[Bug target/71419] interrupt attribute silently dropped for Thumb code on armv7-a

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71419

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|wrong-code                  |documentation
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-06-06
                 CC|                            |ktkachov at gcc dot gnu.org
      Known to work|5.3.0                       |
            Summary|[6/7 Regression] cortex-a9  |interrupt attribute
                   |IRQ                         |silently dropped for Thumb
                   |                            |code on armv7-a
     Ever confirmed|0                           |1

--- Comment #1 from ktkachov at gcc dot gnu.org ---
The interrupt attribute only works for arm mode i.e. compile with -marm.
That is because the LDM with exception return instruction is only available in
ARM mode. For Thumb mode the attribute is silently ignored.

That being said, we could handle it better. Currently for -mthumb the attribute
still blocks tailcall optimisation, which it shouldn't do if it was properly
ignored.

So we could perhaps issue a warning or error in this situation, document the
behaviour and properly discard the attribute when this occurs