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Bob Frankel

2009-May-04 01:19 UTC

[LLVMdev] leveraging back-end C compiler features in the gcc-based front-end

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<font size="-1"><font face="Verdana">i'm
looking into using llvm with
TI's MSP430, for which a C compiler from TI already exists; the idea
here is to use llc -march=c and then pass the generated C code on to
the TI compiler.  as it turns out, the TI C compiler supports a number
of (processor-specific) intrinsics that expose much of the underlying
CPU architecture directly to the C programmer -- registers,
pseudo-functions for enabling/disabling interrupts and reading/writing
status bits, etc.<br>
<br>
is there a way to leverage these (non-gcc) intrinsics in the llvm
gcc-based frontend -- perhaps flagging their use in such a way that
they effectively "pass through" the optimizer and are emitted "as
is"
in the generated C code?   in some respects, you can think of this
usage as not unlike dropping inline asm code into the C sources.<br>
<br>
bob frankel<br>
<br>
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Eli Friedman

2009-May-04 01:40 UTC

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[LLVMdev] leveraging back-end C compiler features in the gcc-based front-end

On Sun, May 3, 2009 at 6:19 PM, Bob Frankel <bios.bob.frankel at
gmail.com> wrote:> i'm looking into using llvm with TI's MSP430
Ah, you're in luck then: an MSP430 backend was checked in to SVN today
:)  I don't think it's mature enough for general use yet, though.
> is there a way to leverage these (non-gcc) intrinsics in the llvm gcc-based
> frontend -- perhaps flagging their use in such a way that they effectively
> "pass through" the optimizer and are emitted "as is" in
the generated C
> code?   in some respects, you can think of this usage as not unlike
dropping
> inline asm code into the C sources.
You could try just generating calls to the builtins in question; if
you're lucky, it'll just work... if not, you can always use sed (or
equivalent) to manipulate the C output into the correct form.

-Eli

Bob Frankel

2009-May-04 02:12 UTC

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[LLVMdev] leveraging back-end C compiler features in the gcc-based front-end

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<font size="-1"><font face="Verdana">wow!!!  i
would be interested in
trying this....  any helpful instructions (for a novice like me) to get
started using the msp430 backend would be helpful....<br>
<br>
as for your suggestion, it does work -- i can (say) place a call to
__get_SR_register() in my front-end source, and it simply shows up in
the back-end .c file; other "extensions" to compilers (such as
'interrupt' keyword to generate different prologue/epilogue code) would
be a little trickier (though there are presumably already gcc
mechansims for flagging interrupt routines??)<br>
<br>
<br>
</font></font><br>
Eli Friedman wrote:
<blockquote
 cite="mid:f5aa3e9b0905031840j5511e5d2md2144a0438c32379@mail.gmail.com"
 type="cite">
  <pre wrap="">On Sun, May 3, 2009 at 6:19 PM, Bob Frankel <a
class="moz-txt-link-rfc2396E"
href="mailto:bios.bob.frankel@gmail.com"><bios.bob.frankel@gmail.com></a>
wrote:
  </pre>
  <blockquote type="cite">
    <pre wrap="">i'm looking into using llvm with TI's
MSP430
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Ah, you're in luck then: an MSP430 backend was checked in to SVN today
:)  I don't think it's mature enough for general use yet, though.

  </pre>
  <blockquote type="cite">
    <pre wrap="">is there a way to leverage these (non-gcc)
intrinsics in the llvm gcc-based
frontend -- perhaps flagging their use in such a way that they effectively
"pass through" the optimizer and are emitted "as is" in the
generated C
code?   in some respects, you can think of this usage as not unlike dropping
inline asm code into the C sources.
    </pre>
  </blockquote>
  <pre wrap=""><!---->
You could try just generating calls to the builtins in question; if
you're lucky, it'll just work... if not, you can always use sed (or
equivalent) to manipulate the C output into the correct form.

-Eli

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href="http://llvm.cs.uiuc.edu">http://llvm.cs.uiuc.edu</a>
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Anton Korobeynikov

2009-May-04 08:22 UTC

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[LLVMdev] leveraging back-end C compiler features in the gcc-based front-end

Hello, Bob
> supports a number of (processor-specific) intrinsics that expose much of
the
> underlying CPU architecture directly to the C programmer -- registers,
> pseudo-functions for enabling/disabling interrupts and reading/writing
> status bits, etc.Nothing special here. All this can be implemented either via inline
assembler and/or via register-tied variables. I have no idea whether
mspgcc supports this, but this certainly possible.

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

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