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Don't emit unneccesary branch instructions!

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llvm-svn: 5328
This commit is contained in:
Chris Lattner 2003-01-16 18:07:23 +00:00
parent 0a6ac532e1
commit bf414ca145
1 changed files with 41 additions and 15 deletions
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56
lib/Target/X86/InstSelectSimple.cpp
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@ -504,9 +504,9 @@ static unsigned getSetCCNumber(unsigned Opcode) {
case Instruction::SetEQ: return 0;
case Instruction::SetNE: return 1;
case Instruction::SetLT: return 2;
case Instruction::SetGT: return 3;
case Instruction::SetLE: return 4;
case Instruction::SetGE: return 5;
case Instruction::SetGE: return 3;
case Instruction::SetGT: return 4;
case Instruction::SetLE: return 5;
}
}
@ -515,12 +515,12 @@ static unsigned getSetCCNumber(unsigned Opcode) {
// seteq -> sete sete
// setne -> setne setne
// setlt -> setl setb
// setge -> setge setae
// setgt -> setg seta
// setle -> setle setbe
// setge -> setge setae
static const unsigned SetCCOpcodeTab[2][6] = {
{X86::SETEr, X86::SETNEr, X86::SETBr, X86::SETAr, X86::SETBEr, X86::SETAEr},
{X86::SETEr, X86::SETNEr, X86::SETLr, X86::SETGr, X86::SETLEr, X86::SETGEr},
{X86::SETEr, X86::SETNEr, X86::SETBr, X86::SETAEr, X86::SETAr, X86::SETBEr},
{X86::SETEr, X86::SETNEr, X86::SETLr, X86::SETGEr, X86::SETGr, X86::SETLEr},
};
bool ISel::EmitComparisonGetSignedness(unsigned OpNum, Value *Op0, Value *Op1) {
@ -678,14 +678,24 @@ void ISel::visitReturnInst(ReturnInst &I) {
BuildMI(BB, X86::RET, 0);
}
// getBlockAfter - Return the basic block which occurs lexically after the
// specified one.
static inline BasicBlock *getBlockAfter(BasicBlock *BB) {
Function::iterator I = BB; ++I; // Get iterator to next block
return I != BB->getParent()->end() ? &*I : 0;
}
/// visitBranchInst - Handle conditional and unconditional branches here. Note
/// that since code layout is frozen at this point, that if we are trying to
/// jump to a block that is the immediate successor of the current block, we can
/// just make a fall-through (but we don't currently).
///
void ISel::visitBranchInst(BranchInst &BI) {
if (!BI.isConditional()) {
BuildMI(BB, X86::JMP, 1).addPCDisp(BI.getSuccessor(0));
BasicBlock *NextBB = getBlockAfter(BI.getParent()); // BB after current one
if (!BI.isConditional()) { // Unconditional branch?
if (BI.getSuccessor(0) != NextBB)
BuildMI(BB, X86::JMP, 1).addPCDisp(BI.getSuccessor(0));
return;
}
@ -696,8 +706,15 @@ void ISel::visitBranchInst(BranchInst &BI) {
// computed some other way...
unsigned condReg = getReg(BI.getCondition());
BuildMI(BB, X86::CMPri8, 2).addReg(condReg).addZImm(0);
BuildMI(BB, X86::JE, 1).addPCDisp(BI.getSuccessor(1));
BuildMI(BB, X86::JMP, 1).addPCDisp(BI.getSuccessor(0));
if (BI.getSuccessor(1) == NextBB) {
if (BI.getSuccessor(0) != NextBB)
BuildMI(BB, X86::JNE, 1).addPCDisp(BI.getSuccessor(0));
} else {
BuildMI(BB, X86::JE, 1).addPCDisp(BI.getSuccessor(1));
if (BI.getSuccessor(0) != NextBB)
BuildMI(BB, X86::JMP, 1).addPCDisp(BI.getSuccessor(0));
}
return;
}
@ -710,16 +727,25 @@ void ISel::visitBranchInst(BranchInst &BI) {
// seteq -> je je
// setne -> jne jne
// setlt -> jl jb
// setge -> jge jae
// setgt -> jg ja
// setle -> jle jbe
// setge -> jge jae
static const unsigned OpcodeTab[2][6] = {
{ X86::JE, X86::JNE, X86::JB, X86::JA, X86::JBE, X86::JAE },
{ X86::JE, X86::JNE, X86::JL, X86::JG, X86::JLE, X86::JGE },
{ X86::JE, X86::JNE, X86::JB, X86::JAE, X86::JA, X86::JBE },
{ X86::JE, X86::JNE, X86::JL, X86::JGE, X86::JG, X86::JLE },
};
BuildMI(BB, OpcodeTab[isSigned][OpNum], 1).addPCDisp(BI.getSuccessor(0));
BuildMI(BB, X86::JMP, 1).addPCDisp(BI.getSuccessor(1));
if (BI.getSuccessor(0) != NextBB) {
BuildMI(BB, OpcodeTab[isSigned][OpNum], 1).addPCDisp(BI.getSuccessor(0));
if (BI.getSuccessor(1) != NextBB)
BuildMI(BB, X86::JMP, 1).addPCDisp(BI.getSuccessor(1));
} else {
// Change to the inverse condition...
if (BI.getSuccessor(1) != NextBB) {
OpNum ^= 1;
BuildMI(BB, OpcodeTab[isSigned][OpNum], 1).addPCDisp(BI.getSuccessor(1));
}
}
}