[Bug target/50305] New: Inline asm reload failure when building Linux kernel

[Bug target/50305] New: Inline asm reload failure when building Linux kernel

[uweigand at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50305

             Bug #: 50305
           Summary: Inline asm reload failure when building Linux kernel
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: uweigand@gcc.gnu.org
            Target: arm-linux-gnueabi


Created attachment 25204
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25204
Reduced test case

Building the Linux kernel with current mainline fails with certain sets of
options due to a reload failure on an atomic.h inline asm.

The attached test case reproduces the problem when compiled with
  -O2 -fno-omit-frame-pointer -marm -march=armv7-a

core.i: In function ‘event_alloc’:
core.i:34:2: error: ‘asm’ operand requires impossible reload
core.i:34:2: error: ‘asm’ operand requires impossible reload

Note that while the inline asm may be somewhat inefficient (enforcing a "+Qo"
constraint on an operand that is never used in the assembly), there is nothing
invalid about the set of constraints (and there are enough registers
available).

The problem seems instead to be caused by unfortunate interactions between
ARM's legitimize_reload_address routine and subsequent iterations through
find_reloads common code.

[Bug target/50305] Inline asm reload failure when building Linux kernel

[uweigand at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50305

Ulrich Weigand <uweigand at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-09-06
         AssignedTo|unassigned at gcc dot       |uweigand at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #1 from Ulrich Weigand <uweigand at gcc dot gnu.org> 2011-09-06 17:06:45 UTC ---
Created attachment 25205
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25205
Possible fix

I'm currently testing this patch to fix the problem.

[Bug target/50305] Inline asm reload failure when building Linux kernel

[michael.hope at linaro dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50305

Michael Hope <michael.hope at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |michael.hope at linaro dot
                   |                            |org

--- Comment #2 from Michael Hope <michael.hope at linaro dot org> 2011-09-11 21:47:59 UTC ---
Note that the fault goes away with -mfpu=neon and returns with -mfpu=vfpv3. 
You might want to add an explicit fpu to the dg-options.

For reference, I could reproduce the fault in r177688, r178025, r178624, and
gcc-linaro-4.5-2011.08.  It does not exist in 4.5.3, 4.6.1, or
gcc-linaro-4.6-2011.08.

[Bug target/50305] Inline asm reload failure when building Linux kernel

[uweigand at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50305

--- Comment #3 from Ulrich Weigand <uweigand at gcc dot gnu.org> 2011-10-06 11:50:35 UTC ---
Author: uweigand
Date: Thu Oct  6 11:50:26 2011
New Revision: 179603

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=179603
Log:
    gcc/
    PR target/50305
    * config/arm/arm.c (arm_legitimize_reload_address): Recognize
    output of a previous pass through legitimize_reload_address.
    Do not attempt to optimize addresses if the base register is
    equivalent to a constant.

    gcc/testsuite/
    PR target/50305
    * gcc.target/arm/pr50305.c: New test.

Added:
    trunk/gcc/testsuite/gcc.target/arm/pr50305.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/arm/arm.c
    trunk/gcc/testsuite/ChangeLog

[Bug target/50305] Inline asm reload failure when building Linux kernel

[uweigand at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50305

Ulrich Weigand <uweigand at gcc dot gnu.org> changed:

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

--- Comment #4 from Ulrich Weigand <uweigand at gcc dot gnu.org> 2011-10-06 11:53:26 UTC ---
Fixed.