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[GlobalISel] Add computeNumSignBits for SHL (#152067)
This patch ports the `ISD::SHL` handling from SelectionDAG’s `ComputeNumSignBits` to GlobalISel. Related to #150515.
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‎llvm/lib/CodeGen/GlobalISel/GISelValueTracking.cpp‎

Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1892,6 +1892,44 @@ unsigned GISelValueTracking::computeNumSignBits(Register R,
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FirstAnswer = std::min<uint64_t>(FirstAnswer + *C, TyBits);
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break;
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}
1895+
case TargetOpcode::G_SHL: {
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Register Src1 = MI.getOperand(1).getReg();
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Register Src2 = MI.getOperand(2).getReg();
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if (std::optional<ConstantRange> ShAmtRange =
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getValidShiftAmountRange(Src2, DemandedElts, Depth + 1)) {
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uint64_t MaxShAmt = ShAmtRange->getUnsignedMax().getZExtValue();
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uint64_t MinShAmt = ShAmtRange->getUnsignedMin().getZExtValue();
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MachineInstr &ExtMI = *MRI.getVRegDef(Src1);
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unsigned ExtOpc = ExtMI.getOpcode();
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// Try to look through ZERO/SIGN/ANY_EXTEND. If all extended bits are
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// shifted out, then we can compute the number of sign bits for the
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// operand being extended. A future improvement could be to pass along the
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// "shifted left by" information in the recursive calls to
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// ComputeKnownSignBits. Allowing us to handle this more generically.
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if (ExtOpc == TargetOpcode::G_SEXT || ExtOpc == TargetOpcode::G_ZEXT ||
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ExtOpc == TargetOpcode::G_ANYEXT) {
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LLT ExtTy = MRI.getType(Src1);
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Register Extendee = ExtMI.getOperand(1).getReg();
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LLT ExtendeeTy = MRI.getType(Extendee);
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uint64_t SizeDiff =
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ExtTy.getScalarSizeInBits() - ExtendeeTy.getScalarSizeInBits();
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1919+
if (SizeDiff <= MinShAmt) {
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unsigned Tmp =
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SizeDiff + computeNumSignBits(Extendee, DemandedElts, Depth + 1);
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if (MaxShAmt < Tmp)
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return Tmp - MaxShAmt;
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}
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}
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// shl destroys sign bits, ensure it doesn't shift out all sign bits.
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unsigned Tmp = computeNumSignBits(Src1, DemandedElts, Depth + 1);
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if (MaxShAmt < Tmp)
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return Tmp - MaxShAmt;
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}
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break;
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}
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case TargetOpcode::G_TRUNC: {
18961934
Register Src = MI.getOperand(1).getReg();
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LLT SrcTy = MRI.getType(Src);

‎llvm/test/CodeGen/AArch64/GlobalISel/knownbits-shl.mir‎

Lines changed: 242 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,242 @@
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# NOTE: Assertions have been autogenerated by utils/update_givaluetracking_test_checks.py UTC_ARGS: --version 5
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# RUN: llc -mtriple aarch64 -passes="print<gisel-value-tracking>" %s -o - 2>&1 | FileCheck %s
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---
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name: Cst
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body: |
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bb.1:
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; CHECK-LABEL: name: @Cst
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; CHECK-NEXT: %0:_ KnownBits:11100000 SignBits:3
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; CHECK-NEXT: %1:_ KnownBits:00000010 SignBits:6
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; CHECK-NEXT: %2:_ KnownBits:10000000 SignBits:1
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%0:_(s8) = G_CONSTANT i8 224
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%1:_(s8) = G_CONSTANT i8 2
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%2:_(s8) = G_SHL %0, %1
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...
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---
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name: CstBig
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body: |
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bb.1:
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; CHECK-LABEL: name: @CstBig
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; CHECK-NEXT: %0:_ KnownBits:11111001 SignBits:5
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; CHECK-NEXT: %1:_ KnownBits:00000110 SignBits:5
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; CHECK-NEXT: %2:_ KnownBits:01000000 SignBits:1
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%0:_(s8) = G_CONSTANT i8 249
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%1:_(s8) = G_CONSTANT i8 6
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%2:_(s8) = G_SHL %0, %1
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...
