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The implementation assumed that compilation units did not overlap, which is not the case. The new implementation uses .debug_ranges to iterate over the requested PCs. This partially resolves #20990. The dump-cov tool is fixed but the same fix needs to be applied to `std.Build.Fuzz.WebServer` (sorting the PC list before passing it to be resolved by debug info). I am observing LLVM emit multiple 8-bit counters for the same PC addresses when enabling `-fsanitize-coverage=inline-8bit-counters`. This seems like a bug in LLVM. I can't fathom why that would be desireable.
…stEPCallback matching the default of clang's behavior. I originally put them in registerOptimizerEarlyEPCallback because I thought clang was doing that, but I see now it is behind the flag `--sanitizer-early-opt-ep` which is disabled by default.
Two fixes here: Sort by addresses after generating the line table. Debug information in the wild is not sorted and the rest of the implementation requires this data to be sorted. Handle DW.LNE.end_sequence correctly. When I originally wrote this code, I misunderstood what this opcode was supposed to do. Now I understand that it marks the *end* of an address range, meaning the current address does *not* map to the current line information. This fixes source location information for a big chunk of ReleaseSafe code.
Unfortunately, the PCs do not get sorted during linking.
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Closes #20990
The motivating example looks a lot better in ReleaseSafe mode:
But it looks worse in debug mode for some reason:
However, I verified that our LLVM IR looks good, and our debug info logic matches GDB exactly. So, I think it's two steps forward, one step back. Remaining issues are tracked by: