Re: MIPS JAL/JALR to BAL transformation for Linux (o32 ABI)

[David Daney <ddaney at caviumnetworks dot com>]

Adam Nemet wrote:
> Fu, Chao-Ying writes:
> > > > +/* True if ABFD is for CPUs that are faster if jal/jalr is 
> > > converted to bal.
> > > > +   This should be safe for all architectures, but for now 
> > > we enable it
> > > > +   for RM9000, mips32, mips32r2, mips64, and mips64r2.  */
> > > > +#define JAL_JALR_TO_BAL_P(abfd) \
> > > > +  (   ((elf_elfheader (abfd)->e_flags & EF_MIPS_MACH) == 
> > > E_MIPS_MACH_9000) \
> > > > +   || ((elf_elfheader (abfd)->e_flags & EF_MIPS_ARCH) == 
> > > E_MIPS_ARCH_32) \
> > > > +   || ((elf_elfheader (abfd)->e_flags & EF_MIPS_ARCH) == 
> > > E_MIPS_ARCH_32R2) \
> > > > +   || ((elf_elfheader (abfd)->e_flags & EF_MIPS_ARCH) == 
> > > E_MIPS_ARCH_64) \
> > > > +   || ((elf_elfheader (abfd)->e_flags & EF_MIPS_ARCH) == 
> > > E_MIPS_ARCH_64R2))
> > >
> > > I think this should be a negative predicate.  As you say JALR->BAL
> > > should be a profitable transformation on most CPUs.
> >   Yes.  If everyone is ok, we can just set JAL_JALR_TO_BAL_P(abfd) to 1.
> > (And, fix new test failures due to BAL mismatching.)
>
> Just to be sure, what I said applies to JALR->BAL for Octeon.  JAL->BAL is not
> necessarily profitable on Octeon but I thought the relaxation code was
> performing JALR->BAL or JALR->JAL and not JAL->BAL?  Am I missing something
> here?

In -fPIC code we would want JALR -> BAL, one would hope that JAL would 
not be emitted with -fPIC.  It probably varies on a per CPU basis 
whether or not JAL or BAL is preferable, but if the branch range is 
exceeded you would probably want to fall back to JAL.

David Daney