[GlobalISel] Add G_ADD for computeNumSignBits #159202
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backend:AArch64
llvm:globalisel
llvm:SelectionDAG
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@llvm/pr-subscribers-llvm-selectiondag @llvm/pr-subscribers-backend-aarch64 Author: Yatao Wang (ningxinr) ChangesThis patch ports the ISD::ADD handling from SelectionDAG’s ComputeNumSignBits to GlobalISel. Related to #150515. Full diff: https://github.com/llvm/llvm-project/pull/159202.diff 4 Files Affected:
diff --git a/llvm/lib/CodeGen/GlobalISel/GISelValueTracking.cpp b/llvm/lib/CodeGen/GlobalISel/GISelValueTracking.cpp
index 9b4c103763d74..c904a351be060 100644
--- a/llvm/lib/CodeGen/GlobalISel/GISelValueTracking.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/GISelValueTracking.cpp
@@ -1951,6 +1951,41 @@ unsigned GISelValueTracking::computeNumSignBits(Register R,
break;
}
+ case TargetOpcode::G_ADD: {
+ Register Src1 = MI.getOperand(1).getReg();
+ unsigned Src1NumSignBits =
+ computeNumSignBits(Src1, DemandedElts, Depth + 1);
+ if (Src1NumSignBits == 1)
+ return 1; // Early Out.
+
+ Register Src2 = MI.getOperand(2).getReg();
+ unsigned Src2NumSignBits =
+ computeNumSignBits(Src2, DemandedElts, Depth + 1);
+ if (Src2NumSignBits == 1)
+ return 1; // Early out.
+
+ // Special case decrementing a value (ADD X, -1):
+ KnownBits Known2 = getKnownBits(Src2, DemandedElts, Depth);
+ if (Known2.One.isAllOnes()) {
+ KnownBits Known1 = getKnownBits(Src1, DemandedElts, Depth);
+ // If the input is known to be 0 or 1, the output is 0/-1, which is all
+ // sign bits set.
+ if ((Known1.Zero | 1).isAllOnes())
+ return TyBits;
+
+ // If the input is known to be positive (the sign bit is known clear),
+ // the output of the NEG has the same number of sign bits as the input.
+ if (Known1.isNonNegative())
+ return Src1NumSignBits;
+
+ // Otherwise, we treat this like an ADD.
+ }
+
+ // Add can have at most one carry bit. Thus we know that the output
+ // is, at worst, one more bit than the inputs.
+ FirstAnswer = std::min(Src1NumSignBits, Src2NumSignBits) - 1;
+ break;
+ }
case TargetOpcode::G_FCMP:
case TargetOpcode::G_ICMP: {
bool IsFP = Opcode == TargetOpcode::G_FCMP;
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index bcf25958d0982..fa34db8de5260 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5039,10 +5039,13 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
break;
case ISD::ADD:
case ISD::ADDC:
- // Add can have at most one carry bit. Thus we know that the output
- // is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(Op.getOperand(0), DemandedElts, Depth + 1);
- if (Tmp == 1) return 1; // Early out.
+ if (Tmp == 1)
+ return 1; // Early out.
+
+ Tmp2 = ComputeNumSignBits(Op.getOperand(1), DemandedElts, Depth + 1);
+ if (Tmp2 == 1)
+ return 1; // Early out.
// Special case decrementing a value (ADD X, -1):
if (ConstantSDNode *CRHS =
@@ -5062,8 +5065,8 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
return Tmp;
}
- Tmp2 = ComputeNumSignBits(Op.getOperand(1), DemandedElts, Depth + 1);
- if (Tmp2 == 1) return 1; // Early out.
+ // Add can have at most one carry bit. Thus we know that the output
+ // is, at worst, one more bit than the inputs.
return std::min(Tmp, Tmp2) - 1;
case ISD::SUB:
Tmp2 = ComputeNumSignBits(Op.getOperand(1), DemandedElts, Depth + 1);
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/knownbits-add.mir b/llvm/test/CodeGen/AArch64/GlobalISel/knownbits-add.mir
new file mode 100644
index 0000000000000..f4f057e92633f
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/knownbits-add.mir
@@ -0,0 +1,234 @@
+# NOTE: Assertions have been autogenerated by utils/update_givaluetracking_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple aarch64 -passes="print<gisel-value-tracking>" %s -o - 2>&1 | FileCheck %s
+
+---
+name: Cst
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @Cst
+ ; CHECK-NEXT: %0:_ KnownBits:00000010 SignBits:6
+ ; CHECK-NEXT: %1:_ KnownBits:00011000 SignBits:3
+ ; CHECK-NEXT: %2:_ KnownBits:00011010 SignBits:3
+ %0:_(s8) = G_CONSTANT i8 2
+ %1:_(s8) = G_CONSTANT i8 24
+ %2:_(s8) = G_ADD %0, %1
+...