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---
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name: CstSext
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body: |
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bb.1:
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; CHECK-LABEL: name: @CstSext
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; CHECK-NEXT: %0:_ KnownBits:10000001 SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:00000100 SignBits:5
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; CHECK-NEXT: %2:_ KnownBits:11111000 SignBits:5
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; CHECK-NEXT: %3:_ KnownBits:00000011 SignBits:6
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; CHECK-NEXT: %4:_ KnownBits:11000000 SignBits:2
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%0:_(s8) = G_CONSTANT i8 129
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%1:_(s8) = G_CONSTANT i8 4
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%2:_(s8) = G_ASHR %0, %1
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%3:_(s8) = G_CONSTANT i8 3
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%4:_(s8) = G_SHL %2, %3
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...
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---
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name: CstSextBig
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body: |
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bb.1:
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; CHECK-LABEL: name: @CstSextBig
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; CHECK-NEXT: %0:_ KnownBits:10000001 SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:00000100 SignBits:5
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; CHECK-NEXT: %2:_ KnownBits:11111000 SignBits:5
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; CHECK-NEXT: %3:_ KnownBits:00000110 SignBits:5
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; CHECK-NEXT: %4:_ KnownBits:00000000 SignBits:8
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%0:_(s8) = G_CONSTANT i8 129
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%1:_(s8) = G_CONSTANT i8 4
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%2:_(s8) = G_ASHR %0, %1
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%3:_(s8) = G_CONSTANT i8 6
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%4:_(s8) = G_SHL %2, %3
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...
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---
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name: ScalarVar
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body: |
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bb.1:
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; CHECK-LABEL: name: @ScalarVar
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; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %2:_ KnownBits:???????? SignBits:1
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%0:_(s8) = COPY $b0
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%1:_(s8) = COPY $b1
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%2:_(s8) = G_SHL %0, %1
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...
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---
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name: ScalarCst
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body: |
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bb.1:
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; CHECK-LABEL: name: @ScalarCst
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; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:00000011 SignBits:6
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; CHECK-NEXT: %2:_ KnownBits:?????000 SignBits:1
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%0:_(s8) = COPY $b0
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%1:_(s8) = G_CONSTANT i8 3
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%2:_(s8) = G_SHL %0, %1
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...
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---
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name: VectorVar
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body: |
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bb.1:
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; CHECK-LABEL: name: @VectorVar
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; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:1
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; CHECK-NEXT: %2:_ KnownBits:???????????????? SignBits:1
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%0:_(<4 x s16>) = COPY $d0
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%1:_(<4 x s16>) = COPY $d1
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%2:_(<4 x s16>) = G_SHL %0, %1
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...
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---
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name: VectorCst
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body: |
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bb.1:
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; CHECK-LABEL: name: @VectorCst
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; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %2:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %3:_ KnownBits:?????????????000 SignBits:1
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%0:_(<4 x s16>) = COPY $d0
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%1:_(s16) = G_CONSTANT i16 3
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%2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
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%3:_(<4 x s16>) = G_SHL %0, %2
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...
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---
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name: VectorCst36
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body: |
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bb.1:
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; CHECK-LABEL: name: @VectorCst36
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; CHECK-NEXT: %0:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %1:_ KnownBits:0000000000000110 SignBits:13
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; CHECK-NEXT: %2:_ KnownBits:0000000000000?1? SignBits:13
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; CHECK-NEXT: %3:_ KnownBits:0000000000000?1? SignBits:13
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; CHECK-NEXT: %4:_ KnownBits:000000????????00 SignBits:7
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%0:_(s16) = G_CONSTANT i16 3
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%1:_(s16) = G_CONSTANT i16 6
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%2:_(<4 x s16>) = G_BUILD_VECTOR %0, %1, %1, %0
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%3:_(<4 x s16>) = G_BUILD_VECTOR %0, %1, %1, %0
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%4:_(<4 x s16>) = G_SHL %2, %3
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...
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---
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name: VectorCst3unknown
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body: |
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bb.1:
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; CHECK-LABEL: name: @VectorCst3unknown
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; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:1
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; CHECK-NEXT: %2:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %3:_ KnownBits:???????????????? SignBits:1
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; CHECK-NEXT: %4:_ KnownBits:???????????????? SignBits:1
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%0:_(<4 x s16>) = COPY $d0
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%2:_(s16) = COPY $h0
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%1:_(s16) = G_CONSTANT i16 3
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%3:_(<4 x s16>) = G_BUILD_VECTOR %1, %2, %2, %1
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%4:_(<4 x s16>) = G_SHL %0, %3
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...
