I built Clang (and LLVM) in Release Mode with Debug Info (-O2), and got these results:
| Dwarf Occurences | Occurences | |----------------------|-----------------| | DW\_OP\_deref | 1,570 | | DW\_OP\_const | 3,791 | | DW\_OP\_addr | 9,528 | | DW\_OP\_lit | 62,826 | | DW\_OP\_fbreg | 205,382 | | DW\_OP\_piece | 242,888 | | DW\_OP\_stack\_value | 992,261 | | DW\_OP\_breg | 1,006,070 | | DW\_OP\_reg | 5,175,831 | | **Total** | **7,700,147** | I could technically implement the logic to support DW_OP_reg, DW_OP_breg and DW_OP_stack_value fairly easily (which still represents 90% of all ops). However, DW_OP_piece is a more complex operation since it combines several other operations, and would require more work. This would also imply that there will 2 DWARF Expression Interpreter in LLDB, hence twice as much code to maintain … I’ll try to see if I can use the existing interpreter for this feature. Ismail > On Aug 14, 2019, at 3:42 PM, Finkel, Hal J. <hfin...@anl.gov> wrote: > > > On 8/14/19 3:52 PM, Ismail Bennani via lldb-dev wrote: >> Hi everyone, >> >> I’m Ismail, a compiler engineer intern at Apple. As a part of my internship, >> I'm adding Fast Conditional Breakpoints to LLDB, using code patching. >> >> ... >> >> Since all the registers are already mapped to a structure, I should >> be able to support more __DWARF Operations__ in the future. >> >> After collecting some metrics on the __Clang__ binary, built at __-O0__, >> the debug info shows that __99%__ of the most used DWARF Operations are : >> >> |DWARF Operation| Occurrences | >> |---------------|---------------------------| >> |DW\_OP_fbreg | 2 114 612 | >> |DW\_OP_reg | 820 548 | >> |DW\_OP_constu | 267 450 | >> |DW\_OP_addr | 17 370 | >> >> | __Top 4__ | __3 219 980 Occurrences__ | >> |---------------|---------------------------| >> | __Total__ | __3 236 859 Occurrences__ | >> >> Those 4 operations are the one that I'll support for now. >> To support more complex expressions, we would need to JIT-compile >> a DWARF expression interpreter. > > > First, this all sounds really useful. > > Out of curiosity, how do these statistics change if you compile Clang > with -O1? Many of my users need to debug slightly-optimized code. > > -Hal > > > -- > Hal Finkel > Lead, Compiler Technology and Programming Languages > Leadership Computing Facility > Argonne National Laboratory > _______________________________________________ lldb-dev mailing list lldb-dev@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