+---
+name: CstZero
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @CstZero
+ ; CHECK-NEXT: %0:_ KnownBits:00000001 SignBits:7
+ ; CHECK-NEXT: %1:_ KnownBits:11111111 SignBits:8
+ ; CHECK-NEXT: %2:_ KnownBits:00000000 SignBits:8
+ %0:_(s8) = G_CONSTANT i8 1
+ %1:_(s8) = G_CONSTANT i8 255
+ %2:_(s8) = G_ADD %0, %1
+...
+---
+name: CstNegOne
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @CstNegOne
+ ; CHECK-NEXT: %0:_ KnownBits:00000000 SignBits:8
+ ; CHECK-NEXT: %1:_ KnownBits:11111111 SignBits:8
+ ; CHECK-NEXT: %2:_ KnownBits:11111111 SignBits:8
+ %0:_(s8) = G_CONSTANT i8 0
+ %1:_(s8) = G_CONSTANT i8 255
+ %2:_(s8) = G_ADD %0, %1
+...
+---
+name: CstNeg
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @CstNeg
+ ; CHECK-NEXT: %0:_ KnownBits:11100000 SignBits:3
+ ; CHECK-NEXT: %1:_ KnownBits:00000010 SignBits:6
+ ; CHECK-NEXT: %2:_ KnownBits:11100010 SignBits:3
+ %0:_(s8) = G_CONSTANT i8 224
+ %1:_(s8) = G_CONSTANT i8 2
+ %2:_(s8) = G_ADD %0, %1
+...
+---
+name: ScalarVar
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @ScalarVar
+ ; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:???????? SignBits:1
+ ; CHECK-NEXT: %2:_ KnownBits:???????? SignBits:1
+ %0:_(s8) = COPY $b0
+ %1:_(s8) = COPY $b1
+ %2:_(s8) = G_ADD %0, %1
+...
+---
+name: ScalarRhsEarlyOut
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @ScalarRhsEarlyOut
+ ; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:00000011 SignBits:6
+ ; CHECK-NEXT: %2:_ KnownBits:???????? SignBits:1
+ %0:_(s8) = COPY $b0
+ %1:_(s8) = G_CONSTANT i8 3
+ %2:_(s8) = G_ADD %0, %1
+...
+---
+name: ScalarNonNegative
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @ScalarNonNegative
+ ; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:00001111 SignBits:4
+ ; CHECK-NEXT: %2:_ KnownBits:0000???? SignBits:4
+ ; CHECK-NEXT: %3:_ KnownBits:11111111 SignBits:8
+ ; CHECK-NEXT: %4:_ KnownBits:???????? SignBits:4
+ %0:_(s8) = COPY $b0
+ %1:_(s8) = G_CONSTANT i8 15
+ %2:_(s8) = G_AND %0, %1
+ %3:_(s8) = G_CONSTANT i8 255
+ %4:_(s8) = G_ADD %2, %3
+...
+---
+name: ScalarLhsEarlyOut
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @ScalarLhsEarlyOut
+ ; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:00000011 SignBits:6
+ ; CHECK-NEXT: %2:_ KnownBits:???????? SignBits:1
+ %0:_(s8) = COPY $b0
+ %1:_(s8) = G_CONSTANT i8 3
+ %2:_(s8) = G_ADD %1, %0
+...
+---
+name: ScalarPartKnown
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @ScalarPartKnown
+ ; CHECK-NEXT: %0:_ KnownBits:???????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:00001111 SignBits:4
+ ; CHECK-NEXT: %2:_ KnownBits:0000???? SignBits:4
+ ; CHECK-NEXT: %3:_ KnownBits:00000101 SignBits:5
+ ; CHECK-NEXT: %4:_ KnownBits:000????? SignBits:3
+ %0:_(s8) = COPY $b0
+ %1:_(s8) = G_CONSTANT i8 15
+ %2:_(s8) = G_AND %0, %1
+ %3:_(s8) = G_CONSTANT i8 5
+ %4:_(s8) = G_ADD %2, %3
+...
