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This is another case where instcombine demanded bits optimization created

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large immediates. Add dag combine logic to recover in case the large
immediates doesn't fit in cmp immediate operand field.

int foo(unsigned long l) {
  return (l>> 47) == 1;
}

we produce

  %shr.mask = and i64 %l, -140737488355328
  %cmp = icmp eq i64 %shr.mask, 140737488355328
  %conv = zext i1 %cmp to i32
  ret i32 %conv

which codegens to

movq    $0xffff800000000000,%rax
andq    %rdi,%rax
movq    $0x0000800000000000,%rcx
cmpq    %rcx,%rax
sete    %al
movzbl    %al,%eax
ret

TargetLowering::SimplifySetCC would transform
(X & -256) == 256 -> (X >> 8) == 1
if the immediate fails the isLegalICmpImmediate() test. For x86,
that's immediates which are not a signed 32-bit immediate.

Based on a patch by Eli Friedman.

PR10328
rdar://9758774


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160346 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2012-07-17 06:53:39 +00:00
parent 06a27cc1aa
commit 70e10d3fe4
4 changed files with 58 additions and 4 deletions
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21
lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -2322,6 +2322,27 @@ TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
}
}
}
if (!isLegalICmpImmediate(C1.getSExtValue())) {
// (X & -256) == 256 -> (X >> 8) == 1
if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
N0.getOpcode() == ISD::AND && N0.hasOneUse()) {
if (ConstantSDNode *AndRHS =
dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
const APInt &AndRHSC = AndRHS->getAPIntValue();
if ((-AndRHSC).isPowerOf2() && (AndRHSC & C1) == C1) {
unsigned ShiftBits = AndRHSC.countTrailingZeros();
EVT ShiftTy = DCI.isBeforeLegalize() ?
getPointerTy() : getShiftAmountTy(N0.getValueType());
EVT CmpTy = N0.getValueType();
SDValue Shift = DAG.getNode(ISD::SRL, dl, CmpTy, N0.getOperand(0),
DAG.getConstant(ShiftBits, ShiftTy));
SDValue CmpRHS = DAG.getConstant(C1.lshr(ShiftBits), CmpTy);
return DAG.getSetCC(dl, VT, Shift, CmpRHS, Cond);
}
}
}
}
}
if (isa<ConstantFPSDNode>(N0.getNode())) {