Re: [PATCH] Perform case-insensitive comparison when decoding register names (PR target/70320)

[Jozef Lawrynowicz <jozef.l@mittosystems.com>]

On Mon, 08 Jul 2019 21:14:36 +0100
Richard Sandiford <richard.sandiford@arm.com> wrote:

> Segher Boessenkool <segher@kernel.crashing.org> writes:
> > On Thu, Jul 04, 2019 at 01:32:59PM +0100, Jozef Lawrynowicz wrote:  
> >> The attached patch allows the case of register names used in an asm statement
> >> clobber list to be disregarded when checking the validity of the register names.
> >> 
> >> Currently, the register name used in asm statement clobber list must exactly
> >> match those defined in the targets REGISTER_NAMES macro.  
> >  
> >> All the register names defined in the msp430 REGISTER_NAMES macro use an
> >> upper case 'R', so use of lower case 'r' gets rejected.
> >> 
> >> I guess this could also be fixed by defining all the registers in
> >> ADDITIONAL_REGISTER_NAMES using a lower case r, but I prefer this generic
> >> solution and I cannot think of any negative side effects to what is proposed.  
> >
> > It isn't obviously safe either.  Are there any targets that have names
> > for different registers that differ only in case?  You could say that
> > such a design deserves what is coming for it, but :-)

Indeed, I did have a read through all the definitions of REGISTER_NAMES in the
gcc/config and could not spot any cases where different register nanes differed
only in their case. I didn't check it programmatically though, so it's
not impossible I missed something..

> >  
> >> --- a/gcc/varasm.c
> >> +++ b/gcc/varasm.c
> >> @@ -947,7 +947,7 @@ decode_reg_name_and_count (const char *asmspec, int *pnregs)  
> >
> > This is used for more than just clobber lists.  Is this change safe, and
> > a good thing, in the other contexts where it changes things?

It appears to be used for only two purposes (mostly via the
"decode_reg_name" wrapper):
- Decoding the register name in an asm spec and reporting any misuse
- Decoding parameters passed to command line options
Generic options using it are -fcall-used/saved-REG and -ffixed-REG
-fstack-limit-register.
Backends use it for target specific options such as -mfixed-range= for SPU.
Apart from that there appears to be a single other use of it in make_decl_rtl
to report when "register name given for non-register variable", although I
could not immediately reproduce this myself to understand this specific case it
is triggered for.

> >  
> >> -      if (!strcmp (asmspec, "memory"))
> >> +      if (!strcasecmp (asmspec, "memory"))
> >>  	return -4;
> >>  
> >> -      if (!strcmp (asmspec, "cc"))
> >> +      if (!strcasecmp (asmspec, "cc"))
> >>  	return -3;  
> >
> > You don't need to change these.  
> 
> Agreed.  There's also the problem that if we make this available for
> all targets now, people might start using it without realising that
> it implicitly requires GCC 10+.
> 
> But having the feature opt-in (by a DEFHOOKPOD?) sounds good, and
> definitely more maintainable than having to add aliases in the
> target code.
> 
> Thanks,
> Richard

Ok, yes a DEFHOOKPOD or similar sounds like a good idea, I'll look into this
alternative.

Thanks,
Jozef