dblaikie added a comment. In D99160#2698980 <https://reviews.llvm.org/D99160#2698980>, @alok wrote:
> In D99160#2671899 <https://reviews.llvm.org/D99160#2671899>, @dblaikie wrote: > >> In D99160#2670460 <https://reviews.llvm.org/D99160#2670460>, @djtodoro wrote: >> >>> In D99160#2669576 <https://reviews.llvm.org/D99160#2669576>, @dblaikie >>> wrote: >>> >>>> In D99160#2668977 <https://reviews.llvm.org/D99160#2668977>, @djtodoro >>>> wrote: >>>> >>>>> I think that the Debug Entry Values feature should not be enabled by >>>>> default for non optimized code, so the >>>>> `TargetOptions::ShouldEmitDebugEntryValues()` should be patched with >>>>> checking of optimization level (it should be > 0). >>>> >>>> That's currently intended to be already handled by the frontend, right? >>>> (clang only sets `EnableDebugEntryValues` (which >>>> `ShouldEmitDebugEntryValues` checks (hmm, it checks under 'or', not 'and', >>>> so I'm not sure where the "only above -O0" is implemented, but it is >>>> implemented somewhere?) if optimizations are enabled, yeah?) >>>> >>>> Oh, is entry_values actually not conditionalized? It's only the call_site >>>> support that's currently conditionalized on "above -O0"? >>> >>> Looks like there is no explicit check of optimization level (above "-O0"), >>> neither on frontend nor backend for entry-values generation. I think it is >>> the situation since there should not be any optimization (at least that I >>> am aware of, in the case of C/C++) that would cause the entry-values >>> generation... >>> >>>> Hmm - If that's the case, and we currently have some cases where >>>> entry_values are emitted at -O0, I'm not sure /not/ emitting those is the >>>> right call either. If we believe/have data to show that there are so few >>>> useful uses of entry_value at -O0 that it's not worth the DWARF size >>>> growth to put call_sites in at -O0, then I think it might still be worth >>>> leaving the entry_values in (unless they take up a bunch of extra space) >>>> for the cases of mixed optimization compilation (-O0 some code you're >>>> debugging, but building the rest with optimizations). >>> >>> Yeah... That is valuable example... I am thinking in that direction as >>> well, and I am closer to the enabling it for -O0 case if that is useful >>> (and there is no dramatic cost in terms of DWARF size). >> >> Does anyone have this example (where DW_OP_entry_value is used at -O0)? It'd >> be great to look at it & see if it's a case of unnecessarily losing the >> location, or legitimately losing it and using entry_value for best-effort >> recovery (& then a question of whether the loss is appropriate at -O0, or if >> we want to pessimize -O0 further to avoid the loss). I think this ^ still needs understanding/investigation. Do you have an example with OP_entry_value at -O0? >> I'd worry about turning on call_sites at -O0 - there'd be a lot more calls >> (especially for C++ code with lots of implicit operations), but numbers will >> be needed in any case, so not worth much speculation. > > Sorry for late response. > I tried building > https://github.com/flang-compiler/classic-flang-llvm-project.git (branch > release_11x) with compiler (current patch (https://reviews.llvm.org/D99160) > and https://reviews.llvm.org/D99238) with -O0 -g . > Interestingly there was no difference. > Reason: https://reviews.llvm.org/D99238 is not sufficient for clang/clang++ > to enable call-site generation with FastISel though it is sufficient for > Flang compiler. > Below additional patch is needed to generate call-sites > > ````````````````````````````````````` > > diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp > b/clang/lib/CodeGen/CGDebugInfo.cpp > index a77f52bd235b..8d4e11faa018 100644 > > - a/clang/lib/CodeGen/CGDebugInfo.cpp > > +++ b/clang/lib/CodeGen/CGDebugInfo.cpp > @@ -5149,9 +5149,9 @@ llvm::DebugLoc > CGDebugInfo::SourceLocToDebugLoc(SourceLocation Loc) { > } > > llvm::DINode::DIFlags CGDebugInfo::getCallSiteRelatedAttrs() const { > > - // Call site-related attributes are only useful in optimized programs, and > - // when there's a possibility of debugging backtraces. > - if (!CGM.getLangOpts().Optimize || DebugKind == codegenoptions::NoDebugInfo > || > > + // Call site-related attributes are useful when there's a possibility of > + // debugging backtraces. > + if (DebugKind == codegenoptions::NoDebugInfo || > > DebugKind == codegenoptions::LocTrackingOnly) > return llvm::DINode::FlagZero; > > ````````````````````````````````````` > > With this patch Clang/Clang++ turn on LLVM IR flag "DIFlagAllCallsDescribed", > in absence of this LLVM does not generate call-site. > > With the above patch applied below is the comparison of sizes of shared > libraries. > > Name