[PATCH] D73282: Fix debug-info generation for block invocations so that we set the LinkageName instead of the Name

[David Blaikie via Phabricator via cfe-commits]

dblaikie added inline comments.


================
Comment at: clang/lib/CodeGen/CGDebugInfo.cpp:3659
     // Use llvm function name.
-    Name = Fn->getName();
+    if (Fn->getName().startswith("___Z"))
+      LinkageName = Fn->getName();
----------------
shafik wrote:
> dblaikie wrote:
> > shafik wrote:
> > > dblaikie wrote:
> > > > shafik wrote:
> > > > > dblaikie wrote:
> > > > > > aprantl wrote:
> > > > > > > aprantl wrote:
> > > > > > > > Could you please add a comment that Clang Blocks are generated as raw llvm::Functions but do have a mangled name and that is handling this case? Otherwise this would look suspicious.
> > > > > > > Should *all* raw LLVM functions have their name as the linkage name? Perhaps a raw LLVM function should only have a linkage name and no human-readable name?
> > > > > > Seems plausible to me - do we have any data on other types of functions that hit this codepath? 
> > > > > So it was not obvious to me what other cases would this branch so I added an assert and ran `check-clang` and from that I saw four cases that ended up here:
> > > > > 
> > > > > `GenerateCapturedStmtFunction`
> > > > > `GenerateOpenMPCapturedStmtFunction`
> > > > > `GenerateBlockFunction`
> > > > > `generateDestroyHelper`
> > > > > 
> > > > > It is not obvious to me we want to alter the behavior of any of the other cases.
> > > > Could you show any small source examples & their corresponding DWARF & how that DWARF would change? (what names are we using, what names would we end up using/what sort of things are they naming)
> > > Ok, I understand the objections to special casing like this. We ended up setting both the `Name` and `LinkageName` unconditionally in this branch because not setting the name for subroutines end up with us generating `DW_TAG_subprogram` without a `DW_AT_name` which is not valid. We discovered this when running the LLDB test suite.
> > If we need to have a name, and these are mangled names - were they mangled /from/ something & have an unmangled name we should be using, then?
> > 
> > llvm-cxxfilt demangles the example/test as "invocation function for block in f(void (int) block_pointer)" - perhaps we should name this "invocation function"? & let the scope of the DIE communicate the rest of the information about this thing (like the "operator()" for a lambda is just "operator()")?
> If we take the example from the test I added it demangles to:
> 
> ```
> invocation function for block in f(void (int) block_pointer)
> ```
> 
> There is no usable "short" name there, it is a complex description of the block and what wraps it. In general from the LLDB perspective we would want a name to set a breakpoint or display it during a back trace. In this case we care about displaying this properly in a back trace and it would not be reasonable to use such a name to set a breakpoint. 
> 
How's that compare to lambdas, for example?


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  https://reviews.llvm.org/D73282/new/

https://reviews.llvm.org/D73282