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[mlir][IntRangeInference] Handle ceildivsi(INT_MIN, x > 1) as expected (#116284)

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Fixes #115293

While the definition of ceildivsi is integer division, rounding up, most
implementations will use `-(-a / b)` for dividing `a ceildiv b` with `a`
negative and `b` positive.

Mathematically, and for most integers, these two definitions are
equivalent. However, with `a == INT_MIN`, the initial negation is a
noop, which means that, while divinding and rounding up would give a
negative result, `-((- INT_MIN) / b)` is `-(INT_MIN / b)`, which is
positive.

This commit adds a special case to ceilDivSI inference to handle this
case and bring it in line with the operational instead of the
mathematical semantics of ceiling division.
This commit is contained in:
Krzysztof Drewniak 2024-11-15 09:43:05 -08:00 committed by GitHub
parent d82422f69c
commit f2e42d9324
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2 changed files with 22 additions and 0 deletions
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9
mlir/lib/Interfaces/Utils/InferIntRangeCommon.cpp
View File

@ -375,6 +375,15 @@ mlir::intrange::inferCeilDivS(ArrayRef<ConstantIntRanges> argRanges) {
result.sadd_ov(APInt(result.getBitWidth(), 1), overflowed);
return overflowed ? std::optional<APInt>() : corrected;
}
// Special case where the usual implementation of ceilDiv causes
// INT_MIN / [positive number] to be positive. This doesn't match the
// definition of signed ceiling division mathematically, but it prevents
// inconsistent constant-folding results. This arises because (-int_min) is
// still negative, so -(-int_min / b) is -(int_min / b), which is
// positive See #115293.
if (lhs.isMinSignedValue() && rhs.sgt(1)) {
return -result;
}
return result;
};
return inferDivSRange(lhs, rhs, ceilDivSIFix);

13
mlir/test/Dialect/Arith/int-range-interface.mlir
View File

@ -249,6 +249,19 @@ func.func @ceil_divsi(%arg0 : index) -> i1 {
func.return %10 : i1
}
// CHECK-LABEL: func @ceil_divsi_intmin_bug_115293
// CHECK: %[[ret:.*]] = arith.constant true
// CHECK: return %[[ret]]
func.func @ceil_divsi_intmin_bug_115293() -> i1 {
%intMin_i64 = test.with_bounds { smin = -9223372036854775808 : si64, smax = -9223372036854775808 : si64, umin = 9223372036854775808 : ui64, umax = 9223372036854775808 : ui64 } : i64
%denom_i64 = test.with_bounds { smin = 1189465982 : si64, smax = 1189465982 : si64, umin = 1189465982 : ui64, umax = 1189465982 : ui64 } : i64
%res_i64 = test.with_bounds { smin = 7754212542 : si64, smax = 7754212542 : si64, umin = 7754212542 : ui64, umax = 7754212542 : ui64 } : i64
%0 = arith.ceildivsi %intMin_i64, %denom_i64 : i64
%1 = arith.cmpi eq, %0, %res_i64 : i64
func.return %1 : i1
}
// CHECK-LABEL: func @floor_divsi
// CHECK: %[[true:.*]] = arith.constant true
// CHECK: return %[[true]]