> On Aug 15, 2019, at 2:03 PM, Ismail Bennani via lldb-dev > <lldb-dev@lists.llvm.org> wrote: > > 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.
I strongly agree that unless the code can be shared, the JIT-ed DWARF expression interpreter should be kept as simple as possible and aim to support the lion's share of DWARF expressions encountered in a typical program, but making it support 100% is a lot of effort and maintenance burden with very diminishing returns. -- adrian > > 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 _______________________________________________ lldb-dev mailing list lldb-dev@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
