[Bug middle-end/95464] New: [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[Bug middle-end/95464] New: [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

            Bug ID: 95464
           Summary: [10/11 Regression] Miscompilation of mesa on
                    x86_64-linux since r10-6426
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

Since r10-6426-g5f0653a8b75a5ad5a5405a27dd92d3a5759eed4c we on x86_64-linux
miscompile following testcase at -O2:
struct S { unsigned a:1, b:1, c:1, d:1, e:14, f:14; };

__attribute__((noipa)) int
foo (struct S x)
{
  if (x.a != 0 || x.b != 1 || x.c != 0 || x.d != 1
      || x.e != 7239 || x.f != 6474)
    __builtin_abort ();
}

__attribute__((noipa)) void
bar (struct S x, struct S y)
{
  if (x.a != 0 || x.b != 1 || x.c != 0 || x.d != 1
      || x.e != 7239 || x.f != 6474)
    __builtin_abort ();
  if (y.a != 0 || y.b != 1 || y.c != 1 || y.d != 1
      || y.e != 16320 || y.f != 7315)
    __builtin_abort ();
}

__attribute__((noipa)) void
baz (struct S x)
{
  if (x.a != 1 || x.b != 1 || x.c != 1 || x.d != 1
      || x.e != 16320 || x.f != 7315)
    __builtin_abort ();
}

__attribute__((noipa)) void
qux (struct S x, struct S y, unsigned z)
{
  struct S a = x, b;
  for (unsigned i = 0; i < z; ++i)
    foo (x);
  if (x.a && x.e == 16)
    a.e = 32;
  b = a;
  b.c = y.c;
  b.e = y.e;
  b.f = y.f;
  bar (a, b);
  a = b;
  __asm volatile ("" : : : "ax", "bx", "cx", "dx", "si", "di",
#ifdef __OPTIMIZE__
                           "bp",
#endif
                           "r8", "r9", "r10", "r11", "r12", "r13", "r14",
"r15");
  a.a = 1;
  a.c = 1;
  baz (a);
}

int
main ()
{
  struct S x = { 0, 1, 0, 1, 7239, 6474 };
  struct S y = { 1, 0, 1, 0, 16320, 7315 };
  qux (x, y, 1);
  return 0;
}

(in original source obviously there was no inline asm, but instead the function
was large enough that the variable got spilled).
I believe this is a RA bug though.  In *.ira we have:
(insn 67 66 68 3 (parallel [
            (set (strict_low_part (subreg:QI (reg/v:SI 94 [ a ]) 0))
                (ior:QI (subreg:QI (reg/v:SI 94 [ a ]) 0)
                    (const_int 5 [0x5])))
            (clobber (reg:CC 17 flags))
        ]) "gallivm2.c":51:3 492 {*iorqi_1_slp}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))
(insn 68 67 69 3 (set (reg:SI 5 di)
        (reg/v:SI 94 [ a ])) "gallivm2.c":51:3 67 {*movsi_internal}
     (expr_list:REG_DEAD (reg/v:SI 94 [ a ])
        (nil)))
which looks good to me, the strict_low_part in there says that the low 8 bits
of pseudo 94 are ored with 5 and the upper 24 bits stay as is (so, in the end
it is the same as SImode |= 5, not really sure why we ended up with that, e.g.
if the loop calling foo is changed into a single call to foo, it doesn't
happen).
But LRA changes this into:
(insn 120 66 67 3 (set (reg:QI 0 ax [137])
        (mem/c:QI (plus:DI (reg/f:DI 7 sp)
                (const_int 8 [0x8])) [4 %sfp+-8 S1 A32])) "gallivm2.c":51:3 69
{*movqi_internal}
     (nil))
(insn 67 120 121 3 (parallel [
            (set (strict_low_part (reg:QI 0 ax [137]))
                (ior:QI (reg:QI 0 ax [137])
                    (const_int 5 [0x5])))
            (clobber (reg:CC 17 flags))
        ]) "gallivm2.c":51:3 492 {*iorqi_1_slp}
     (nil))
(insn 121 67 122 3 (set (reg:QI 5 di [orig:94 a ] [94])
        (reg:QI 0 ax [137])) "gallivm2.c":51:3 69 {*movqi_internal}
     (nil))
which is not equivalent, because it makes the upper 24 bits undefined instead
of  loaded from the spill slot.

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-06-01
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
           Keywords|                            |ra, wrong-code
                 CC|                            |vmakarov at gcc dot gnu.org
           Priority|P3                          |P2
   Target Milestone|---                         |10.2

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[vmakarov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #1 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
Jakub, thank you for working on the PR and providing the test case.

It seems to me that the problem occurs in inheritance sub-pass of LRA.  It is a
very complicated sub-pass.  Making a fix and testing it can take a few days. 
But I hope to fix the PR on this week.

