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Match this pattern so that we can generate simpler code:

Browse Source 
%a = ...
  %b = and i32 %a, 2
  %c = srl i32 %b, 1
  %d = br i32 %c, 

into

  %a = ...
  %b = and %a, 2
  %c = X86ISD::CMP %b, 0
  %d = X86ISD::BRCOND %c ...

This applies only when the AND constant value has one bit set and the SRL
constant is equal to the log2 of the AND constant. The back-end is smart enough
to convert the result into a TEST/JMP sequence.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67728 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2009-03-26 01:47:50 +00:00
parent bddc442a00
commit 8b4b874cc6
1 changed files with 39 additions and 0 deletions
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39
lib/Target/X86/X86ISelLowering.cpp
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@ -5870,6 +5870,45 @@ SDValue X86TargetLowering::LowerBRCOND(SDValue Op, SelectionDAG &DAG) {
CC = DAG.getConstant(CCode, MVT::i8);
Cond = Cond.getOperand(0).getOperand(1);
addTest = false;
} else if (Cond.hasOneUse() && Cond.getOpcode() == ISD::SRL) {
// Match this pattern so that we can generate simpler code:
//
// %a = ...
// %b = and i32 %a, 2
// %c = srl i32 %b, 1
// %d = br i32 %c,
//
// into
//
// %a = ...
// %b = and %a, 2
// %c = X86ISD::CMP %b, 0
// %d = X86ISD::BRCOND %c ...
//
// This applies only when the AND constant value has one bit set and the
// SRL constant is equal to the log2 of the AND constant. The back-end is
// smart enough to convert the result into a TEST/JMP sequence.
SDValue Op0 = Cond.getOperand(0);
SDValue Op1 = Cond.getOperand(1);
if (Op0.getOpcode() == ISD::AND &&
Op0.hasOneUse() &&
Op1.getOpcode() == ISD::Constant) {
SDValue AndOp0 = Op0.getOperand(0);
SDValue AndOp1 = Op0.getOperand(1);
if (AndOp1.getOpcode() == ISD::Constant) {
const APInt &AndConst = cast<ConstantSDNode>(AndOp1)->getAPIntValue();
if (AndConst.isPowerOf2() &&
cast<ConstantSDNode>(Op1)->getAPIntValue()==AndConst.logBase2()) {
CC = DAG.getConstant(X86::COND_NE, MVT::i8);
Cond = EmitTest(Op0, X86::COND_NE, DAG);
return DAG.getNode(X86ISD::BRCOND, dl, Op.getValueType(),
Chain, Dest, CC, Cond);
}
}
}
}
}