[PATCH] D60470: [DWARF] Prefer larger DW_AT_low_pc when constructing aranges

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

> Ah, sorry, that's not the case I was interested in. I meant a case where two object files are linked together - one has debug info, one does not. They both have a comdat function. The non-debug info version is chosen (creating the [0, X) address range in the debug info from the other object).

If the linker makes the comdat function without debug info (assuming the debug info is not in a comdat) prevailing, the one with debug info is discarded while its debug info is kept. This is essentially the same as the `--gc-sections` case.

The compile unit with 0 `DW_AT_low_pc` is actually invalid because the addresses are incorrect. It should be ignored if it overlaps with a valid range when constructing aranges. This patch will do so.

> If I understand it, this change is to the prioritization/resolution of ambiguities - but similar situations/bugs can arise when there is no ambiguity (because some code has no debug info - so it's not there to create an ambiguity). if I'm understanding/explaining correctly.

Yes, it is related to the resolution of ambiguities. The old rule is to pick the CU with the smallest `E.CUOffset`; the new rule is to pick the CU with the largest `(E.LowPC, E.CUOffset)` pair.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D60470/new/

https://reviews.llvm.org/D60470