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teach instcombine to delete sign extending shift pairs (sra(shl X, C), C) when
the input is already sign extended. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93019 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -414,17 +414,28 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
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if (Instruction *R = commonShiftTransforms(I))
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return R;
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Value *Op0 = I.getOperand(0);
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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// ashr int -1, X = -1 (for any arithmetic shift rights of ~0)
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if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0))
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if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0)) {
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// ashr int -1, X = -1 (for any arithmetic shift rights of ~0)
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if (CSI->isAllOnesValue())
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return ReplaceInstUsesWith(I, CSI);
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}
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if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
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// If the input is a SHL by the same constant (ashr (shl X, C), C), then we
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// have a sign-extend idiom. If the input value is known to already be sign
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// extended enough, delete the extension.
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Value *X;
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if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1))) &&
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ComputeNumSignBits(X) > Op1C->getZExtValue())
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return ReplaceInstUsesWith(I, X);
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}
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// See if we can turn a signed shr into an unsigned shr.
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if (MaskedValueIsZero(Op0,
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APInt::getSignBit(I.getType()->getScalarSizeInBits())))
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return BinaryOperator::CreateLShr(Op0, I.getOperand(1));
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return BinaryOperator::CreateLShr(Op0, Op1);
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// Arithmetic shifting an all-sign-bit value is a no-op.
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unsigned NumSignBits = ComputeNumSignBits(Op0);
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@ -37,3 +37,22 @@ C:
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; CHECK: %P = phi i64
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; CHECK-NEXT: ret i64 %P
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}
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define i64 @test4(i1 %X, i64 %Y, i1 %Cond) {
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br i1 %Cond, label %T, label %F
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T:
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%X2 = sext i1 %X to i64
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br label %C
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F:
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%Y2 = ashr i64 %Y, 63
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br label %C
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C:
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%P = phi i64 [%X2, %T], [%Y2, %F]
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%R = shl i64 %P, 12
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%S = ashr i64 %R, 12
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ret i64 %S
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; CHECK: @test4
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; CHECK: %P = phi i64
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; CHECK-NEXT: ret i64 %P
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}
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