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Optimize conditional branches in X86FastISel. This replaces

Browse Source 
sequences like this:
       sete    %al
       testb   %al, %al
       jne     LBB11_1
with this:
       je      LBB11_1

llvm-svn: 56969
This commit is contained in:
Dan Gohman 2008-10-02 22:15:21 +00:00
parent bf63ae1e29
commit e75d14f8b0
3 changed files with 166 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/llvm/CodeGen/FastISel.h
View File

@ -238,6 +238,11 @@ protected:
/// from a specified index of a superregister.
unsigned FastEmitInst_extractsubreg(unsigned Op0, uint32_t Idx);
/// FastEmitBranch - Emit an unconditional branch to the given block,
/// unless it is the immediate (fall-through) successor, and update
/// the CFG.
void FastEmitBranch(MachineBasicBlock *MBB);
void UpdateValueMap(Value* I, unsigned Reg);
unsigned createResultReg(const TargetRegisterClass *RC);

28
lib/CodeGen/SelectionDAG/FastISel.cpp
View File

@ -461,6 +461,23 @@ FastISel::SelectInstruction(Instruction *I) {
return SelectOperator(I, I->getOpcode());
}
/// FastEmitBranch - Emit an unconditional branch to the given block,
/// unless it is the immediate (fall-through) successor, and update
/// the CFG.
void
FastISel::FastEmitBranch(MachineBasicBlock *MSucc) {
MachineFunction::iterator NextMBB =
next(MachineFunction::iterator(MBB));
if (MBB->isLayoutSuccessor(MSucc)) {
// The unconditional fall-through case, which needs no instructions.
} else {
// The unconditional branch case.
TII.InsertBranch(*MBB, MSucc, NULL, SmallVector<MachineOperand, 0>());
}
MBB->addSuccessor(MSucc);
}
bool
FastISel::SelectOperator(User *I, unsigned Opcode) {
switch (Opcode) {
@ -508,18 +525,9 @@ FastISel::SelectOperator(User *I, unsigned Opcode) {
BranchInst *BI = cast<BranchInst>(I);
if (BI->isUnconditional()) {
MachineFunction::iterator NextMBB =
next(MachineFunction::iterator(MBB));
BasicBlock *LLVMSucc = BI->getSuccessor(0);
MachineBasicBlock *MSucc = MBBMap[LLVMSucc];
if (NextMBB != MF.end() && MSucc == NextMBB) {
// The unconditional fall-through case, which needs no instructions.
} else {
// The unconditional branch case.
TII.InsertBranch(*MBB, MSucc, NULL, SmallVector<MachineOperand, 0>());
}
MBB->addSuccessor(MSucc);
FastEmitBranch(MSucc);
return true;
}