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---
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name: VectorSext
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body: |
146+
bb.1:
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; CHECK-LABEL: name: @VectorSext
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; CHECK-NEXT: %0:_ KnownBits:11101110 SignBits:3
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; CHECK-NEXT: %1:_ KnownBits:1111111111101110 SignBits:11
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; CHECK-NEXT: %2:_ KnownBits:1111111111101110 SignBits:11
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; CHECK-NEXT: %3:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %4:_ KnownBits:0000000000000110 SignBits:13
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; CHECK-NEXT: %5:_ KnownBits:0000000000000?1? SignBits:13
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; CHECK-NEXT: %6:_ KnownBits:1111??11?????000 SignBits:5
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%0:_(s8) = G_CONSTANT i8 238
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%1:_(s16) = G_SEXT %0(s8)
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%2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
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%3:_(s16) = G_CONSTANT i16 3
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%4:_(s16) = G_CONSTANT i16 6
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%5:_(<4 x s16>) = G_BUILD_VECTOR %3, %4, %4, %3
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%6:_(<4 x s16>) = G_SHL %2, %5
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...
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---
164+
name: VectorSextBig
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body: |
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bb.1:
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; CHECK-LABEL: name: @VectorSextBig
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; CHECK-NEXT: %0:_ KnownBits:11101110 SignBits:3
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; CHECK-NEXT: %1:_ KnownBits:1111111111101110 SignBits:11
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; CHECK-NEXT: %2:_ KnownBits:1111111111101110 SignBits:11
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; CHECK-NEXT: %3:_ KnownBits:0000000000001000 SignBits:12
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; CHECK-NEXT: %4:_ KnownBits:0000000000001001 SignBits:12
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; CHECK-NEXT: %5:_ KnownBits:000000000000100? SignBits:12
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; CHECK-NEXT: %6:_ KnownBits:11??11?000000000 SignBits:2
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%0:_(s8) = G_CONSTANT i8 238
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%1:_(s16) = G_SEXT %0(s8)
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%2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
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%3:_(s16) = G_CONSTANT i16 8
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%4:_(s16) = G_CONSTANT i16 9
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%5:_(<4 x s16>) = G_BUILD_VECTOR %3, %4, %4, %3
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%6:_(<4 x s16>) = G_SHL %2, %5
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...
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---
184+
name: SHLless
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body: |
186+
bb.1:
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; CHECK-LABEL: name: @SHLless
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; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:9
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; CHECK-NEXT: %2:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %3:_ KnownBits:?????????????000 SignBits:6
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%0:_(s8) = COPY $b0
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%1:_(s16) = G_SEXT %0(s8)
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%2:_(s16) = G_CONSTANT i16 3
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%3:_(s16) = G_SHL %1, %2
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...
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---
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name: SHLeq
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body: |
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bb.1:
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; CHECK-LABEL: name: @SHLeq
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; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:9
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; CHECK-NEXT: %2:_ KnownBits:0000000000001000 SignBits:12
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; CHECK-NEXT: %3:_ KnownBits:????????00000000 SignBits:1
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%0:_(s8) = COPY $b0
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%1:_(s16) = G_SEXT %0(s8)
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%2:_(s16) = G_CONSTANT i16 8
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%3:_(s16) = G_SHL %1, %2
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...
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---
212+
name: SHLmore
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body: |
214+
bb.1:
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; CHECK-LABEL: name: @SHLmore
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; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:9
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; CHECK-NEXT: %2:_ KnownBits:0000000000001101 SignBits:12
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; CHECK-NEXT: %3:_ KnownBits:???0000000000000 SignBits:1
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%0:_(s8) = COPY $b0
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%1:_(s16) = G_SEXT %0(s8)
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%2:_(s16) = G_CONSTANT i16 13
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%3:_(s16) = G_SHL %1, %2
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...
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---
226+
name: SignBitsThroughZext
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body: |
228+
bb.1:
229+
; CHECK-LABEL: name: @SignBitsThroughZext
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; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
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; CHECK-NEXT: %1:_ KnownBits:0000000000000011 SignBits:14
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; CHECK-NEXT: %2:_ KnownBits:???????? SignBits:4
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; CHECK-NEXT: %3:_ KnownBits:00000000???????? SignBits:8
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; CHECK-NEXT: %4:_ KnownBits:0000000000001000 SignBits:12
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; CHECK-NEXT: %5:_ KnownBits:????????00000000 SignBits:4
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%0:_(s8) = COPY $b0
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%1:_(s16) = G_CONSTANT i16 3
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%2:_(s8) = G_ASHR %0, %1
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%3:_(s16) = G_ZEXT %2
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%4:_(s16) = G_CONSTANT i16 8
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%5:_(s16) = G_SHL %3, %4
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...

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