Re: [PATCH 10/27] New file: gcc/jit/libgccjit.c

[David Malcolm <dmalcolm@redhat.com>]

On Mon, 2014-11-03 at 13:32 -0700, Jeff Law wrote:
> On 10/31/14 11:02, David Malcolm wrote:
> > This file implements the entrypoints of the library's public API.
> >
> > It performs error-checking at this boundary, before calling into the
> > jit-recording.h internal API.
> >
> > gcc/jit/
> > 	* libgccjit.c: New.
> > ---
> >   gcc/jit/libgccjit.c | 1506 +++++++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 1506 insertions(+)
> >   create mode 100644 gcc/jit/libgccjit.c
> >
> > +
> > +#define IS_ASCII_ALPHA(CHAR) \
> > +  (					\
> > +    ((CHAR) >= 'a' && (CHAR) <='z')	\
> > +    ||					\
> > +    ((CHAR) >= 'A' && (CHAR) <= 'Z')	\
> > +  )
> > +
> > +#define IS_ASCII_DIGIT(CHAR) \
> > +  ((CHAR) >= '0' && (CHAR) <='9')
> > +
> > +#define IS_ASCII_ALNUM(CHAR) \
> > +  (IS_ASCII_ALPHA (CHAR) || IS_ASCII_DIGIT (CHAR))
> Can't we rely on the C library to give us equivalents?

I've been burned in the past by the C library using locales, in
particular the two lowercase "i" variants in Turkish.

These macros are used by gcc_jit_context_new_function to enforce C's
naming restrictions, to avoid errors from the assembler.  The comment I
put there was:

  /* The assembler can only handle certain names, so for now, enforce
     C's rules for identifiers upon the name.
     Eventually we'll need some way to interact with e.g. C++ name mangling.  */

Am I right in thinking that for the assembler we need to enforce the C
naming rules specifically on *ASCII*.

(clearly another comment is needed here).

> > +
> > +/* TODO: mark failure branches as unlikely? */
> > +
> Not likely worth the effort.  And it'd be better to somehow mark 
> jit_error such that anytime a path unconditionally calls jit_error, the 
> whole path is considered unlikely.

(nods)

> I think it was Ball & Larus that had a predictor of this nature, I don't 
> recall its effectiveness offhand.  But I'd rather be marking the 
> function than sprinlkling unlikely all over the actual codepaths.

Presumably by marking it with __attribute__((cold)) ?  (with a suitable
macro in case we're not being compiled with a gcc that supports it).

I suspect doing so will be of more use in teaching me about gcc
internals and the effect on generated code that in measurable benefits
to said code in this case :)

> > +static bool
> > +compatible_types (gcc::jit::recording::type *ltype,
> > +		  gcc::jit::recording::type *rtype)
> All function definitions should have a block comment describing the 
> function and its arguments.   This comment applies throughout the code 
> and needs to be addressed prior to commit.  In fact I really can't even 
> continue review of this code due to the lack of comments -- I rely 
> heavily on them.

Sorry.  I'll post a followup with comments added.

Many of the functions are public API entrypoints, where there's a
comment in the public header.  Should I simply duplicate the comment
from there into the .c file, or put a comment like:

  /* Public entrypoint.  See description in libgccjit.h.  */

for each of these?  (perhaps with additional text giving implementation
notes?)


Thanks for all the reviews.  Looks like this and patch 16 are now the
only non-approved parts of the kit (I didn't see a review of 16).

Dave