alok added a comment. 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'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) - If we are fine with 5% increase in size, we can enable call-site generation by default. 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