+---
+name: VectorVar
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorVar
+ ; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %2:_ KnownBits:???????????????? SignBits:1
+ %0:_(<4 x s16>) = COPY $d0
+ %1:_(<4 x s16>) = COPY $d1
+ %2:_(<4 x s16>) = G_ADD %0, %1
+...
+---
+name: VectorRhsEarlyOut
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorRhsEarlyOut
+ ; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:0000000000000011 SignBits:14
+ ; CHECK-NEXT: %2:_ KnownBits:0000000000000011 SignBits:14
+ ; CHECK-NEXT: %3:_ KnownBits:???????????????? SignBits:1
+ %0:_(<4 x s16>) = COPY $d0
+ %1:_(s16) = G_CONSTANT i16 3
+ %2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
+ %3:_(<4 x s16>) = G_ADD %2, %0
+...
+---
+name: VectorNonNegative
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorNonNegative
+ ; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:0000000011111111 SignBits:8
+ ; CHECK-NEXT: %2:_ KnownBits:0000000011111111 SignBits:8
+ ; CHECK-NEXT: %3:_ KnownBits:00000000???????? SignBits:8
+ ; CHECK-NEXT: %4:_ KnownBits:1111111111111111 SignBits:16
+ ; CHECK-NEXT: %5:_ KnownBits:1111111111111111 SignBits:16
+ ; CHECK-NEXT: %6:_ KnownBits:???????????????? SignBits:8
+ %0:_(<4 x s16>) = COPY $d0
+ %1:_(s16) = G_CONSTANT i16 255
+ %2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
+ %3:_(<4 x s16>) = G_AND %0, %2
+ %4:_(s16) = G_CONSTANT i16 65535
+ %5:_(<4 x s16>) = G_BUILD_VECTOR %4, %4, %4, %4
+ %6:_(<4 x s16>) = G_ADD %3, %5
+...
+---
+name: VectorLhsEarlyOut
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorLhsEarlyOut
+ ; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:0000000000000011 SignBits:14
+ ; CHECK-NEXT: %2:_ KnownBits:0000000000000011 SignBits:14
+ ; CHECK-NEXT: %3:_ KnownBits:???????????????? SignBits:1
+ %0:_(<4 x s16>) = COPY $d0
+ %1:_(s16) = G_CONSTANT i16 3
+ %2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
+ %3:_(<4 x s16>) = G_ADD %0, %2
+...
+---
+name: VectorPartKnown
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorPartKnown
+ ; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:0000000011111111 SignBits:8
+ ; CHECK-NEXT: %2:_ KnownBits:0000000011111111 SignBits:8
+ ; CHECK-NEXT: %3:_ KnownBits:00000000???????? SignBits:8
+ ; CHECK-NEXT: %4:_ KnownBits:0000000000101010 SignBits:10
+ ; CHECK-NEXT: %5:_ KnownBits:0000000001001010 SignBits:9
+ ; CHECK-NEXT: %6:_ KnownBits:000000000??01010 SignBits:9
+ ; CHECK-NEXT: %7:_ KnownBits:0000000????????? SignBits:7
+ %0:_(<4 x s16>) = COPY $d0
+ %1:_(s16) = G_CONSTANT i16 255
+ %2:_(<4 x s16>) = G_BUILD_VECTOR %1, %1, %1, %1
+ %3:_(<4 x s16>) = G_AND %0, %2
+ %4:_(s16) = G_CONSTANT i16 42
+ %5:_(s16) = G_CONSTANT i16 74
+ %6:_(<4 x s16>) = G_BUILD_VECTOR %4, %5, %5, %4
+ %7:_(<4 x s16>) = G_ADD %6, %3
+...
+---
+name: VectorCst36
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorCst36
+ ; CHECK-NEXT: %0:_ KnownBits:0000000000000011 SignBits:14
+ ; CHECK-NEXT: %1:_ KnownBits:0000000000000110 SignBits:13
+ ; CHECK-NEXT: %2:_ KnownBits:0000000000000?1? SignBits:13
+ ; CHECK-NEXT: %3:_ KnownBits:0000000000000?1? SignBits:13
+ ; CHECK-NEXT: %4:_ KnownBits:000000000000???? SignBits:12
+ %0:_(s16) = G_CONSTANT i16 3
+ %1:_(s16) = G_CONSTANT i16 6
+ %2:_(<4 x s16>) = G_BUILD_VECTOR %0, %1, %1, %0
+ %3:_(<4 x s16>) = G_BUILD_VECTOR %0, %1, %1, %0
+ %4:_(<4 x s16>) = G_ADD %2, %3
+...
