[Bug tree-optimization/78327] -Walloca-large-than false positives due to bad range info for signed integers in [-TYPE_MAX + N, N]

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78327

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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           Keywords|                            |missed-optimization

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
Already in the original dump, we can see that the comparisons are optimized to
different shapes:

-  if ((signed char) ((unsigned char) n + 125) < 0)
+  if ((unsigned char) n + 125 > 126)

For the second one, VRP knows how to build an assert_expr and interpret the
consequences on n, while for the first one it doesn't. Since we turn nice
comparisons into the first shape, I guess we should teach VRP to recognize it.