[Bug target/94177] New: TLS global-dynamic model clobbers function parameter on AIX

[Bug target/94177] New: TLS global-dynamic model clobbers function parameter on AIX

[dje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94177

            Bug ID: 94177
           Summary: TLS global-dynamic model clobbers function parameter
                    on AIX
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dje at gcc dot gnu.org
  Target Milestone: ---
            Target: powerpc-ibm-aix*

In global-dynamic model, if a TLS variable first is referenced in the argument
list to a function call, GCC can load the parameters to the call before
invoking the function to legitimize the TLS variable, and the legitimize
function clobbers some of the same function argument registers.

extern int foo (char *, int *, int);

int main()
{
   static __thread int result;

   foo ("%p %u\n", &result, 169);
   return 0;
}

$ gcc -fPIC -S bug_tls.c
        li 5,169
        lwz 10,LCM..1(2)
        lwz 9,LC..1(2)
        mr 3,10
        mr 4,9
        bla __tls_get_addr <*** clobbers r4, r5 already loaded with arguments
to foo
        mr 9,3
        mr 4,9
        lwz 3,LC..2(2)
        bl .foo


The pattern that generates __tls_get_addr shows that it clobbers r4 and r5

(define_insn "tls_get_addr_internal<mode>"
  [(set (reg:P 3)
        (unspec:P [(reg:P 3) (reg:P 4)] UNSPEC_TLSTLS))
   (clobber (reg:P 0))
   (clobber (reg:P 4))
   (clobber (reg:P 5))
   (clobber (reg:P 11))
   (clobber (reg:CC CR0_REGNO))
   (clobber (reg:P LR_REGNO))]
  "TARGET_XCOFF && HAVE_AS_TLS"
  "bla __tls_get_addr")

but GCC overwrites the parameters in calls.c during initial RTL generation.

[Bug target/94177] TLS global-dynamic model clobbers function parameter on AIX

[dje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94177

David Edelsohn <dje at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-03-09
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from David Edelsohn <dje at gcc dot gnu.org> ---
Confirmed.

[Bug target/94177] TLS global-dynamic model clobbers function parameter on AIX

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94177

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Edelsohn <dje@gcc.gnu.org>:

https://gcc.gnu.org/g:a21b399708175f6fc0ac723a0cebc127da421c60

commit r12-165-ga21b399708175f6fc0ac723a0cebc127da421c60
Author: David Edelsohn <dje.gcc@gmail.com>
Date:   Sun Apr 11 19:41:26 2021 -0400

    aix: TLS precompute register parameters (PR 94177)

    AIX uses a compiler-managed TOC for global data, including TLS symbols.
    The GCC TOC implementation manages the TOC entries through the constant
pool.

    TLS symbols sometimes require a function call to obtain the TLS base
    pointer.  The arguments to the TLS call can conflict with arguments to
    a normal function call if the TLS symbol is an argument in the normal call.
    GCC specifically checks for this situation and precomputes the TLS
    arguments, but the mechanism to check for this requirement utilizes
    legitimate_constant_p().  The necessary result of legitimate_constant_p()
    for correct TOC behavior and for correct TLS argument behavior is in
    conflict.

    This patch adds a new target hook precompute_tls_p() to decide if an
    argument should be precomputed regardless of the result from
    legitmate_constant_p().

    gcc/ChangeLog:

            PR target/94177
            * calls.c (precompute_register_parameters): Additionally test
            targetm.precompute_tls_p to pre-compute argument.
            * config/rs6000/aix.h (TARGET_PRECOMPUTE_TLS_P): Define.
            * config/rs6000/rs6000.c (rs6000_aix_precompute_tls_p): New.
            * target.def (precompute_tls_p): New.
            * doc/tm.texi.in (TARGET_PRECOMPUTE_TLS_P): Add hook documentation.
            * doc/tm.texi: Regenerated.

[Bug target/94177] TLS global-dynamic model clobbers function parameter on AIX

[dje at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94177

David Edelsohn <dje at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |12.0

--- Comment #3 from David Edelsohn <dje at gcc dot gnu.org> ---
Fixed.

[Bug target/94177] TLS global-dynamic model clobbers function parameter on AIX

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94177

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by David Edelsohn
<dje@gcc.gnu.org>:

https://gcc.gnu.org/g:0be51abf080f1d7515e3777dd5e5a983b47573a8

commit r11-8481-g0be51abf080f1d7515e3777dd5e5a983b47573a8
Author: David Edelsohn <dje.gcc@gmail.com>
Date:   Fri Apr 30 14:27:46 2021 -0400

    aix: TLS precompute register parameters (PR 94177)

    AIX uses a compiler-managed TOC for global data, including TLS symbols.
    The GCC TOC implementation manages the TOC entries through the constant
pool.

    TLS symbols sometimes require a function call to obtain the TLS base
    pointer.  The arguments to the TLS call can conflict with arguments to
    a normal function call if the TLS symbol is an argument in the normal call.
    GCC specifically checks for this situation and precomputes the TLS
    arguments, but the mechanism to check for this requirement utilizes
    legitimate_constant_p().  The necessary result of legitimate_constant_p()
    for correct TOC behavior and for correct TLS argument behavior is in
    conflict.

    This patch adds a new target hook precompute_tls_p() to decide if an
    argument should be precomputed regardless of the result from
    legitmate_constant_p().

    gcc/ChangeLog:

            PR target/94177
            * calls.c (precompute_register_parameters): Additionally test
            targetm.precompute_tls_p to pre-compute argument.
            * config/rs6000/aix.h (TARGET_PRECOMPUTE_TLS_P): Define.
            * config/rs6000/rs6000.c (rs6000_aix_precompute_tls_p): New.
            * target.def (precompute_tls_p): New.
            * doc/tm.texi.in (TARGET_PRECOMPUTE_TLS_P): Add hook documentation.
            * doc/tm.texi: Regenerated.

            (cherry-picked from commit
a21b399708175f6fc0ac723a0cebc127da421c60)