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[X86] ISEL (and X, <constant mask>) to BZHI when BMI2 is available.

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Generating BZHI in the variable mask case, i.e. (and X, (sub (shl 1, N), 1)),
was already supported, but we were missing the constant-mask case. This patch
fixes that.

<rdar://problem/15480077>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206738 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Lang Hames
2014-04-21 08:18:53 +00:00
parent a21cd0433e
commit f69bb5e43c
2 changed files with 32 additions and 0 deletions
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14
lib/Target/X86/X86ISelLowering.cpp
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@@ -18503,6 +18503,20 @@ static SDValue PerformAndCombine(SDNode *N, SelectionDAG &DAG,
}
} // BEXTR
// Check for BZHI with contiguous mask: (and X, 0x0..0f..f)
// This should be checked after BEXTR - when X is a shift, a BEXTR is
// preferrable.
if (Subtarget->hasBMI2()) {
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N1)) {
uint64_t Mask = C->getZExtValue();
if (isMask_64(Mask)) {
unsigned LZ = CountTrailingOnes_64(Mask);
return DAG.getNode(X86ISD::BZHI, DL, VT, N0,
DAG.getConstant(LZ, MVT::i8));
}
}
}
return SDValue();
}