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Revert "[ValueTracking] Improve ValueTracking on left shift with nsw flag"
This reverts commit r278172. It causes PR28946. llvm-svn: 278740
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@ -1064,22 +1064,13 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
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}
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case Instruction::Shl: {
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// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
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bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
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auto KZF = [BitWidth, NSW](const APInt &KnownZero, unsigned ShiftAmt) {
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APInt KZResult = (KnownZero << ShiftAmt) |
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auto KZF = [BitWidth](const APInt &KnownZero, unsigned ShiftAmt) {
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return (KnownZero << ShiftAmt) |
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APInt::getLowBitsSet(BitWidth, ShiftAmt); // Low bits known 0.
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// If this shift has "nsw" keyword, then the result is either a poison
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// value or has the same sign bit as the first operand.
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if (NSW && KnownZero.isNegative())
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KZResult.setBit(BitWidth - 1);
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return KZResult;
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};
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auto KOF = [BitWidth, NSW](const APInt &KnownOne, unsigned ShiftAmt) {
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APInt KOResult = KnownOne << ShiftAmt;
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if (NSW && KnownOne.isNegative())
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KOResult.setBit(BitWidth - 1);
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return KOResult;
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auto KOF = [BitWidth](const APInt &KnownOne, unsigned ShiftAmt) {
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return KnownOne << ShiftAmt;
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};
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computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne,
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@ -1,24 +0,0 @@
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; RUN: opt < %s -instcombine -S | FileCheck %s
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; Result of left shifting a non-negative integer
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; with nsw flag should also be non-negative
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define i1 @test_shift_nonnegative(i32 %a) {
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; CHECK-LABEL: @test_shift_nonnegative(
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; CHECK: ret i1 true
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%b = lshr i32 %a, 2
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%shift = shl nsw i32 %b, 3
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%cmp = icmp sge i32 %shift, 0
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ret i1 %cmp
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}
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; Result of left shifting a negative integer with
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; nsw flag should also be negative
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define i1 @test_shift_negative(i32 %a, i32 %b) {
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; CHECK-LABEL: @test_shift_negative(
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; CHECK: ret i1 true
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%c = or i32 %a, -2147483648
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%d = and i32 %b, 7
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%shift = shl nsw i32 %c, %d
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%cmp = icmp slt i32 %shift, 0
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ret i1 %cmp
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}
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