[Bug tree-optimization/84811] [8 Regression] ICE on valid code at -O3 in 64-bit mode on x86_64-linux-gnu: in smallest_mode_for_size, at stor-layout.c:355

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84811

--- Comment #26 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Author: rsandifo
Date: Wed Mar 21 20:52:15 2018
New Revision: 258743

URL: https://gcc.gnu.org/viewcvs?rev=258743&root=gcc&view=rev
Log:
poly_span_traits fixes (PR 84811)

This patch fixes incorrect results for HOST_WIDE_INT positions
at opposite extremes when used with HOST_WIDE_INT sizes.  It also
fixes UB when comparing such positions with unsigned HOST_WIDE_INT
sizes (although the results in that case were wrapv-correct).

2018-03-20  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
        PR tree-optimization/84811
        * poly-int.h (poly_span_traits): Remove the T3 parameter and
        promote HOST_WIDE_INT T2 - T1 results to unsigned HOST_WIDE_INT.
        (maybe_in_range_p, known_in_range_p, ranges_known_overlap_p):
        (known_subrange_p): Update accordingly.  Cast each value involved
        in the size comparison, rather than casting the result of the
        subtraction.

gcc/testsuite/
        PR tree-optimization/84811
        * gcc.dg/torture/pr84811.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr84811.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/poly-int.h
    trunk/gcc/testsuite/ChangeLog