[PATCH] D125693: [DebugInfo][WIP] Support types, imports and static locals declared in a lexical block (3/5)

Wed May 18 12:21:54 PDT 2022

asavonic added a comment.

Thanks a lot for the patch! It would be great to get this issue finally fixed. I assume that this is the main patch, other patches in the stack seem like just preparation/adjustments needed for this one to work.

> This an alternative implementation for D113741 <https://reviews.llvm.org/D113741> which relies on localDecls field of DISubprogram or DILexicalBlock for getting local declarations (types, imports or static variable) for a particular local scope.

Can you include a short description of the issue? PR19238 has a good and short example, we can inline it here.

> Another thing that should be noted that with this patch we will no longer emit local declarations if its parent scope doesn't have a LexicalScope calculated for it

If a local declaration (a type or a static variable) is optimized away, then with this patch we have no debug information for it, right? For types we have `-debug-info-kind=unused-types` as a workaround (as shown in lexical-block-retained-types.ll), so the issue is only with static variables that have no uses. Given that they were broken before this patch and there is no way to access them from a debugger (cannot set a breakpoint if a block is optimized away), I think it is fine.

================
Comment at: llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1382
+      assert((!GV->getScope() || !isa<DILocalScope>(GV->getScope())) &&
+             "Unexpected function-local declaration!");
       if (Processed.insert(GV).second)
----------------
So here we discard LLVM IR metadata that have local declarations tied to a CU, right? This will break compatibility with old LLVM IR. Can we do some upgrade to convert this "old style" metadata the way we expect it now? Does it make sense to support both variants?

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https://reviews.llvm.org/D125693