[PATCH] D69027: [llvm-dwarfdump][Statistics] Fix calculation of OffsetToFirstDefinition

Fri Nov 1 04:10:25 PDT 2019

krisb added a comment.

Currently (in the current master), we have the following statistics related to the discussion:

1. The total number of bytes covered by DW_AT_location over all variables. We also have separate statistics for local vars only, params only and entry values for vars and params.
2. The total number of bytes in variable's scopes over all variables. Variable's scope means a scope adjusted to the lowerest address in variables' DW_AT_location. Plus, separate statistics for local vars only and params only.
3. The number of variables in each coverage bucket, where the coverage bucket calculated as 'the number of bytes covered by a variable's DW_AT_location' / 'the number of bytes in variable's enclosing scope'. Variable's enclosing scope means a full scope (e.g. full subprogram, lexical block, etc.) without any adjustments. There are also separate statistics for local vars and params, and all the three where entry values are excluded.

I propose to move to the following:

1. Keep as is.
2. Keep but:
  - document properly with all the assumption and limitations, as 'it's known that the adjusted scope might not accurately represent variable's scope, but we still find it useful',
  - do not calculate it for params,
  - apply fixes proposed in this patch (i.e. account non-contiguous ranges while calculating OffsetToFirstDefinition).
  - TODO: there might be a field for further investigation that can improve the heuristic.
3. Keep but:
  - switch to 'the number of bytes covered by a variable's DW_AT_location' / 'the number of bytes in variable's adjusted scope' for local vars,
  - document everything related to the 'adjusted' scope.
4. Add new statistics: the total number of bytes in variable's enclosing scopes over all variables.

What do you think?

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69027/new/

https://reviews.llvm.org/D69027