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

[James Grosbach via llvm-dev]

> On Jan 7, 2016, at 9:50 AM, David Blaikie via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> 
> 
> On Tue, Dec 29, 2015 at 2:54 PM, RCU via llvm-dev <llvm-dev at lists.llvm.org <mailto: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 <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?

It definitely aspires to, yeah. An assert() for a user error is not a great experience. Patches making that aspiration a bit closer to the reality are very welcome.

-jim

> 
> - Dave
>  
> 
> 
>   Thank you,
>     Alex
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