On Tue, Mar 17, 2020 at 9:35 AM Jakub Jelinek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi!
>
> The following testcase FAILs with -O2 -fcompare-debug, but the reason isn't
> that we'd emit different code based on -g or non-debug, but rather that
> we emit different code depending on whether -w is used or not (or e.g.
> -Wno-stringop-overflow or whether some other pass emitted some other warning
> already on the call).
>
> Code generation shouldn't depend on whether we emit a warning or not if at
> all possible.
>
> The following patch punts (i.e. doesn't optimize the strnlen call to a
> constant value) if we would emit the warning if it was enabled.
> In the PR there is an alternate patch which does optimize the strnlen call
> no matter if we emit the warning or not, though I think I prefer the version
> below, e.g. the strnlen call might be crossing field boundaries, which is in
> strict reading undefined, but I'd be afraid people do that in the real
> world programs.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
> 2020-03-17 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/94189
> * builtins.c (expand_builtin_strnlen): Do return NULL_RTX if we would
> emit a warning if it was enabled and don't depend on TREE_NO_WARNING
> for code-generation.
>
> * gcc.dg/pr94189.c: New test.
>
> --- gcc/builtins.c.jj 2020-01-12 11:54:36.198416652 +0100
> +++ gcc/builtins.c 2020-03-16 11:39:02.400537378 +0100
> @@ -3142,27 +3142,25 @@ expand_builtin_strnlen (tree exp, rtx ta
> return NULL_RTX;
> }
>
> - if (lendata.decl
> - && !TREE_NO_WARNING (exp)
> - && ((tree_int_cst_lt (len, bound))
> - || !exact))
> + if (lendata.decl && (tree_int_cst_lt (len, bound) || !exact))
> {
> location_t warnloc
> = expansion_point_location_if_in_system_header (loc);
>
> - if (warning_at (warnloc, OPT_Wstringop_overflow_,
> - exact
> - ? G_("%K%qD specified bound %E exceeds the size %E "
> - "of unterminated array")
> - : G_("%K%qD specified bound %E may exceed the size "
> - "of at most %E of unterminated array"),
> - exp, func, bound, len))
> + if (!TREE_NO_WARNING (exp)
> + && warning_at (warnloc, OPT_Wstringop_overflow_,
> + exact
> + ? G_("%K%qD specified bound %E exceeds the size "
> + "%E of unterminated array")
> + : G_("%K%qD specified bound %E may exceed the "
> + "size of at most %E of unterminated array"),
> + exp, func, bound, len))
> {
> inform (DECL_SOURCE_LOCATION (lendata.decl),
> "referenced argument declared here");
> TREE_NO_WARNING (exp) = true;
> - return NULL_RTX;
> }
> + return NULL_RTX;
> }
>
> if (!len)
> --- gcc/testsuite/gcc.dg/pr94189.c.jj 2020-03-16 11:32:17.785541399 +0100
> +++ gcc/testsuite/gcc.dg/pr94189.c 2020-03-16 11:31:43.257053763 +0100
> @@ -0,0 +1,11 @@
> +/* PR middle-end/94189 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fcompare-debug" } */
> +
> +const char a[] = { 'a', 'b', 'c', 'd' };/* { dg-message "declared here" } */
> +
> +int
> +foo (void)
> +{
> + return __builtin_strnlen (a, 5); /* { dg-warning "specified bound 5
> exceeds the size 4 of unterminated array" } */
> +}
>
> Jakub
>
