[llvm-dev] Getting SMLoc from debug metadata

[Min-Yih Hsu via llvm-dev]

Hi,

To my best understanding, you want to emit diagnostic that shows the line, column, and the input source code (in your case the swift-alike language) whenever you encounter an error while processing the LLVM IR inside the middle-end. I’m afraid this is difficult to fit into SMLoc / SourceMgr’s original design.

SMLoc is just a pointer into a buffer, which contains the source code, maintained by llvm::SourceMgr, that’s why you cannot print out full diagnostic string without the help of SourceMgr. Thus if you want to leverage SMLoc / SourceMgr, the buffer needs to carry the source code of your input language. However, LLVM’s compilation pipeline does not assume the input source code to be available inside the middle-end. The frontend and the middle-end are two separated entities communicated only by the IR.
So unless you load your input code into SourceMgr inside the middle-end, there is no way to use SMLoc for diagnosing the input code. But then I guess another (much more difficult) question will be: How do you map from high-level code to low level LLVM IR (after the input code is loaded into SourceMgr)?

The debug info you mentioned _might_ be a way, but currently there is no way to use the DebugInfo infrastructure with SMLoc.

And just a FYI, SMLoc is primarily used in emitting diagnostic info while parsing textual LLVM IR (e.g. Pop an error when there is an ill-form LLVM IR syntax)

-Min

> On Nov 2, 2021, at 7:28 AM, Carl Peto via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> I’m trying to create something like an LLVM pass fairly low in my compiler (a variant of swift).
> 
> I have an llvm::Function and llvm::Instruction where I want to emit diagnostics, using swift’s built in diagnostics system. That means I think I need an SMLoc.
> 
> I’ve used getDebugLoc().get(); to get the DILocation and can getLine(), getColumn() etc. from there to get the source location as a filename, line and column, which seems accurate enough.
> 
> 
> I’m trying to figure out how to then create an SMLoc from that. The SMLoc class only seems to take a pointer in the constructor, which I don’t understand.
> 
> Sorry I couldn’t figure this out by googling!
> 
> Carl
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev