[PATCH] Refactor debug info lexical block generation

[Paul Robinson]

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  rL LLVM

================
Comment at: lib/CodeGen/AsmPrinter/DwarfDebug.cpp:545-549
@@ +544,7 @@
+    bool Skip = Die->getAbbrev().getTag() == dwarf::DW_TAG_lexical_block;
+    for (auto &Child : Die->getChildren()) {
+      Dies.push_back(&*Child);
+      Skip &= (Child->getAbbrev().getTag() == dwarf::DW_TAG_lexical_block ||
+               Child->getAbbrev().getTag() == dwarf::DW_TAG_inlined_subroutine);
+    }
+
----------------
friss wrote:
> probinson wrote:
> > friss wrote:
> > > This seems prohibitively expensive, you are adding each and every DIE in the tree to the worklist. I'm pretty sure you could filter to only take subprograms/blocks/inline_subroutines. (Even better, don't we already collect all the functions somewhere?)
> > > 
> > > This also seems wrong. You might remove inlined_subroutines with that change and we don't want that.
> > I don't think this will remove inlined_subroutine DIEs; the intent here is that if a lexical_block contains (only) an inlined_subroutine, it's okay to eliminate the lexical_block, because the inlined_subroutine is its own scope.
> Doh, you're right. Skip is set only if the current DIE is a lexical block. Still the way this is done seems very expensive. I bet the cost of that walk in noticeable in a RelWithDebugInfo build. Can we get some numbers?
Maybe DwarfCompileUnit should keep track of the lexical blocks as they get created?  then you can just run that list here.

http://reviews.llvm.org/D9960

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