[Bug target/52125] Problems with LO16 asm operands on MIPS

[Bug target/52125] Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

rsandifo@gcc.gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |mips*-*-*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-02-05
     Ever Confirmed|0                           |1

[Bug target/52125] New: Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

             Bug #: 52125
           Summary: Problems with LO16 asm operands on MIPS
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rsandifo@gcc.gnu.org


On MIPS, the "m" asm constraint allows %lo16 addresses.
This can cause orphaned HI16 relocations on REL targets
if the memory operand isn't actually referenced in the
asm string, but is simply there to record that a particular
piece of memory is used or set.  This can be seen in
gcc/testsuite/gcc.dg/pr48774.c.

It's difficult to know what to do here.  On the one hand,
passing any mem to "m" in this way ought to work, so it is
a genuine bug.  On the other hand, I think "m" has allowed
LO16 addresses since -msplit-addresses was added all those
years ago, and I can't remember any complaints about it
causing problems in "real" code.  It would only cause
problems in cases where the CU has no other LO16 references
to the same address (or the same address plus a constant).

We could forbid LO16 "m" references on REL targets and provide
a new memory constraint that allows them, but that might
cause unnecessary pessimisation of working asm statements.
People who want the best performance would have to conditionalise
their code based on the GCC version, using "m" for old versions
and the proposed constraint for new versions.

Since this isn't a 4.7 regression, I'm not planning on
doing anything at this stage.

[Bug target/52125] Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

--- Comment #1 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> 2012-02-05 14:56:39 UTC ---
Author: rsandifo
Date: Sun Feb  5 14:56:35 2012
New Revision: 183910

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=183910
Log:
gcc/testsuite/
    PR target/52125
    * lib/target-supports.exp (check_effective_target_mips_rel): New.
    * gcc.dg/pr48774.c: Skip on MIPS REL targets.

Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/pr48774.c
    trunk/gcc/testsuite/lib/target-supports.exp

[Bug target/52125] Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rsandifo at gcc dot gnu.org

--- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Testing a patch.

[Bug target/52125] Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

--- Comment #3 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Author: rsandifo
Date: Thu Jan 23 08:24:38 2014
New Revision: 206955

URL: http://gcc.gnu.org/viewcvs?rev=206955&root=gcc&view=rev
Log:
gcc/
    PR target/52125
    * rtl.h (get_referenced_operands): Declare.
    * recog.c (get_referenced_operands): New function.
    * config/mips/mips.c (mips_reorg_process_insns): Check which asm
    operands have been referenced when recording LO_SUM references.

gcc/testsuite/
    PR target/52125
    * gcc.dg/pr48774.c: Remove skip for mips_rel.
    * gcc.target/mips/pr52125.c: New test.

Added:
    trunk/gcc/testsuite/gcc.target/mips/pr52125.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/mips/mips.c
    trunk/gcc/recog.c
    trunk/gcc/rtl.h
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/pr48774.c

[Bug target/52125] Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

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

--- Comment #4 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Fixed on trunk.  Not a regression, so probably not backport material.

[Bug target/52125] Problems with LO16 asm operands on MIPS

[sje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

Steve Ellcey <sje at gcc dot gnu.org> changed:

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

--- Comment #5 from Steve Ellcey <sje at gcc dot gnu.org> ---
The new test (gcc.target/mips/pr52125.c) is passing on my linux target
(mips-mti-linux-gnu) but failing for my elf target (mips-mti-elf).  The code
for the asm statement I get on elf is:

#APP
# 8 "pr52125.c" 1
    %gp_rel(b)($28) %gp_rel(d)($28)
# 0 "" 2
#NO_APP

It looks like I can fix this by using -mno-gpopt.  Is this a reasonable
fix or does it break what we want to test?

[Bug target/52125] Problems with LO16 asm operands on MIPS

[rsandifo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

--- Comment #6 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Yeah, got the same thing in overnight mipsisa64-sde-elf testing but
hadn't had chance to look at it.

Adding -mno-gpopt is fine.

[Bug target/52125] Problems with LO16 asm operands on MIPS

[sje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52125

--- Comment #7 from Steve Ellcey <sje at gcc dot gnu.org> ---
OK, I will check that in as an obvious fix.