[cfe-dev] Diagnostic source location accuracy with and without remarks enabled

[Paul Kirth via cfe-dev]

On Fri, Aug 16, 2019 at 9:56 PM Adam Nemet <anemet at apple.com> wrote:

>
>
> On Aug 16, 2019, at 8:17 PM, Paul Kirth <paulkirth at google.com> wrote:
>
> I'm trying to get some insight into why source locations in a warning
> resolve differently when remarks are enabled in a cc1 invocation.
>
> In a diagnostic handler I have two diagnostics being emitted(one warning
> and one remark), but the accuracy of the source location changes
> dramatically if I request remarks to be emitted through '-R<remark>'. Note
> that I don't mean the specific remark I'm emitting, I mean *any* remark.
>
> More concretely, when I enable the warning and request no remarks, I get a
> source location that is the beginning of the function. However, if I enable
> any remarks(such as for the inliner pass), the source location becomes
> fully accurate for the warning(i.e. pointing to a branch location in the
> function body).
>
>
> Requesting remarks implies -gline-tables-only.
>
>
Thanks for the clarification, that makes more sense.


> Adam
>
>
> The invocations only differ in a small way:
>
> clang -cc1 source.ll -Wmisexpect <... rest of invocation>
>
> vs.
>
> clang -cc1 source.ll -Wmisexpect -R<anything> <... rest of invocation>
>
> I ran into this when working on some tests in
> https://reviews.llvm.org/D66324, and I'm having trouble understanding why
> this is happening. The same source location is passed to both diagnostics.
> This behavior also doesn't seem to appear if I don't use cc1 directly, but
> I would still like to understand this behavior.
>
> Can someone explain why enabling remarks here has an effect on the
> accuracy of the source locations? Do they cause a delay in the source
> location resolution, or is there an important piece of infrastructure that
> the remarks framework enables that I've missed?
>
> For reference my backend diagnostic handler looks something like the
> following snippet where the source location is passed to both the warning
> and remark:
>
> ```
> void BackendConsumer::MisExpectDiagHandler(
>     const llvm::DiagnosticInfoMisExpect &D) {
>   StringRef Filename;
>   unsigned Line, Column;
>   bool BadDebugInfo = false;
>   FullSourceLoc Loc =
>       getBestLocationFromDebugLoc(D, BadDebugInfo, Filename, Line, Column);
>
>   Diags.Report(Loc, diag::warn_misexpect) << D.getMsg().str();
>   Diags.Report(Loc, diag::remark_misexpect) << D.getMsg().str();
>
>   // ...
> }
> ```
>
>
> --
> Paul Kirth
>
>
>

-- 
Paul Kirth
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