[Bug middle-end/105984] New: [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[Bug middle-end/105984] New: [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105984

            Bug ID: 105984
           Summary: [13 Regression] wrong code with
                    __builtin_mul_overflow_p() at -O1
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 53139
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53139&action=edit
reduced testcase

Output:
$ x86_64-pc-linux-gnu-gcc -O1 testcase.c
$ ./a.out 
Aborted

The generated code:
main:
        mov     rax, QWORD PTR g[rip]
        sub     rax, 1
        mov     QWORD PTR g[rip], rax
        jne     .L6
        mov     eax, 0
        ret

just shows the multiplication was evaluated to overflow at compile time.

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r13-1092-20220614173648-g3e16b4359e8-checking-yes-rtl-df-extra-nobootstrap-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/13.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--disable-bootstrap --with-cloog --with-ppl --with-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r13-1092-20220614173648-g3e16b4359e8-checking-yes-rtl-df-extra-nobootstrap-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.0.0 20220614 (experimental) (GCC)

[Bug middle-end/105984] [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105984

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection
   Target Milestone|---                         |13.0

[Bug middle-end/105984] [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105984

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-06-15
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
           Keywords|needs-bisection             |
           Priority|P3                          |P1
     Ever confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with my r13-979-g1982fe2692b6c3b7f969ffc4edac59f9d4359e91

[Bug middle-end/105984] [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105984

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 53143
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53143&action=edit
gcc13-pr105984.patch

Untested fix.

[Bug middle-end/105984] [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105984

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:74e6a40335765077e235269f19d2d9905d0d9e44

commit r13-1133-g74e6a40335765077e235269f19d2d9905d0d9e44
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jun 16 14:36:04 2022 +0200

    match.pd: Fix up __builtin_mul_overflow_p signed type optimization
[PR105984]

    Earlier in the simplification pattern, we require that @0 has compatible
    type to the type of IMAGPART_EXPR, but for @1 which is a non-zero constant
    all we require is that it the constant fits into that type.
    Later the code checks if the constant is negative, because when min / max
    values are divided by negative divisor, lo will be higher than hi.
    In the following testcase, @1 has unsigned char type, while @0 has
    int type, so @1 which is 254 is wi::neg_p and we were swapping lo and hi,
    even when @1 cast to int isn't negative.

    We could use tree_int_cst_sgn (@1) < 0 as the check instead and it would
    work both for narrower types of @1 and even same or wider ones, but
    I've noticed we probably don't want to call fold_convert (TREE_TYPE (@0),
@1)
    twice and when we save that result in a temporary, we can just use
wi::neg_p
    on that temporary.

    2022-06-16  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/105984
            * match.pd (__builtin_mul_overflow_p (x, cst, (stype) 0) ->
            x > stype_max / cst || x < stype_min / cst): fold_convert @1
            to TREE_TYPE (@0) just once and test for negative divisor
            also on that folded constant instead of on @1.

            * gcc.c-torture/execute/pr105984.c: New test.

[Bug middle-end/105984] [13 Regression] wrong code with __builtin_mul_overflow_p() at -O1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105984

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed, thanks for the report.