+
+---
+name: VectorCst3unknown
+body: |
+ bb.1:
+ ; CHECK-LABEL: name: @VectorCst3unknown
+ ; CHECK-NEXT: %0:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %1:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %2:_ KnownBits:0000000000000011 SignBits:14
+ ; CHECK-NEXT: %3:_ KnownBits:???????????????? SignBits:1
+ ; CHECK-NEXT: %4:_ KnownBits:???????????????? SignBits:1
+ %0:_(<4 x s16>) = COPY $d0
+ %1:_(s16) = COPY $h0
+ %2:_(s16) = G_CONSTANT i16 3
+ %3:_(<4 x s16>) = G_BUILD_VECTOR %1, %2, %2, %1
+ %4:_(<4 x s16>) = G_ADD %0, %3
+...
diff --git a/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp b/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp
index c74d15782398a..1895992b4445c 100644
--- a/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp
+++ b/llvm/unittests/Target/AArch64/AArch64SelectionDAGTest.cpp
@@ -177,6 +177,100 @@ TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_VASHR) {
EXPECT_EQ(DAG->ComputeNumSignBits(Fr2), 5u);
}
+TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_ADD) {
+ SDLoc Loc;
+ auto IntVT = EVT::getIntegerVT(Context, 8);
+ auto Nneg1 = DAG->getConstant(0xFF, Loc, IntVT);
+ auto N0 = DAG->getConstant(0x00, Loc, IntVT);
+ auto N1 = DAG->getConstant(0x01, Loc, IntVT);
+ auto N5 = DAG->getConstant(0x05, Loc, IntVT);
+ auto Nsign1 = DAG->getConstant(0x55, Loc, IntVT);
+ auto UnknownOp = DAG->getRegister(0, IntVT);
+ auto Mask = DAG->getConstant(0x1e, Loc, IntVT);
+ auto Nsign3 = DAG->getNode(ISD::AND, Loc, IntVT, Mask, UnknownOp);
+ // RHS early out
+ // Nsign1 = 01010101
+ // Nsign3 = 000????0
+ auto OpRhsEo = DAG->getNode(ISD::ADD, Loc, IntVT, Nsign3, Nsign1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpRhsEo), 1u);
+
+ // ADD 0 -1
+ // N0 = 00000000
+ // Nneg1 = 11111111
+ auto OpNegZero = DAG->getNode(ISD::ADD, Loc, IntVT, N0, Nneg1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpNegZero), 8u);
+
+ // ADD 1 -1
+ // N1 = 00000001
+ // Nneg1 = 11111111
+ auto OpNegOne = DAG->getNode(ISD::ADD, Loc, IntVT, N1, Nneg1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpNegOne), 8u);
+
+ // Non negative
+ // Nsign3 = 000????0
+ // Nneg1 = 11111111
+ auto OpNonNeg = DAG->getNode(ISD::ADD, Loc, IntVT, Nsign3, Nneg1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpNonNeg), 3u);
+
+ // LHS early out
+ // Nsign1 = 01010101
+ // Nsign3 = 000????0
+ auto OpLhsEo = DAG->getNode(ISD::ADD, Loc, IntVT, Nsign1, Nsign3);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpLhsEo), 1u);
+
+ // Nsign3 = 000????0
+ // N5 = 00000101
+ auto Op = DAG->getNode(ISD::ADD, Loc, IntVT, Nsign3, N5);
+ EXPECT_EQ(DAG->ComputeNumSignBits(Op), 2u);
+}
+
+TEST_F(AArch64SelectionDAGTest, ComputeNumSignBits_ADDC) {
+ SDLoc Loc;
+ auto IntVT = EVT::getIntegerVT(Context, 8);
+ auto Nneg1 = DAG->getConstant(0xFF, Loc, IntVT);
+ auto N0 = DAG->getConstant(0x00, Loc, IntVT);
+ auto N1 = DAG->getConstant(0x01, Loc, IntVT);
+ auto N5 = DAG->getConstant(0x05, Loc, IntVT);
+ auto Nsign1 = DAG->getConstant(0x55, Loc, IntVT);
+ auto UnknownOp = DAG->getRegister(0, IntVT);
+ auto Mask = DAG->getConstant(0x1e, Loc, IntVT);
+ auto Nsign3 = DAG->getNode(ISD::AND, Loc, IntVT, Mask, UnknownOp);
+ // RHS early out
+ // Nsign1 = 01010101
+ // Nsign3 = 000????0
+ auto OpRhsEo = DAG->getNode(ISD::ADDC, Loc, IntVT, Nsign3, Nsign1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpRhsEo), 1u);
+
+ // ADD 0 -1
+ // N0 = 00000000
+ // Nneg1 = 11111111
+ auto OpNegZero = DAG->getNode(ISD::ADDC, Loc, IntVT, N0, Nneg1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpNegZero), 8u);
+
+ // ADD 1 -1
+ // N1 = 00000001
+ // Nneg1 = 11111111
+ auto OpNegOne = DAG->getNode(ISD::ADDC, Loc, IntVT, N1, Nneg1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpNegOne), 8u);
+
+ // Non negative
+ // Nsign3 = 000????0
+ // Nneg1 = 11111111
