Lunderberg commented on code in PR #13724:
URL: https://github.com/apache/tvm/pull/13724#discussion_r1065866668
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src/tir/transforms/lower_intrin.cc:
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@@ -165,21 +179,34 @@ class IntrinInjecter : public
tvm::arith::IRMutatorWithAnalyzer {
// Common pass, positive divisor
if (analyzer_->CanProveGreaterEqual(op->a, 0)) {
return truncmod(op->a, op->b);
+ }
+
+ // If the numerator's lower bound is known, express the floormod
+ // in terms of truncmod using only positive operands.
+ arith::ConstIntBound const_int_bound = analyzer_->const_int_bound(op->a);
+ if (const_int_bound->min_value != arith::ConstIntBound::kNegInf &&
+ const_int_bound->min_value < 0 &&
+ const_int_bound->min_value > -(1LL << (op->a->dtype.bits() - 1))) {
+ IntImm min(op->a->dtype, const_int_bound->min_value);
+ PrimExpr ceildiv = truncdiv(-min + (op->b - 1), op->b);
+ PrimExpr offset_numerator = analyzer_->Simplify(op->a + op->b *
ceildiv);
+ return truncmod(offset_numerator, op->b);
Review Comment:
Yup, that derivation is correct, and I've added a comment here as well.
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