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PR98069 is about a case in which split_constant_offset miscategorises an expression of the form: int foo; … POINTER_PLUS_EXPR<base, (sizetype)(INT_MIN - foo) * size> as: base: base offset: (sizetype) (-foo) * size init: INT_MIN * size “-foo” overflows when “foo” is INT_MIN, whereas the original expression didn't overflow in that case. As discussed in the PR trail, we could simply ignore the fact that int overflow is undefined and treat it as a wrapping type, but that is likely to pessimise quite a few cases. This patch instead reworks split_constant_offset so that: - it treats integer operations as having an implicit cast to sizetype - for integer operations, the returned VAR has type sizetype In other words, the problem becomes to express: (sizetype) (OP0 CODE OP1) as: VAR:sizetype + (sizetype) OFF:ssizetype The top-level integer split_constant_offset will (usually) be a sizetype POINTER_PLUS operand, so the extra cast to sizetype disappears. But adding the cast allows the conversion handling to defer a lot of the difficult cases to the recursive split_constant_offset call, which can detect overflow on individual operations. The net effect is to analyse the access above as: base: base offset: -(sizetype) foo * size init: INT_MIN * size See the comments in the patch for more details. gcc/ PR tree-optimization/98069 * tree-data-ref.c (compute_distributive_range): New function. (nop_conversion_for_offset_p): Likewise. (split_constant_offset): In the internal overload, treat integer expressions as having an implicit cast to sizetype and express them accordingly. Pass back the range of the original (uncast) expression in a new range parameter. (split_constant_offset_1): Likewise. Rework the handling of conversions to account for the implicit sizetype casts.
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