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[Comb] Fix excessive const shifts causing crashes and invalid IR #8696

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Merged
fabianschuiki merged 1 commit into from
Jul 12, 2025
Merged

[Comb] Fix excessive const shifts causing crashes and invalid IR #8696

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27 changes: 15 additions & 12 deletions lib/Dialect/Comb/CombFolds.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -307,14 +307,13 @@ static Attribute constFoldBinaryOp(ArrayRef<Attribute> operands,

OpFoldResult ShlOp::fold(FoldAdaptor adaptor) {
if (auto rhs = dyn_cast_or_null<IntegerAttr>(adaptor.getRhs())) {
unsigned shift = rhs.getValue().getZExtValue();
unsigned width = getType().getIntOrFloatBitWidth();
if (shift == 0)
if (rhs.getValue().isZero())
return getOperand(0);
if (width <= shift)

unsigned width = getType().getIntOrFloatBitWidth();
if (rhs.getValue().uge(width))
return getIntAttr(APInt::getZero(width), getContext());
}

return constFoldBinaryOp(adaptor.getOperands(), hw::PEO::Shl);
}

Expand All @@ -325,6 +324,8 @@ LogicalResult ShlOp::canonicalize(ShlOp op, PatternRewriter &rewriter) {
return failure();

unsigned width = cast<IntegerType>(op.getLhs().getType()).getWidth();
if (value.ugt(width))
value = width;
unsigned shift = value.getZExtValue();

// This case is handled by fold.
Expand All @@ -344,12 +345,11 @@ LogicalResult ShlOp::canonicalize(ShlOp op, PatternRewriter &rewriter) {

OpFoldResult ShrUOp::fold(FoldAdaptor adaptor) {
if (auto rhs = dyn_cast_or_null<IntegerAttr>(adaptor.getRhs())) {
unsigned shift = rhs.getValue().getZExtValue();
if (shift == 0)
if (rhs.getValue().isZero())
return getOperand(0);

unsigned width = getType().getIntOrFloatBitWidth();
if (width <= shift)
if (rhs.getValue().uge(width))
return getIntAttr(APInt::getZero(width), getContext());
}
return constFoldBinaryOp(adaptor.getOperands(), hw::PEO::ShrU);
Expand All @@ -362,6 +362,8 @@ LogicalResult ShrUOp::canonicalize(ShrUOp op, PatternRewriter &rewriter) {
return failure();

unsigned width = cast<IntegerType>(op.getLhs().getType()).getWidth();
if (value.ugt(width))
value = width;
unsigned shift = value.getZExtValue();

// This case is handled by fold.
Expand All @@ -380,10 +382,9 @@ LogicalResult ShrUOp::canonicalize(ShrUOp op, PatternRewriter &rewriter) {
}

OpFoldResult ShrSOp::fold(FoldAdaptor adaptor) {
if (auto rhs = dyn_cast_or_null<IntegerAttr>(adaptor.getRhs())) {
if (rhs.getValue().getZExtValue() == 0)
if (auto rhs = dyn_cast_or_null<IntegerAttr>(adaptor.getRhs()))
if (rhs.getValue().isZero())
return getOperand(0);
}
return constFoldBinaryOp(adaptor.getOperands(), hw::PEO::ShrS);
}

Expand All @@ -394,13 +395,15 @@ LogicalResult ShrSOp::canonicalize(ShrSOp op, PatternRewriter &rewriter) {
return failure();

unsigned width = cast<IntegerType>(op.getLhs().getType()).getWidth();
if (value.ugt(width))
value = width;
unsigned shift = value.getZExtValue();

auto topbit =
rewriter.createOrFold<ExtractOp>(op.getLoc(), op.getLhs(), width - 1, 1);
auto sext = rewriter.createOrFold<ReplicateOp>(op.getLoc(), topbit, shift);

if (width <= shift) {
if (width == shift) {
replaceOpAndCopyNamehint(rewriter, op, {sext});
return success();
}
Expand Down
87 changes: 87 additions & 0 deletions test/Dialect/Comb/canonicalization.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -1714,3 +1714,90 @@ func.func @dontAssumeMuxCondIfOperandIsOtherwiseObservable(%arg0: i1, %arg1: i1)
%2 = comb.mux %arg0, %0, %1 : i1
return %2 : i1
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShlTotalShiftOut
hw.module @ShlTotalShiftOut(in %a: i4, out y: i4) {
// CHECK: [[TMP1:%.+]] = hw.constant 0
// CHECK: hw.output [[TMP1]]
%0 = hw.constant 7 : i4
%1 = comb.shl %a, %0 : i4
hw.output %1 : i4
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShrUTotalShiftOut
hw.module @ShrUTotalShiftOut(in %a: i4, out y: i4) {
// CHECK: [[TMP1:%.+]] = hw.constant 0
// CHECK: hw.output [[TMP1]]
%0 = hw.constant 7 : i4
%1 = comb.shru %a, %0 : i4
hw.output %1 : i4
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShrSTotalShiftOut
hw.module @ShrSTotalShiftOut(in %a: i4, out y: i4) {
// CHECK: [[TMP1:%.+]] = comb.extract %a from 3
// CHECK: [[TMP2:%.+]] = comb.replicate [[TMP1]] : (i1) -> i4
%0 = hw.constant 7 : i4
%1 = comb.shrs %a, %0 : i4
hw.output %1 : i4
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShlExcessiveShiftConst
hw.module @ShlExcessiveShiftConst(in %a: i1000, out y: i1000) {
// CHECK: [[TMP1:%.+]] = hw.constant 0
// CHECK: hw.output [[TMP1]]
%0 = hw.constant -1 : i1000
%1 = comb.shl %a, %0 : i1000
hw.output %1 : i1000
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShrUExcessiveShiftConst
hw.module @ShrUExcessiveShiftConst(in %a: i1000, out y: i1000) {
// CHECK: [[TMP1:%.+]] = hw.constant 0
// CHECK: hw.output [[TMP1]]
%0 = hw.constant -1 : i1000
%1 = comb.shru %a, %0 : i1000
hw.output %1 : i1000
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShrSExcessiveShiftConst
hw.module @ShrSExcessiveShiftConst(in %a: i1000, out y: i1000) {
// CHECK: [[TMP1:%.+]] = comb.extract %a from 999
// CHECK: [[TMP2:%.+]] = comb.replicate [[TMP1]] : (i1) -> i1000
%0 = hw.constant -1 : i1000
%1 = comb.shrs %a, %0 : i1000
hw.output %1 : i1000
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShlWideZeroShift
hw.module @ShlWideZeroShift(in %a: i1000, out y: i1000) {
// CHECK: hw.output %a
%0 = hw.constant 0 : i1000
%1 = comb.shl %a, %0 : i1000
hw.output %1 : i1000
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShrUWideZeroShift
hw.module @ShrUWideZeroShift(in %a: i1000, out y: i1000) {
// CHECK: hw.output %a
%0 = hw.constant 0 : i1000
%1 = comb.shru %a, %0 : i1000
hw.output %1 : i1000
}

// See https://github.com/llvm/circt/issues/8695
// CHECK-LABEL: @ShrSWideZeroShift
hw.module @ShrSWideZeroShift(in %a: i1000, out y: i1000) {
// CHECK: hw.output %a
%0 = hw.constant 0 : i1000
%1 = comb.shrs %a, %0 : i1000
hw.output %1 : i1000
}