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Fold immediates into compares when possible, producing "cmp $4, %eax" instead of

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loading 4 into a register and then doing the compare.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57548 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-10-15 04:13:29 +00:00
parent 709d829d3c
commit 0e13c78347
1 changed files with 36 additions and 3 deletions
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39
lib/Target/X86/X86FastISel.cpp
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@ -530,6 +530,29 @@ unsigned X86FastISel::X86ChooseCmpOpcode(MVT VT) {
return 0;
}
/// X86ChooseCmpImmediateOpcode - If we have a comparison with RHS as the RHS
/// of the comparison, return an opcode that works for the compare (e.g.
/// CMP32ri) otherwise return 0.
static unsigned X86ChooseCmpImmediateOpcode(ConstantInt *RHSC) {
if (RHSC == 0) return 0;
if (RHSC->getType() == Type::Int8Ty)
return X86::CMP8ri;
if (RHSC->getType() == Type::Int16Ty)
return X86::CMP16ri;
if (RHSC->getType() == Type::Int32Ty)
return X86::CMP32ri;
// 64-bit comparisons are only valid if the immediate fits in a 32-bit sext
// field.
if (RHSC->getType() == Type::Int64Ty &&
(int)RHSC->getSExtValue() == RHSC->getSExtValue())
return X86::CMP64ri32;
// Otherwise, we can't fold the immediate into this comparison.
return 0;
}
bool X86FastISel::X86SelectCmp(Instruction *I) {
CmpInst *CI = cast<CmpInst>(I);
@ -676,10 +699,20 @@ bool X86FastISel::X86SelectBranch(Instruction *I) {
if (CompareOpc == 0) return false;
unsigned Op0Reg = getRegForValue(Op0);
if (Op0Reg == 0) return false;
unsigned Op1Reg = getRegForValue(Op1);
if (Op1Reg == 0) return false;
BuildMI(MBB, TII.get(CompareOpc)).addReg(Op0Reg).addReg(Op1Reg);
// We have two options: compare with register or immediate. If the RHS of
// the compare is an immediate that we can fold into this compare, use
// CMPri, otherwise use CMPrr.
ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1);
if (unsigned CompareImmOpc = X86ChooseCmpImmediateOpcode(Op1C)) {
BuildMI(MBB, TII.get(CompareOpc)).addReg(Op0Reg)
.addImm(Op1C->getSExtValue());
} else {
unsigned Op1Reg = getRegForValue(Op1);
if (Op1Reg == 0) return false;
BuildMI(MBB, TII.get(CompareOpc)).addReg(Op0Reg).addReg(Op1Reg);
}
BuildMI(MBB, TII.get(BranchOpc)).addMBB(TrueMBB);
FastEmitBranch(FalseMBB);
MBB->addSuccessor(TrueMBB);