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Ensure 0 <= x mod N < N semantics #484

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Mar 6, 2025
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Ensure 0 <= x mod N < N semantics #484

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26 changes: 19 additions & 7 deletions mlir/lib/Analysis/AffineExprBounds.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
//===----------------------------------------------------------------------===//
#include "mlir/Analysis/AffineExprBounds.h"

#include "mlir/IR/AffineExpr.h"
#include "mlir/IR/AffineExprVisitor.h"
#include "mlir/IR/AffineMap.h"
#include "mlir/IR/BuiltinAttributes.h"
Expand Down Expand Up @@ -158,13 +159,24 @@ AffineExprBoundsVisitor::visitFloorDivExpr(AffineBinaryOpExpr expr) {
return failure();
}
LogicalResult AffineExprBoundsVisitor::visitModExpr(AffineBinaryOpExpr expr) {
inferBinOpRange(
expr, [boundsSigned = boundsSigned](ArrayRef<ConstantIntRanges> ranges) {
if (boundsSigned) {
return intrange::inferRemS(ranges);
}
return intrange::inferRemU(ranges);
});
// Only support integers >= 1 as RHS.
auto rhsConst = dyn_cast<AffineConstantExpr>(expr.getRHS());
if (!rhsConst || rhsConst.getValue() < 1)
return failure();

inferBinOpRange(expr, [boundsSigned =
boundsSigned](ArrayRef<ConstantIntRanges> ranges) {
// Mod must return a value between 0 and N-1.
// Computing (N + (expr mod N)) mod N is guaranteed to yield a result in
// this range.
if (boundsSigned) {
auto rhs = ranges[1];
auto lhs = ranges[0];
return intrange::inferRemS(
{intrange::inferAdd({intrange::inferRemS({lhs, rhs}), rhs}), rhs});
}
return intrange::inferRemU(ranges);
});
return success();
}
LogicalResult AffineExprBoundsVisitor::visitDimExpr(AffineDimExpr expr) {
Expand Down
10 changes: 10 additions & 0 deletions mlir/test/Analysis/test-affine-expr-bounds.mlir
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,16 @@ func.func @test_compute_affine_expr_bounds() {
// CHECK-SAME: expr_ub = 3
"test.mod_not_wrapping_around"() {affine_map = affine_map<(d0) -> (((d0 + 12) mod 11) mod 5)>, lbs = [0], ubs = [2]} : () -> ()

// CHECK: "test.mod_neg"()
// CHECK-SAME: expr_lb = 1
// CHECK-SAME: expr_ub = 3
"test.mod_neg"() {affine_map = affine_map<(d0) -> (d0 mod 5)>, lbs = [-4], ubs = [-2]} : () -> ()

// CHECK: "test.mod_wrapping_by_zero"()
// CHECK-SAME: expr_lb = 0
// CHECK-SAME: expr_ub = 4
"test.mod_wrapping_by_zero"() {affine_map = affine_map<(d0) -> (d0 mod 5)>, lbs = [-2], ubs = [1]} : () -> ()

// FloorDiv

// CHECK: "test.floordiv_basic"()
Expand Down
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