[LLVMdev] inline asm constraints in LLVM
dalej at apple.com
Thu Jul 29 11:41:39 PDT 2010
The LLVM asm parser doesn't support multiple alternative constraints;
you need to have Clang pick one tuple in the front end. See
ChooseConstraintTuple in llvm-gcc for prior art.
On Jul 29, 2010, at 11:36 AMPDT, John Thompson wrote:
> I'm trying to fix the handling of multiple alternate constraints in
> Clang (see http://gcc.gnu.org/onlinedocs/gcc/Multi_002dAlternative.html#Multi_002dAlternative)
> How should the constraints be represented in the .ll file?
> Clang currently will assert because the code generator sees a
> constraints string with the wrong number of comma-separated items.
> Basically, after some editing, it just concatenates them together.
> The commas used in the string for a multiple alternative constraint
> gets confused with the commas separating the constraints.
> Briefly looking at the LLVM asm parser, I can't really see anything
> that tells me multiple alternative constraints are supported.
> But if they are, please tell me the string format, and perhaps
> update the docs to show this.
> If they are not yet supported in LLVM, what should I do?
> John Thompson
> John.Thompson.JTSoftware at gmail.com
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
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