Forwarding to lldb-dev now that I’ve signed up. From: llvm-dev <llvm-dev-boun...@lists.llvm.org> On Behalf Of Cazalet-Hyams, Orlando via llvm-dev Sent: 24 September 2020 08:54 To: Robinson, Paul <paul.robin...@sony.com>; Eric Christopher <echri...@gmail.com>; LLDB Dev <lldb-dev@lists.llvm.org>; 'llvm-...@lists.llvm.org' <llvm-...@lists.llvm.org> Subject: Re: [llvm-dev] Optimised-code debugging experience Round Table
Hi Paul, Eric, lists, FWIW I agree with Paul here. Given the limited time available for the discussions I think it makes sense to split up the conversations to keep them focused. Though, it'd be good to coordinate non-overlapping time slots. As you say, it is likely that people (including me) would want to attend more than one of these. Saying that, I've only had 3 people outside of Sony express an interest in the Round Table that I proposed. At this rate we may not have the requisite numbers to split. Of course, if that number is indicative of actual turn out then we won't need to split anyway, but I suspect that there will be more attendees on the day. We must also remember that the Round Table submission deadline is tomorrow (tonight?). Unless more people express an interest very soon, I think we might need to fall back onto the single Round Table. Thanks, Orlando From: Robinson, Paul <paul.robin...@sony.com<mailto:paul.robin...@sony.com>> Sent: 23 September 2020 15:21 To: Eric Christopher <echri...@gmail.com<mailto:echri...@gmail.com>>; Cazalet-Hyams, Orlando <orlando.hy...@sony.com<mailto:orlando.hy...@sony.com>>; LLDB Dev <lldb-dev@lists.llvm.org<mailto:lldb-dev@lists.llvm.org>>; 'llvm-...@lists.llvm.org' <llvm-...@lists.llvm.org<mailto:llvm-...@lists.llvm.org>> Subject: RE: [llvm-dev] Optimised-code debugging experience Round Table Hi Eric & Orlando, It’s great to see interest in a lot of different aspects of debug info. At the same time, I’m concerned about a risk to making the topic so broad that we don’t have time to get through all the things people want to get through. I’m thinking there’s a different way to slice the topics, hopefully without much overlap, but that will allow a bit more focus. No doubt a lot of the same people would be interested in multiple slices, but by limiting the scope of each conversation I’m hoping we’ll get more accomplished. I daresay a lot of people interested in debug-info quality in general might totally tune out a DWARF-nerd discussion 😊 The slicing could be something like this: 1. Getting LLVM to do a better job of tracking info internally, so what gets emitted in the end is more representative of the original program. This should improve the debugging experience by letting the debugger do a better job of mapping the executing program to the original source, because the data it works with is more accurate/complete. * This is basically about IR/Metadata handling and representation, although it might leak into things like the “is_stmt” flag, and doing better with “prologue_end,” which are currently handled by AsmPrinter. * Better handling of induction variables, entry-values, variables with multiple locations, etc. 2. Changes to optimization passes/pipelines and codegen, to avoid borking the source-location and value/variable tracking; again this should improve the debugging experience by letting the debugger do a better job of mapping the executing program back to the original source, because that mapping is simpler. * This is basically about IR/MIR transforms, and is where an Og/O1 kind of topic would fit. * Also things like extended lifetimes, limiting code motion/duplication, etc. 3. Changing the DWARF spec itself to improve the completeness and efficiency of the information it contains. This should improve the debugging experience by making the DWARF itself a richer information source, to the extent that it can describe more of what happened to the original program; also hopefully any efficiency improvements will allow the debugger to be more responsive. * This is obviously about DWARF itself, although to some extent how we go about generating it. * Take better advantage of ranges and the .debug_addr table. dblaikie and clayborg have put up ideas about this. * Figure out a way to allow tracking multiple source locations for an individual instruction. Right now we mostly give up and set locations to line-0 when this happens. * Understand the competing needs of profiling and debugging consumers, and see what might be doable there. (Although this might be tough enough to be its own topic.) 4. Debug-info testing/validation. How do we decide what is “correct”? * What are the tools we have, what are they good/bad at, what’s missing? I hear that round-tables can be proposed for either ~half hour or ~full hour, so with more focused topics we might rather have shorter sessions? Thanks, --paulr From: llvm-dev <llvm-dev-boun...@lists.llvm.org<mailto:llvm-dev-boun...@lists.llvm.org>> On Behalf Of Eric Christopher via llvm-dev Sent: Tuesday, September 22, 2020 2:42 PM To: Cazalet-Hyams, Orlando <orlando.hy...@sony.com<mailto:orlando.hy...@sony.com>>; LLDB Dev <lldb-dev@lists.llvm.org<mailto:lldb-dev@lists.llvm.org>> Cc: llvm-...@lists.llvm.org<mailto:llvm-...@lists.llvm.org> Subject: Re: [llvm-dev] Optimised-code debugging experience Round Table +LLDB Dev<mailto:lldb-dev@lists.llvm.org> I'll sign up. :) My particular interests are: - Og (and O1 as Og) - Correctness testing tools Past that the rest of your list seems quite specific, but the overall "line tables" and "variable locations" are important. Relatedly we have a number of DWARF committee members in llvm and another possible discussion area could be: "what extensions do debug info consumers think should happen to make dwarf a better input into debugging". Thanks. -eric On Tue, Sep 22, 2020 at 8:43 AM Cazalet-Hyams, Orlando via llvm-dev <llvm-...@lists.llvm.org<mailto:llvm-...@lists.llvm.org>> wrote: Hi all, I haven't seen a proposal for an optimised-code debugging experience Round Table yet so here goes! Please let me know if you are interested by emailing me at: orlando.hy...@sony.com<mailto:orlando.hy...@sony.com> Below is a non-exhaustive list of possible topics. Feel free to include any preferences and suggestions in your response. a. Line tables: 1. Can we fix is_stmt? 2. Is prologue_end reliable? 3. General stepping behaviour/quality. b. Variable locations: 1. The state of DW_OP_entry_values in llvm. 2. The state of the instruction-referencing DBG_VALUE work. 3. The state of multi-register DWARF expressions in llvm. 4. The possibility of salvaging out-of-liveness values using the 3 projects mentioned above. 5. Floating point debug-info quality in llvm. 6. Loop induction variable locations. c. Testing debug-info: 1. Variable correctness testing tools. 2. Location coverage testing tools. d. The state of -Og. Please respond before Friday (25th) if you are interested as that is the submission deadline. Thanks, Orlando _______________________________________________ LLVM Developers mailing list llvm-...@lists.llvm.org<mailto:llvm-...@lists.llvm.org> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<https://urldefense.com/v3/__https:/lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev__;!!JmoZiZGBv3RvKRSx!qZNIykNGKyisLnvZ4ZEA_BQPbabOTQucziiEgm1DmJ154Z_DBQc8k6R5JENTM2Ewyg$>
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