[RFC v2] Towards an assembler parser for PowerPC

[Ulrich Weigand]

David Fang <fang at csl.cornell.edu> wrote on 14.03.2013 00:32:56:

>     Just wanted to ping and ask how close we are to seeing
> PPCAsmParser.  I've made good progress on the mach-o/PPC backend, but
have
> run into a few blocks.

I've been out sick for the past two weeks and didn't make any progress,
sorry.  But I'm back working on the asm parser now ...

One piece of good news is that Jakob has been looking at some of the
common TableGen changes, and it looks like this is close to getting in.

> 1) lib/Target/PowerPC/PPCAsmPrinter.cpp:PPCDarwinAsmPrinter emits a
> bcl instruction in the stub for dynamically linked functions.
> Would it be easy to MC-ize the bcl (branch-conditional-link) instruction?

Well, at some point we'll have to add the full set of branch instructions
anyway to support the complete instruction set in the parser; I've
considered
that to be a follow-on step after the first instance of the parser gets
committed ...

In any case, adding a new pattern (with isCodeGenOnly = 1) to be
generated by PPCDarwinAsmPrinter ought to be straightforward for now.

For my curiosity:

      OutStreamer.EmitRawText("\tbcl 20, 31, " + Twine(AnonSymbol->getName
()));

bcl 20 ... seems to imply an unconditional branch after all.  Do you
know why this can't just use a plain bl?

> 2) Some of the system C++ headers (4.0.1) have inline asm, so I'm unable
> to compile an <iostream> hello-world using the integrated-assembler.
>
> clang gripes:
> fatal error: error in backend: Inline asm not supported by this streamer
> because we don't have an asm parser for this target
>
> (A <stdio.h> version in C works though.)
> I assume the PPC asm parser will solve this?

Yes, this should be supported with the asm parser.  (Of course, assuming
that the particular instructions used in those inline asm statements are
already supported.)

Bye,
Ulrich