+ auto OpNonNeg = DAG->getNode(ISD::ADDC, Loc, IntVT, Nsign3, Nneg1);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpNonNeg), 3u);
+
+ // LHS early out
+ // Nsign1 = 01010101
+ // Nsign3 = 000????0
+ auto OpLhsEo = DAG->getNode(ISD::ADDC, Loc, IntVT, Nsign1, Nsign3);
+ EXPECT_EQ(DAG->ComputeNumSignBits(OpLhsEo), 1u);
+
+ // Nsign3 = 000????0
+ // N5 = 00000101
+ auto Op = DAG->getNode(ISD::ADDC, Loc, IntVT, Nsign3, N5);
+ EXPECT_EQ(DAG->ComputeNumSignBits(Op), 2u);
+}
+
TEST_F(AArch64SelectionDAGTest, SimplifyDemandedVectorElts_EXTRACT_SUBVECTOR) {
TargetLowering TL(*TM);
|
arsenm
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Gentle ping for review, thanks! :) |
arsenm
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Sep 25, 2025
| if (Known1.isNonNegative()) | ||
| return Src1NumSignBits; | ||
|
|
||
| // Otherwise, we treat this like an ADD. |
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In a follow up can add the carry out cases
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Will do!
What should we do about the carry out cases here? Is there an example I can follow?
I am asking because neither cases of ISD::ADD/ISD::ADDC in SelectionDAG::ComputeNumSignBits nor Global ISel Generic Opcode Doc mentions anything about the carry out cases. (Also David mentioned in issue #150515 that ADDC node is deprecated in GlobalISel. Does that mean ADD always carry in GlobalISel?)
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No, there are explicit uaddo_carry / saddo_carry. The DAG has the same, they just use explicit virtual register outputs instead of glue
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Ah thanks for the clarification!
Are you referring to this part that handles carry in SelectionDAG, but not implemented in GlobalISel?
RKSimon
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Sep 30, 2025
jayfoad
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jayfoad
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Oct 2, 2025
| Register Src2 = MI.getOperand(2).getReg(); | ||
| unsigned Src2NumSignBits = | ||
| computeNumSignBits(Src2, DemandedElts, Depth + 1); | ||
| if (Src2NumSignBits == 1) |
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Possible micro-optimization:
Suggested change
| if (Src2NumSignBits == 1) | |
| if (Src2NumSignBits <= 2) |
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Even better, sink this whole Src2NumSignBits calculation below the if (Known2.isAllOnes()) { ... } special case.
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When I initially submitted this change, I had this calculation below the if (Known2.isAllOnes()) { ... }, but Matt suggested that we "try RHS first` earlier, so now it looks like this.
@arsenm Matt did I misunderstood what you meant?
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Gentle ping for review, thanks! :) |
arsenm
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@ningxinr please can you resolve the conflicts? |
Co-authored-by: Matt Arsenault <arsenm2@gmail.com>
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Done! Thanks, Simon! |
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/31422 Here is the relevant piece of the build log for the reference |
This one looks like an irrelevant intermittent failure. It timed out, similar to another failure that happened a day ago: https://lab.llvm.org/buildbot/#/builders/129/builds/31372 |
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This patch ports the ISD::ADD handling from SelectionDAG’s ComputeNumSignBits to GlobalISel. Related to llvm#150515. --------- Co-authored-by: Matt Arsenault <arsenm2@gmail.com> Co-authored-by: Simon Pilgrim <llvm-dev@redking.me.uk>
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This patch ports the ISD::ADD handling from SelectionDAG’s ComputeNumSignBits to GlobalISel.
Related to #150515.