Re: [PATCH, committed] PPC405 atomic support (PR target/21760)

[Geoffrey Keating <geoffk at geoffk dot org>]

David Edelsohn <dje@watson.ibm.com> writes:

> >>>>> Andreas Schwab writes:
> 
> >> + /* If configured for PPC405, support PPC405CR Erratum77.  */
> >> + #define PPC405_CPU_DEFAULT ("405")
> >> + #if #TARGET_CPU_DEFAULT == #PPC405_CPU_DEFAULT
> 
> Andreas> What is this expression supposed to do?  It doesn't match
> anything defined by C89.
> 
> 	The expression is comparing the stringified value of the macros.

I'm pretty sure that doesn't work, and in fact should be an error;
even C99 says that "The expression that controls conditional inclusion
shall be an integer constant expression" (and I think the "shall" in
this location requires a diagnostic).  I filed

<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22168>

to track it.

I think you might be able to get away with

#define ppc405_is_default (strcmp(TARGET_CPU_DEFAULT, "405") == 0)

with no cost at runtime, since gcc will fold the strcmp.