmp-redundant.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: llc < %s -mtriple=x86_64-apple-darwin10 | FileCheck %s
define i32 @cmp(i32* %aa, i32* %bb) nounwind readnone ssp {
entry:
%a = load i32* %aa
%b = load i32* %bb
%cmp = icmp sgt i32 %a, %b
br i1 %cmp, label %return, label %if.end
; CHECK: cmp:
; CHECK: cmpl
; CHECK: jg
if.end: ; preds = %entry
; CHECK-NOT: cmpl
; CHECK: cmov
%cmp4 = icmp slt i32 %a, %b
%. = select i1 %cmp4, i32 2, i32 111
br label %return
return: ; preds = %if.end, %entry
%retval.0 = phi i32 [ 1, %entry ], [ %., %if.end ]
ret i32 %retval.0
}