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I wonder where we'd simplify things like

(insn 67 66 68 3 (parallel [
            (set (strict_low_part (subreg:QI (reg/v:SI 94 [ a ]) 0))
                (ior:QI (subreg:QI (reg/v:SI 94 [ a ]) 0)
                    (const_int 5 [0x5])))
            (clobber (reg:CC 17 flags))
        ]) "gallivm2.c":51:3 492 {*iorqi_1_slp}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))

I guess simplify_rtx would just see the SET_SRC?  The above might appear
quite frequently from bit fiddling RTL expansion I guess.

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |uros at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Perhaps define_split?  For xor and and too.

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Vladimir Makarov <vmakarov@gcc.gnu.org>:

https://gcc.gnu.org/g:5261cf8ce824bfc75eb6f12ad5e3716c085b6f9a

commit r11-937-g5261cf8ce824bfc75eb6f12ad5e3716c085b6f9a
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Jun 4 12:04:48 2020 -0400

    Add processing STRICT_LOW_PART for matched reloads.

    2020-06-04  Vladimir Makarov  <vmakarov@redhat.com>

            PR middle-end/95464
            * lra.c (lra_emit_move): Add processing STRICT_LOW_PART.
            * lra-constraints.c (match_reload): Use STRICT_LOW_PART in output
            reload if the original insn has it too.

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Vladimir Makarov <vmakarov@gcc.gnu.org>:

https://gcc.gnu.org/g:e7ef9a40cd0c688cd331bc26224d1fbe360c1fe6

commit r11-951-ge7ef9a40cd0c688cd331bc26224d1fbe360c1fe6
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Jun 4 13:32:24 2020 -0400

    Add test for PR95464.c.

    2020-06-04  Vladimir Makarov  <vmakarov@redhat.com>

            PR middle-end/95464
            * gcc.target/i386/pr95464.c: New.

[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.2                        |10.3

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10.2 is released, adjusting target milestone.

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11 Regression]          |[10 Regression]
                   |Miscompilation of mesa on   |Miscompilation of mesa on
                   |x86_64-linux since r10-6426 |x86_64-linux since r10-6426
           Assignee|unassigned at gcc dot gnu.org      |vmakarov at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Vlad, do you plan to backport this to 10.3?

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[vmakarov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #8 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #7)
> Vlad, do you plan to backport this to 10.3?

I guess so.  We had enough time to test it.  I don't see any complaints about
this patch.  I'll backport it today into release/gcc-10 branch.

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Vladimir Makarov
<vmakarov@gcc.gnu.org>:

https://gcc.gnu.org/g:038b65f378b36624b1fd3867fa5e578c1bfa50cc

commit r10-8799-g038b65f378b36624b1fd3867fa5e578c1bfa50cc
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Jun 4 12:04:48 2020 -0400

    Add processing STRICT_LOW_PART for matched reloads.

    2020-06-04  Vladimir Makarov  <vmakarov@redhat.com>

            PR middle-end/95464
            * lra.c (lra_emit_move): Add processing STRICT_LOW_PART.
            * lra-constraints.c (match_reload): Use STRICT_LOW_PART in output
            reload if the original insn has it too.

    (cherry picked from commit 5261cf8ce824bfc75eb6f12ad5e3716c085b6f9a)

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Vladimir Makarov
<vmakarov@gcc.gnu.org>:

https://gcc.gnu.org/g:957e37ac288fe6c40ee0bb98a0b06a85be8a35e3

commit r10-8800-g957e37ac288fe6c40ee0bb98a0b06a85be8a35e3
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Jun 4 13:32:24 2020 -0400

    Add test for PR95464.c.

    2020-06-04  Vladimir Makarov  <vmakarov@redhat.com>

            PR middle-end/95464
            * gcc.target/i386/pr95464.c: New.

    (cherry picked from commit e7ef9a40cd0c688cd331bc26224d1fbe360c1fe6)

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[vmakarov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #11 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #7)
> Vlad, do you plan to backport this to 10.3?

Unfortunately, a few days ago people reported a serious problem with the patch
(see PR97313).  I've just submitted a patch fixing the new problem

https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=bb37ad8cc0fc937c7afcdab471e5d65d176041c3

I believe this new patch should be also cherry-picked to gcc-10 branch.

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Certainly.

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[vmakarov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #13 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #12)
> Certainly.

I've just committed it into the branch
https://gcc.gnu.org/g:70a66ff0228277b4dd89263a663c0a87eb5d782f

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.3                        |10.4

--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10.3 is being released, retargeting bugs to GCC 10.4.

[Bug middle-end/95464] [10 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.2.0
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|10.4                        |10.3

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.