[PATCH] D74169: [WIP][LLD][ELF][DebugInfo] Remove obsolete debug info.

[Greg Clayton via Phabricator via llvm-commits]

clayborg added a comment.

In D74169#1960551 <https://reviews.llvm.org/D74169#1960551>, @dblaikie wrote:

> In D74169#1960503 <https://reviews.llvm.org/D74169#1960503>, @clayborg wrote:
>
> > Nice! Another thing I have been seeing a lot of is when functions are coalesced and many .o files have the same function that gets linked to the same location. We end up with many duplicate DWARF DIEs in the final executable since the linker will just link all of the DWARF for each function over and over (.debug_info and .debug_line content). I found this when making GSYM files from the DWARF and noticing that I had hundreds of duplicate entries that matched exactly. This would be a great follow up patch for --gc-debuginfo
>
>
> Given this is built on top of the DWARFLinker used for llvm-dsymutil which, I believe, already strips out those duplicate descriptions - hopefully that's already included in the functionality under review? But good to check/ask - @avl does this patch already do the good things for duplicate (or dropped) function sections?
>
> (eg: "inline void f1() { } void f2() { f1(); }" + "inline void f1() { } void f2(); int main() { f1(); f2(); }" compiled and linked at -O0 the DWARF would usually contain two descriptions of 'f1', but ideally with a DWARF aware linker it'd contain only one description of 'f1'. Similarly: "void f1() { } void f2() { }" + "void f2(); int main() { f2(); }" compiled and linked with -ffunction-sections -Wl,-gc-sections would normally contain a DWARF description of "f1" but no code for f1, and a DWARF aware linker would strip out the DWARF description of 'f1' here)


dsymutil's ODR does unique the types and only emit one copy. See my comment on implicit methods as one thing that can cause multiple copies of a type to be emitted.


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