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Subject: [Bug target/50305] New: Inline asm reload failure when building Linux kernel
Date: Tue, 06 Sep 2011 17:07:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D50305

             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=3D25204
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=3Darmv7-a

core.i: In function =E2=80=98event_alloc=E2=80=99:
core.i:34:2: error: =E2=80=98asm=E2=80=99 operand requires impossible reload
core.i:34:2: error: =E2=80=98asm=E2=80=99 operand requires impossible reload

Note that while the inline asm may be somewhat inefficient (enforcing a "+Q=
o"
constraint on an operand that is never used in the assembly), there is noth=
ing
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.