https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97960
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[8/9/10/11 Regression] |[8/9/10 Regression] Wrong
|Wrong code at -O3 since |code at -O3 since
|r8-6511-g3ae129323d |r8-6511-g3ae129323d
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk by
https://gcc.gnu.org/g:4cf70c20cb10acd6fb1016611d05540728176b60
commit r11-5904-g4cf70c20cb10acd6fb1016611d05540728176b60
Author: Richard Sandiford <[email protected]>
Date: Thu Dec 10 12:10:00 2020 +0000
data-ref: Rework integer handling in split_constant_offset [PR98069]
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.