160
lib/Target/X86/X86FastISel.cpp
View File

@ -90,6 +90,8 @@ private:
bool X86SelectSelect(Instruction *I);
bool X86SelectTrunc(Instruction *I);
unsigned X86ChooseCmpOpcode(MVT VT);
bool X86SelectFPExt(Instruction *I);
bool X86SelectFPTrunc(Instruction *I);
@ -507,6 +509,19 @@ bool X86FastISel::X86SelectLoad(Instruction *I) {
return false;
}
unsigned X86FastISel::X86ChooseCmpOpcode(MVT VT) {
switch (VT.getSimpleVT()) {
case MVT::i8: return X86::CMP8rr;
case MVT::i16: return X86::CMP16rr;
case MVT::i32: return X86::CMP32rr;
case MVT::i64: return X86::CMP64rr;
case MVT::f32: return X86::UCOMISSrr;
case MVT::f64: return X86::UCOMISDrr;
default: break;
}
return 0;
}
bool X86FastISel::X86SelectCmp(Instruction *I) {
CmpInst *CI = cast<CmpInst>(I);
@ -519,16 +534,7 @@ bool X86FastISel::X86SelectCmp(Instruction *I) {
unsigned Op1Reg = getRegForValue(CI->getOperand(1));
if (Op1Reg == 0) return false;
unsigned Opc;
switch (VT.getSimpleVT()) {
case MVT::i8: Opc = X86::CMP8rr; break;
case MVT::i16: Opc = X86::CMP16rr; break;
case MVT::i32: Opc = X86::CMP32rr; break;
case MVT::i64: Opc = X86::CMP64rr; break;
case MVT::f32: Opc = X86::UCOMISSrr; break;
case MVT::f64: Opc = X86::UCOMISDrr; break;
default: return false;
}
unsigned Opc = X86ChooseCmpOpcode(VT);
unsigned ResultReg = createResultReg(&X86::GR8RegClass);
switch (CI->getPredicate()) {
@ -661,19 +667,139 @@ bool X86FastISel::X86SelectZExt(Instruction *I) {
}
bool X86FastISel::X86SelectBranch(Instruction *I) {
BranchInst *BI = cast<BranchInst>(I);
// Unconditional branches are selected by tablegen-generated code.
unsigned OpReg = getRegForValue(BI->getCondition());
if (OpReg == 0) return false;
// Handle a conditional branch.
BranchInst *BI = cast<BranchInst>(I);
MachineBasicBlock *TrueMBB = MBBMap[BI->getSuccessor(0)];
MachineBasicBlock *FalseMBB = MBBMap[BI->getSuccessor(1)];
BuildMI(MBB, TII.get(X86::TEST8rr)).addReg(OpReg).addReg(OpReg);
BuildMI(MBB, TII.get(X86::JNE)).addMBB(TrueMBB);
BuildMI(MBB, TII.get(X86::JMP)).addMBB(FalseMBB);
// Fold the common case of a conditional branch with a comparison.
if (CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition())) {
if (CI->hasOneUse()) {
MVT VT = TLI.getValueType(CI->getOperand(0)->getType());
unsigned Opc = X86ChooseCmpOpcode(VT);
if (Opc == 0) return false;
// Try to take advantage of fallthrough opportunities.
CmpInst::Predicate Predicate = CI->getPredicate();
if (MBB->isLayoutSuccessor(TrueMBB)) {
std::swap(TrueMBB, FalseMBB);
Predicate = CmpInst::getInversePredicate(Predicate);
}
unsigned Op0Reg = getRegForValue(CI->getOperand(0));
if (Op0Reg == 0) return false;
unsigned Op1Reg = getRegForValue(CI->getOperand(1));
if (Op1Reg == 0) return false;
switch (Predicate) {
case CmpInst::FCMP_OGT:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JA)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_OGE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JAE)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_OLT:
BuildMI(MBB, TII.get(Opc)).addReg(Op1Reg).addReg(Op0Reg);
BuildMI(MBB, TII.get(X86::JA)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_OLE:
BuildMI(MBB, TII.get(Opc)).addReg(Op1Reg).addReg(Op0Reg);
BuildMI(MBB, TII.get(X86::JAE)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_ONE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JNE)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_ORD:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JNP)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_UNO:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JP)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_UEQ:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JE)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_UGT:
BuildMI(MBB, TII.get(Opc)).addReg(Op1Reg).addReg(Op0Reg);
BuildMI(MBB, TII.get(X86::JB)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_UGE:
BuildMI(MBB, TII.get(Opc)).addReg(Op1Reg).addReg(Op0Reg);
BuildMI(MBB, TII.get(X86::JBE)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_ULT:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JB)).addMBB(TrueMBB);
break;
case CmpInst::FCMP_ULE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JBE)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_EQ:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JE)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_NE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JNE)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_UGT:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JA)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_UGE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JAE)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_ULT:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JB)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_ULE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JBE)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_SGT:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JG)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_SGE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JGE)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_SLT:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JL)).addMBB(TrueMBB);
break;
case CmpInst::ICMP_SLE:
BuildMI(MBB, TII.get(Opc)).addReg(Op0Reg).addReg(Op1Reg);
BuildMI(MBB, TII.get(X86::JLE)).addMBB(TrueMBB);
break;
default:
return false;
}
MBB->addSuccessor(TrueMBB);
FastEmitBranch(FalseMBB);
return true;
}
}
// Otherwise do a clumsy setcc and re-test it.
unsigned OpReg = getRegForValue(BI->getCondition());
if (OpReg == 0) return false;
BuildMI(MBB, TII.get(X86::TEST8rr)).addReg(OpReg).addReg(OpReg);
BuildMI(MBB, TII.get(X86::JNE)).addMBB(TrueMBB);
MBB->addSuccessor(TrueMBB);
MBB->addSuccessor(FalseMBB);
FastEmitBranch(FalseMBB);
return true;
}