[Bug rtl-optimization/105744] New: [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[Bug rtl-optimization/105744] New: [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

            Bug ID: 105744
           Summary: [11/12/13 Regression] wrong code with
                    -fexpensive-optimizations -flive-range-shrinkage on
                    powerpc64le-unknown-linux-gnu
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: powerpc64le-unknown-linux-gnu

Created attachment 53040
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53040&action=edit
reduced testcase

Output:
$ powerpc64le-unknown-linux-gnu-gcc -fexpensive-optimizations
-flive-range-shrinkage testcase.c -static
$ qemu-ppc64le -- ./a.out 
qemu: uncaught target signal 6 (Aborted) - core dumped
Aborted

(gdb) p/x a
$5 = {0x0, 0x0, 0x0, 0x0}
(gdb) p/x b
$6 = {0x0, 0x0, 0x0, 0x0}
(gdb) p/x c
$7 = {0xffff00, 0x0, 0x0, 0x0}
(gdb) p/x d
$8 = {0x0, 0x0, 0x0, 0x0}
(gdb) p/x e
$9 = {0x0, 0x0, 0x0, 0x0}
(gdb) p/x u
$10 = {0x1 <repeats 32 times>}


$ powerpc64le-unknown-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-powerpc64le/bin/powerpc64le-unknown-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r13-771-20220526001630-g3dff965cae6-checking-yes-rtl-df-extra-powerpc64le/bin/../libexec/gcc/powerpc64le-unknown-linux-gnu/13.0.0/lto-wrapper
Target: powerpc64le-unknown-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--with-cloog --with-ppl --with-isl
--with-sysroot=/usr/powerpc64le-unknown-linux-gnu --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=powerpc64le-unknown-linux-gnu
--with-ld=/usr/bin/powerpc64le-unknown-linux-gnu-ld
--with-as=/usr/bin/powerpc64le-unknown-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r13-771-20220526001630-g3dff965cae6-checking-yes-rtl-df-extra-powerpc64le
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.0.0 20220526 (experimental) (GCC)

[Bug rtl-optimization/105744] [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.4

[Bug rtl-optimization/105744] [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
                 CC|                            |linkw at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-05-27

--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
Can be reproduced without cross build compiler.

[Bug rtl-optimization/105744] [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

--- Comment #2 from Kewen Lin <linkw at gcc dot gnu.org> ---
This exposes one bug in glibc strncpy power9 implementation

In
https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=sysdeps/powerpc/powerpc64/le/power9/strncpy.S

        lbz     r0,0(r4)
        stb     r0,0(r3)
        addi    r11,r3,1
        addi    r5,r5,-1
        vspltisb v18,0          /* Zeroes in v18  */

...

L(zero_padding_end):
        sldi    r10,r5,56       /* stxvl wants size in top 8 bits  */
        stxvl   v18,r11,r10     /* Partial store  */
        blr

The code at label "zero_padding_end" is supposed to use v18, but the stxvl will
take the 18 as vsx No. instead of vr No, so it ends up to use the wrong
register vs18 instead of v18 for the store.

The reason why the optimization option matters is that some optimization happen
to generate some sequence to modify the value of vs18 then it's not expected to
be zero any more.

[Bug rtl-optimization/105744] [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tuliom at ascii dot art.br

--- Comment #3 from Kewen Lin <linkw at gcc dot gnu.org> ---
Hi Zdenek,

Could you please double check the strncpy implementation on your side? and help
to file one glibc issue if so.

One further reduced test case:

#define N 3
char a[N];
char c[N];

int
main (void)
{
  asm volatile("xxspltib 18, 0xf" : : :"vs18");
  __builtin_strncpy (c, a, N);
  if (c[0] || c[1])
    __builtin_abort ();
  return 0;
}

[Bug rtl-optimization/105744] [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

--- Comment #4 from Zdenek Sojka <zsojka at seznam dot cz> ---
(In reply to Kewen Lin from comment #3)
> Hi Zdenek,
> 
> Could you please double check the strncpy implementation on your side? and
> help to file one glibc issue if so.
> 
> One further reduced test case:
> 
> #define N 3
> char a[N];
> char c[N];
> 
> int
> main (void)
> {
>   asm volatile("xxspltib 18, 0xf" : : :"vs18");
>   __builtin_strncpy (c, a, N);
>   if (c[0] || c[1])
>     __builtin_abort ();
>   return 0;
> }

Hello Kewen,

thank you for the simple testcase. I can confirm it fails for me, and I am
using the problematic strncpy implementation:

...
   0x0000000010022f10 <+16>:      lbz     r0,0(r4)
   0x0000000010022f14 <+20>:      stb     r0,0(r3)
   0x0000000010022f18 <+24>:      addi    r11,r3,1
   0x0000000010022f1c <+28>:      addi    r5,r5,-1
   0x0000000010022f20 <+32>:      vspltisb v18,0
...
   0x000000001002319c <+668>:     rldicr  r10,r5,56,7
   0x00000000100231a0 <+672>:     stxvl   vs18,r11,r10
   0x00000000100231a4 <+676>:     blr

The code was added to the glibc tree only 18 months ago, so it might explain
why this wasn't triggered before.

I will open a glibc PR for this.

Many thanks,
Zdenek

[Bug rtl-optimization/105744] [11/12/13 Regression] wrong code with -fexpensive-optimizations -flive-range-shrinkage on powerpc64le-unknown-linux-gnu

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105744

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|NEW                         |RESOLVED

--- Comment #5 from Kewen Lin <linkw at gcc dot gnu.org> ---
> 
> I will open a glibc PR for this.
> 

Nice, thanks Zdenek! Changing the status ...