[llvm-dev] TableGen - cryptic error messages (~feature request)

[David Blaikie via llvm-dev]

On Tue, Dec 29, 2015 at 2:54 PM, RCU via llvm-dev <llvm-dev at lists.llvm.org>
wrote:

>   Hello.
>     I started implementing a back end in LLVM (and I'm writing some hints
> I consider useful at
> https://sites.google.com/site/alexsusu/home/backend-llvm ).
>     Unfortunately, I hit quite a few times very cryptic error messages
> when compiling with TableGen, which required a few good hours of debugging
> the TableGen program.
>
>     The most cryptic error message was when compiling with TableGen, with
> the option -gen-asm-matcher . Here I got the following error message:
> llvm-tblgen: ~/llvm/lib/TableGen/StringMatcher.cpp:52: bool
> llvm::StringMatcher::EmitStringMatcherForChar(const std::vector<const
> std::pair<std::basic_string<char>, std::basic_string<char> >*>&, unsigned
> int, unsigned int) const: Assertion `Matches.size() == 1 && "Had duplicate
> keys to match on"' failed.
> [...]
> Stack dump:
> 0.      Program arguments: ~/llvm/build3/bin/llvm-tblgen -gen-asm-matcher
> -I ~/llvm/include Connex.td
> ./run_tblgen.sh: line 13: 27011 Aborted                 (core dumped)
> ~/llvm/build3/bin/llvm-tblgen -gen-asm-matcher -I ~/llvm/include Connex.td
> > ConnexGenAsmMatcher.inc
>
>     It took me quite a few hours to find the source of the error, namely
> the fact I had defined two registers with the SAME ASM name (string) - so
> the disassembly (ASM matcher) info had conflicts. I actually sped up my
> debugging by editing the file ~/llvm/lib/TableGen/StringMatcher.cpp and
> adding in StringMatcher::
> EmitStringMatcherForChar() some printing that explained more clearly why
> the error happens.
>
>     Therefore I have this IMPORTANT question: would you feel it is useful
> to make TableGen give more detailed error messages? I personally recommend
> this.
>

Seems reasonable to add some extra text to the assertion (and possibly use
better error handling - not sure if tblgen aspires to be assertion-free on
unbounded table inputs, but it probably should be... ). Perhaps you could
send a patch to llvm-commits to discuss the specifics there?

- Dave


>
>
>   Thank you,
>     Alex
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