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Fix the "test" optimization to recognize "dec" as an add of

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negative one, as subtracts of immediates are canonicalized
to adds.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66180 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-03-05 19:32:48 +00:00
parent 8733db351a
commit 4bfcf2a2a6
3 changed files with 31 additions and 9 deletions
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17
lib/Target/X86/X86ISelLowering.cpp
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@@ -5382,13 +5382,19 @@ SDValue X86TargetLowering::EmitTest(SDValue Op, SelectionDAG &DAG) {
UE = Op.getNode()->use_end(); UI != UE; ++UI)
if (UI->getOpcode() == ISD::STORE)
goto default_case;
// An add of one will be selected as an INC.
if (ConstantSDNode *C =
dyn_cast<ConstantSDNode>(Op.getNode()->getOperand(1)))
dyn_cast<ConstantSDNode>(Op.getNode()->getOperand(1))) {
// An add of one will be selected as an INC.
if (C->getAPIntValue() == 1) {
Opcode = X86ISD::INC;
break;
}
// An add of negative one (subtract of one) will be selected as a DEC.
if (C->getAPIntValue().isAllOnesValue()) {
Opcode = X86ISD::DEC;
break;
}
}
// Otherwise use a regular EFLAGS-setting add.
Opcode = X86ISD::ADD;
break;
@@ -5399,13 +5405,6 @@ SDValue X86TargetLowering::EmitTest(SDValue Op, SelectionDAG &DAG) {
UE = Op.getNode()->use_end(); UI != UE; ++UI)
if (UI->getOpcode() == ISD::STORE)
goto default_case;
// A subtract of one will be selected as a DEC.
if (ConstantSDNode *C =
dyn_cast<ConstantSDNode>(Op.getNode()->getOperand(1)))
if (C->getAPIntValue() == 1) {
Opcode = X86ISD::DEC;
break;
}
// Otherwise use a regular EFLAGS-setting sub.
Opcode = X86ISD::SUB;
break;