Eagerly constant fold all arithmetic - #771
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dsharlet wants to merge 9 commits into
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vksnk
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Feb 9, 2026
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| SLINKY_NO_INLINE void test_expr(expr pattern, expr replacement, const std::string& rule_str) { | ||
| SLINKY_NO_INLINE void test_expr(expr pattern, expr replacement, const std::string& rule_str, bool& applied) { | ||
| expr simplified = simplify(pattern); |
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I think there should be applied = false; in the beginning, so it doesn't have to rely on what was passed (and I think it's incorrect to keep it unchanged).
| ASSERT_THAT(constant_upper_bound(min(x, 4)), matches(4)); | ||
| ASSERT_THAT(constant_upper_bound(max(x, 4)), matches(max(x, 4))); | ||
| ASSERT_THAT(constant_upper_bound(!min(x, 0)), matches(1)); | ||
| ASSERT_THAT(constant_upper_bound(!min(x, -1)), matches(1)); // TODO: We might be able to prove this is 0 |
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re TODO: Shouldn't this always be 1?
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This changes the construction of expressions to eagerly constant fold arithmetic as we encounter it.
When client code is constructing expressions, they might check if an expression is a constant, but that expression might be constant arithmetic that produces that constant instead. This is an annoying thing to deal with and leads to bugs.
The main downside of this change is that it doesn't maintain expressions as the user expected. This is both surprising in a different way, and this also did affect our tests a lot.
I had hoped this would make the simplifier faster, but it's actually slower. I guess this makes sense, the constant folding logic in the simplifier was cheap, but now we do that logic when constructing all expressions.
The change also uncovered quite a few bugs:
min(a, b) < cand similar cases.!xwas wrongSome of these bugs are pretty surprising, they are not subtle edge cases.