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[mlir][intrange] Fix arith.shl inference in case of overflow #91737

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May 13, 2024
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[mlir][intrange] Fix arith.shl inference in case of overflow #91737

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[mlir][intrange] Fix `arith.shl` inference in case of overflow
ubfx May 10, 2024
bf81f62
Address review
ubfx May 10, 2024
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19 changes: 17 additions & 2 deletions mlir/lib/Interfaces/Utils/InferIntRangeCommon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -544,15 +544,30 @@ mlir::intrange::inferXor(ArrayRef<ConstantIntRanges> argRanges) {
ConstantIntRanges
mlir::intrange::inferShl(ArrayRef<ConstantIntRanges> argRanges) {
const ConstantIntRanges &lhs = argRanges[0], &rhs = argRanges[1];
const APInt &lhsSMin = lhs.smin(), &lhsSMax = lhs.smax(),
&lhsUMax = lhs.umax(), &rhsUMin = rhs.umin(),
&rhsUMax = rhs.umax();

ConstArithFn shl = [](const APInt &l,
const APInt &r) -> std::optional<APInt> {
return r.uge(r.getBitWidth()) ? std::optional<APInt>() : l.shl(r);
};

// The minMax inference does not work when there is danger of overflow. In the
// signed case, this leads to the obvious problem that the sign bit might
// change. In the unsigned case, it also leads to problems because the largest
// LHS shifted by the largest RHS does not necessarily result in the largest
// result anymore.
assert(rhsUMax.isNonNegative() && "Unexpected negative shift count");
if (rhsUMax.uge(lhsSMin.getNumSignBits()) ||
rhsUMax.uge(lhsSMax.getNumSignBits()))
return ConstantIntRanges::maxRange(lhsUMax.getBitWidth());

ConstantIntRanges urange =
minMaxBy(shl, {lhs.umin(), lhs.umax()}, {rhs.umin(), rhs.umax()},
minMaxBy(shl, {lhs.umin(), lhsUMax}, {rhsUMin, rhsUMax},
/*isSigned=*/false);
ConstantIntRanges srange =
minMaxBy(shl, {lhs.smin(), lhs.smax()}, {rhs.umin(), rhs.umax()},
minMaxBy(shl, {lhsSMin, lhsSMax}, {rhsUMin, rhsUMax},
/*isSigned=*/true);
return urange.intersection(srange);
}
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29 changes: 29 additions & 0 deletions mlir/test/Dialect/Arith/int-range-opts.mlir
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Expand Up @@ -71,3 +71,32 @@ func.func @test() -> i1 {
%1 = arith.cmpi sle, %0, %cst1 : index
return %1: i1
}

// -----

// CHECK-LABEL: func @test
// CHECK: test.reflect_bounds {smax = 24 : index, smin = 0 : index, umax = 24 : index, umin = 0 : index}
func.func @test() -> index {
%cst1 = arith.constant 1 : i8
%0 = test.with_bounds { umin = 0 : index, umax = 12 : index, smin = 0 : index, smax = 12 : index }
%i8val = arith.index_cast %0 : index to i8
%shifted = arith.shli %i8val, %cst1 : i8
%si = arith.index_cast %shifted : i8 to index
%1 = test.reflect_bounds %si
return %1: index
}

// -----

// CHECK-LABEL: func @test
// CHECK: test.reflect_bounds {smax = 127 : index, smin = -128 : index, umax = -1 : index, umin = 0 : index}
func.func @test() -> index {
%cst1 = arith.constant 1 : i8
%0 = test.with_bounds { umin = 0 : index, umax = 127 : index, smin = 0 : index, smax = 127 : index }
%i8val = arith.index_cast %0 : index to i8
%shifted = arith.shli %i8val, %cst1 : i8
%si = arith.index_cast %shifted : i8 to index
%1 = test.reflect_bounds %si
return %1: index
}

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