[Bug inline-asm/51423] New: Questions regarding Clobber List for inline ARM/NEON assembly

[Bug inline-asm/51423] New: Questions regarding Clobber List for inline ARM/NEON assembly

[amit_chauhan21 at yahoo dot co.in]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51423

             Bug #: 51423
           Summary: Questions regarding Clobber List for inline ARM/NEON
                    assembly
    Classification: Unclassified
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: inline-asm
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: amit_chauhan21@yahoo.co.in


Dear All,

I am facing some random crashes in my applications on using the neon(inline)
assembly code. However with pure C code the application works fine. I had
following questions regarding neon inline assembly usage.


Q1> In Inline neon assembly does only d8-d15 registers are required to be added
in clobber list even if inline assembly uses d0-d7,d16-d31 registers?

Q2> Correct way to put the register in clobber list: s(32 bit) , d(64 bit) or
q(128bit) registers.

Thanks in Advanced.

[Bug inline-asm/51423] Questions regarding Clobber List for inline ARM/NEON assembly

[rearnsha at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51423

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

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

--- Comment #1 from Richard Earnshaw <rearnsha at gcc dot gnu.org> 2011-12-05 16:22:14 UTC ---
Bugzilla is for reporting bugs, please use gcc-help@gcc.gnu.org for questions.

If you use specific registers in an ASM statement you have to declare all of
them, even if the register is call-clobbered.  The compiler does not try to
parse the contents of the asm statement (it does simple substitution of the
declared operands) so if you don't specify which registers you are modifying
the compiler might try to use them for other purposes.

In GCC-4.5 and earlier you have to specify the smallest addressable register
unit in any clobber list (so s0...s31 and d16...d31)[1].  GCC-4.6 and later are
smarter: the compiler now knows that q0 is equivalent to d0+d1 is equivalent to
s0+s1+s2+s3 etc.

[1] in these older compilers saying "q0" or "d0" will be interpreted as "s0"
and not clobber what you think it should.