vinx13 commented on code in PR #11373:
URL: https://github.com/apache/tvm/pull/11373#discussion_r879870628
##########
src/arith/rewrite_simplify.cc:
##########
@@ -256,13 +256,16 @@ PrimExpr RewriteSimplifier::Impl::VisitExpr_(const
SubNode* op) {
TVM_TRY_REWRITE(broadcast(x, lanes) - broadcast(y, lanes), broadcast(x -
y, lanes));
}
+ // cancelation rules
+ TVM_TRY_REWRITE_IF(x - x, ZeroWithTypeLike(x),
+ SideEffect(x.Eval()) <= CallEffectKind::kReadState);
+ TVM_TRY_REWRITE_IF((x + y) - y, x, SideEffect(y.Eval()) <=
CallEffectKind::kReadState);
+ TVM_TRY_REWRITE_IF((x + y) - x, y, SideEffect(x.Eval()) <=
CallEffectKind::kReadState);
+ TVM_TRY_REWRITE_IF(x - (y + x), 0 - y, SideEffect(x.Eval()) <=
CallEffectKind::kReadState);
+ TVM_TRY_REWRITE_IF(x - (x + y), 0 - y, SideEffect(x.Eval()) <=
CallEffectKind::kReadState);
+
if (IsIndexType(op->dtype)) {
// Index rules
- // cancelation rules
Review Comment:
The integer simplifcation should be fast path (and clean, hopefully without
Nans), it would be better to put new rules in else branch even if it means some
duplications, since (recursively) checking side effects is expensive.
Doing floating point simplification is probably fine, but given the
possibility of introducing additional types, it might be safer to say something
like
```
if (IsIndexType(op->dtype)) {
old rules
} else if (op->dtype.is_float())
new rules
}
```
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