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Change this DAGCombine to build AND of SHR instead of SHR of AND; this matches the ordering we prefer in instcombine. Part of rdar://9562809.
The potential DAGCombine which enforces this more generally messes up some other very fragile patterns, so I'm leaving that alone, at least for now. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132809 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -3092,26 +3092,27 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
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}
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}
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}
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}
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// fold (shl (srl x, c1), c2) -> (shl (and x, (shl -1, c1)), (sub c2, c1)) or
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// fold (shl (srl x, c1), c2) -> (and (shl x, (sub c2, c1), MASK) or
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// (srl (and x, (shl -1, c1)), (sub c1, c2))
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// (and (srl x, (sub c1, c2), MASK)
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if (N1C && N0.getOpcode() == ISD::SRL &&
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if (N1C && N0.getOpcode() == ISD::SRL &&
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N0.getOperand(1).getOpcode() == ISD::Constant) {
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N0.getOperand(1).getOpcode() == ISD::Constant) {
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uint64_t c1 = cast<ConstantSDNode>(N0.getOperand(1))->getZExtValue();
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uint64_t c1 = cast<ConstantSDNode>(N0.getOperand(1))->getZExtValue();
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if (c1 < VT.getSizeInBits()) {
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if (c1 < VT.getSizeInBits()) {
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uint64_t c2 = N1C->getZExtValue();
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uint64_t c2 = N1C->getZExtValue();
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SDValue HiBitsMask =
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APInt Mask = APInt::getHighBitsSet(VT.getSizeInBits(),
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DAG.getConstant(APInt::getHighBitsSet(VT.getSizeInBits(),
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VT.getSizeInBits() - c1);
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VT.getSizeInBits() - c1),
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SDValue Shift;
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VT);
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if (c2 > c1) {
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SDValue Mask = DAG.getNode(ISD::AND, N0.getDebugLoc(), VT,
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Mask = Mask.shl(c2-c1);
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N0.getOperand(0),
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Shift = DAG.getNode(ISD::SHL, N->getDebugLoc(), VT, N0.getOperand(0),
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HiBitsMask);
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DAG.getConstant(c2-c1, N1.getValueType()));
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if (c2 > c1)
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} else {
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return DAG.getNode(ISD::SHL, N->getDebugLoc(), VT, Mask,
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Mask = Mask.lshr(c1-c2);
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DAG.getConstant(c2-c1, N1.getValueType()));
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Shift = DAG.getNode(ISD::SRL, N->getDebugLoc(), VT, N0.getOperand(0),
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else
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DAG.getConstant(c1-c2, N1.getValueType()));
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return DAG.getNode(ISD::SRL, N->getDebugLoc(), VT, Mask,
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}
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DAG.getConstant(c1-c2, N1.getValueType()));
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return DAG.getNode(ISD::AND, N0.getDebugLoc(), VT, Shift,
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DAG.getConstant(Mask, VT));
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}
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}
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}
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}
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// fold (shl (sra x, c1), c1) -> (and x, (shl -1, c1))
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// fold (shl (sra x, c1), c1) -> (and x, (shl -1, c1))
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11
test/CodeGen/X86/shift-pair.ll
Normal file
11
test/CodeGen/X86/shift-pair.ll
Normal file
@ -0,0 +1,11 @@
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; RUN: llc < %s -march=x86-64 | FileCheck %s
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define i64 @test(i64 %A) {
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; CHECK: @test
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; CHECK: shrq $54
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; CHECK: andq $1020
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; CHECK: ret
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%B = lshr i64 %A, 56
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%C = shl i64 %B, 2
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ret i64 %C
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}
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