of shared library - Size (without callsite) - Size (with callsites) - % > incresase in size > > > ``````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` > > PipSqueak.so 73192 75048 2% > SecondLib.so 73192 75048 2% > TestPlugin.so 1694024 1700704 0% > libLLVMDlltoolDriver.so 336568 347872 3% > libLLVMDebugInfoPDB.so 14463832 15360784 6% > libLLVMOrcError.so 108880 111184 2% > libLLVMTarget.so 2645104 2677448 1% > libLLVMFrontendOpenMP.so 2354728 2505232 6% > libLLVMProfileData.so 7901688 8373632 5% > libLLVMOrcJIT.so 28838432 30490640 5% > libLLVMRemarks.so 3311680 3551856 7% > libgtest.so 2374120 2523112 6% > libLLVMDemangle.so 1350616 1490832 10% > libLLVMAsmParser.so 6961216 7366040 5% > LLVMHello.so 394624 396120 0% > libLLVMGlobalISel.so 18886648 19698008 4% > libLLVMDebugInfoMSF.so 1288376 1365040 5% > libLLVMCoverage.so 4225224 4502104 6% > libLLVMFuzzMutate.so 3859968 3973808 2% > libRemarks.so 6696 6696 0% > libLLVMDebugInfoDWARF.so 11914848 12750784 7% > libLLVMMCParser.so 6419464 6873000 7% > libLLVMTableGen.so 4855536 5180760 6% > libLLVMDWARFLinker.so 5407528 5628576 4% > Bye.so 1858848 1872672 0% > libLLVMMCJIT.so 1470952 1526544 3% > libLLVMMC.so 16931504 17741376 4% > libLLVMipo.so 43554712 46019392 5% > libLLVMLineEditor.so 208216 216360 3% > libbenchmark_main.so 18904 19408 2% > libbenchmark.so 3308304 3507632 6% > libLTO.so 2240720 2277408 1% > libLLVMInterpreter.so 2614696 2749128 5% > libLLVMTransformUtils.so 47925248 50476512 5% > libLLVMX86Desc.so 8047928 8213152 2% > libLLVMCoroutines.so 6478080 6766880 4% > libLLVMJITLink.so 5590936 6066736 8% > libLLVMVectorize.so 19557808 20665544 5% > libLLVMX86Disassembler.so 2820056 2849376 1% > libLLVMBitReader.so 8282648 8823240 6% > libLLVMMCA.so 3242016 3405624 5% > libLLVMBitWriter.so 6544032 6867976 4% > libLLVMMIRParser.so 5739688 5980104 4% > libLLVMLTO.so 13272272 13786192 3% > libLLVMCore.so 46109224 48840008 5% > libLLVMBitstreamReader.so 561896 600624 6% > libLLVMObjectYAML.so 23110160 24648160 6% > libLLVMSupport.so 20349728 21953112 7% > libLLVMIRReader.so 1215672 1237960 1% > libLLVMX86Info.so 76488 76624 0% > libLLVMSelectionDAG.so 34358968 36876128 7% > libLLVMExecutionEngine.so 2962160 3073224 3% > libLLVMSymbolize.so 1980760 2089728 5% > libLLVMPasses.so 18574960 19459712 4% > libLLVMOption.so 869784 920976 5% > libLLVMObject.so 15138656 16383168 8% > libLLVMTextAPI.so 3191272 3384560 6% > libLLVMX86CodeGen.so 55202744 58068088 5% > libLLVMAggressiveInstCombine.so 2354936 2419048 2% > libLLVMExtensions.so 23904 23904 0% > libLLVMWindowsManifest.so 351608 370168 5% > libLLVMObjCARCOpts.so 4964488 5150120 3% > libLLVMBinaryFormat.so 1325752 1431448 7% > libLLVMDebugInfoGSYM.so 2909272 3094616 6% > libLLVMTestingSupport.so 623608 656640 5% > libgtest_main.so 42856 43608 1% > libLLVMLinker.so 3070264 3210248 4% > libLLVMCFGuard.so 1082488 1096104 1% > libLLVMCodeGen.so 139859816 146452160 4% > libLLVMDebugInfoCodeView.so 7742896 8497704 9% > libLLVMX86AsmParser.so 2590816 2714008 4% > libLLVMRuntimeDyld.so 6592016 7094048 7% > libLLVMInstCombine.so 18194728 19705184 8% > BugpointPasses.so 780112 788304 1% > libLLVMScalarOpts.so 73110536 77534912 6% > libLLVMXRay.so 3993696 4251280 6% > libLLVMMCDisassembler.so 1292912 1313536 1% > libLLVMFrontendOpenACC.so 96008 102656 6% > libLLVMInstrumentation.so 21038808 22351384 6% > libLLVMLibDriver.so 1595936 1638704 2% > libLLVMAsmPrinter.so 25818000 26842816 3% > libLLVMAnalysis.so 79615056 83995856 5% > > ````````````````````````````````````````````````````````````````````` > > sum 79615057 83995857 5% > > So the conclusion is, > > - We have a Flag which can help us if we want to enable callsite generation > selectively (only for Flang) It doesn't seem to me, so far, like this is a place where Flang and Clang should diverge - they're both doing the same sort of thing for the same reasons/likely with the same sort of tradeoffs of location accuracy V size cost. > - If we are fine with 5% increase in size, we can enable call-site generation > by default. I'd actually be somewhat more worried about object size, rather than/in addition to executable size, due to the increase in relocations (especially with DWARFv5 (& especially with the `-mllvm -minimize-addr-in-v5=Ranges` which further reduces debug_addr, but can't handle labels and call sites (unlike `-minimize-addr-in-v5=Expressions` or `-minimize-addr-in-v5=Form`)), which does a lot to reduce the number of relocations by using debug_addr and address sharing on debug_rnglists/loclists/etc) which can't be compressed, etc. CHANGES SINCE LAST ACTION https://reviews.llvm.org/D99160/new/ https://reviews.llvm.org/D99160 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits