Author: David Blaikie Date: 2024-05-29T14:09:28-07:00 New Revision: bfabc958c7c0d7ddc15f23383d9da836e8c6093f
URL: https://github.com/llvm/llvm-project/commit/bfabc958c7c0d7ddc15f23383d9da836e8c6093f DIFF: https://github.com/llvm/llvm-project/commit/bfabc958c7c0d7ddc15f23383d9da836e8c6093f.diff LOG: [DebugInfo] Add flag to only emit referenced member functions (#87018) Complete C++ type information can be quite expensive - and there's limited value in representing every member function, even those that can't be called (we don't do similarly for every non-member function anyway). So add a flag to opt out of this behavior for experimenting with this more terse behavior. I think Sony already does this by default, so perhaps with a change to the defaults, Sony can migrate to this rather than a downstream patch. This breaks current debuggers in some expected ways - but those breakages are visible without this feature too. Consider member function template instantiations - they can't be consistently enumerated in every translation unit: a.h: ``` struct t1 { template <int i> static int f1() { return i; } }; namespace ns { template <int i> int f1() { return i; } } // namespace ns ``` a.cpp: ``` void f1() { t1::f1<0>(); ns::f1<0>(); } ``` b.cpp: ``` void f1(); int main() { f1(); t1::f1<1>(); ns::f1<1>(); } ``` ``` (gdb) p ns::f1<0>() $1 = 0 (gdb) p ns::f1<1>() $2 = 1 (gdb) p t1::f1<0>() Couldn't find method t1::f1<0> (gdb) p t1::f1<1>() $3 = 1 (gdb) s f1 () at a.cpp:3 3 t1::f1<0>(); (gdb) p t1::f1<0>() $4 = 0 (gdb) p t1::f1<1>() Couldn't find method t1::f1<1> (gdb) ``` (other similar non-canonical features are implicit special members (copy/move ctor/assignment operator, default ctor) and nested types (eg: pimpl idiom, where the nested type is declared-but-not-defined in one TU, and defined in another TU)) lldb can't parse the template expressions above, so I'm not sure how to test it there, but I'd guess it has similar problems. ( https://stackoverflow.com/questions/64602475/how-to-print-value-returned-by-template-member-function-in-gdb-lldb-debugging so... I guess that's just totally not supported in lldb, how unfortunate. And implicit special members are instantiated implicitly by lldb, so missing those doesn't tickle the same issue) Some very rudimentary numbers for a clang debug build: .debug_info section size: -g: 476MiB -g -fdebug-types-section: 357MiB -g -gomit-unreferenced-members: 340MiB Though it also means a major reduction in .debug_str size, -fdebug-types-section doesn't reduce string usage (so the first two examples have the same .debug_str size, 247MiB), down to 175MiB. So for total clang binary size (I don't have a quick "debug section size reduction" on-hand): 1.45 (no type units) GiB -> 1.34 -> 1.22, so it saves about 120MiB of binary size. Also open to any riffing on the flag name for sure. @probinson - would this be an accurate upstreaming of your internal handling/would you use this functionality? If it wouldn't be useful to you, it's maybe not worth adding upstream yet - not sure we'll use it at Google, but if it was useful to you folks and meant other folks could test with it it seemed maybe useful. Original Differential Revision: https://reviews.llvm.org/D152017 Added: clang/test/CodeGenCXX/debug-info-incomplete-types.cpp Modified: clang/include/clang/Basic/DebugOptions.def clang/include/clang/Driver/Options.td clang/lib/CodeGen/CGDebugInfo.cpp clang/lib/Driver/ToolChains/Clang.cpp clang/test/Driver/debug-options.c Removed: ################################################################################ diff --git a/clang/include/clang/Basic/DebugOptions.def b/clang/include/clang/Basic/DebugOptions.def index b94f6aef9ac60..bc96d5dfdf890 100644 --- a/clang/include/clang/Basic/DebugOptions.def +++ b/clang/include/clang/Basic/DebugOptions.def @@ -68,6 +68,8 @@ BENIGN_DEBUGOPT(NoInlineLineTables, 1, 0) ///< Whether debug info should contain ///< inline line tables. DEBUGOPT(DebugStrictDwarf, 1, 1) ///< Whether or not to use strict DWARF info. +DEBUGOPT(DebugOmitUnreferencedMethods, 1, 0) ///< Omit unreferenced member + ///< functions in type debug info. /// Control the Assignment Tracking debug info feature. BENIGN_ENUM_DEBUGOPT(AssignmentTrackingMode, AssignmentTrackingOpts, 2, diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td index 4119e69c85540..f64d7c60783e9 100644 --- a/clang/include/clang/Driver/Options.td +++ b/clang/include/clang/Driver/Options.td @@ -4345,6 +4345,10 @@ defm strict_dwarf : BoolOption<"g", "strict-dwarf", "the specified version, avoiding features from later versions.">, NegFlag<SetFalse>, BothFlags<[], [ClangOption, CLOption, DXCOption]>>, Group<g_flags_Group>; +defm omit_unreferenced_methods : BoolGOption<"omit-unreferenced-methods", + CodeGenOpts<"DebugOmitUnreferencedMethods">, DefaultFalse, + NegFlag<SetFalse>, + PosFlag<SetTrue, [], [CC1Option]>, BothFlags<[], [ClangOption, CLOption, DXCOption]>>; defm column_info : BoolOption<"g", "column-info", CodeGenOpts<"DebugColumnInfo">, DefaultTrue, NegFlag<SetFalse, [], [ClangOption, CC1Option]>, diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp index fac278f0e20a4..1713f7065e7a2 100644 --- a/clang/lib/CodeGen/CGDebugInfo.cpp +++ b/clang/lib/CodeGen/CGDebugInfo.cpp @@ -2836,7 +2836,7 @@ CGDebugInfo::CreateTypeDefinition(const RecordType *Ty) { // Collect data fields (including static variables and any initializers). CollectRecordFields(RD, DefUnit, EltTys, FwdDecl); - if (CXXDecl) + if (CXXDecl && !CGM.getCodeGenOpts().DebugOmitUnreferencedMethods) CollectCXXMemberFunctions(CXXDecl, DefUnit, EltTys, FwdDecl); LexicalBlockStack.pop_back(); diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp index 97e451cfe2acb..4e1c52462e584 100644 --- a/clang/lib/Driver/ToolChains/Clang.cpp +++ b/clang/lib/Driver/ToolChains/Clang.cpp @@ -45,6 +45,7 @@ #include "llvm/ADT/StringExtras.h" #include "llvm/BinaryFormat/Magic.h" #include "llvm/Config/llvm-config.h" +#include "llvm/Frontend/Debug/Options.h" #include "llvm/Object/ObjectFile.h" #include "llvm/Option/ArgList.h" #include "llvm/Support/CodeGen.h" @@ -4642,6 +4643,7 @@ renderDebugOptions(const ToolChain &TC, const Driver &D, const llvm::Triple &T, Args.addOptInFlag(CmdArgs, options::OPT_fforce_dwarf_frame, options::OPT_fno_force_dwarf_frame); + bool EnableTypeUnits = false; if (Args.hasFlag(options::OPT_fdebug_types_section, options::OPT_fno_debug_types_section, false)) { if (!(T.isOSBinFormatELF() || T.isOSBinFormatWasm())) { @@ -4652,11 +4654,24 @@ renderDebugOptions(const ToolChain &TC, const Driver &D, const llvm::Triple &T, } else if (checkDebugInfoOption( Args.getLastArg(options::OPT_fdebug_types_section), Args, D, TC)) { + EnableTypeUnits = true; CmdArgs.push_back("-mllvm"); CmdArgs.push_back("-generate-type-units"); } } + if (const Arg *A = + Args.getLastArg(options::OPT_gomit_unreferenced_methods, + options::OPT_gno_omit_unreferenced_methods)) + (void)checkDebugInfoOption(A, Args, D, TC); + if (Args.hasFlag(options::OPT_gomit_unreferenced_methods, + options::OPT_gno_omit_unreferenced_methods, false) && + (DebugInfoKind == llvm::codegenoptions::DebugInfoConstructor || + DebugInfoKind == llvm::codegenoptions::LimitedDebugInfo) && + !EnableTypeUnits) { + CmdArgs.push_back("-gomit-unreferenced-methods"); + } + // To avoid join/split of directory+filename, the integrated assembler prefers // the directory form of .file on all DWARF versions. GNU as doesn't allow the // form before DWARF v5. diff --git a/clang/test/CodeGenCXX/debug-info-incomplete-types.cpp b/clang/test/CodeGenCXX/debug-info-incomplete-types.cpp new file mode 100644 index 0000000000000..0bf59233b4e2e --- /dev/null +++ b/clang/test/CodeGenCXX/debug-info-incomplete-types.cpp @@ -0,0 +1,12 @@ +// RUN: %clang_cc1 -debug-info-kind=limited -gomit-unreferenced-methods %s -emit-llvm -o - | FileCheck %s + +struct t1 { + void f1(); + void f2(); +}; + +void t1::f1() { } + +// CHECK: distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1" +// CHECK-SAME: elements: [[ELEMENTS:![0-9]+]] +// CHECK: [[ELEMENTS]] = !{} diff --git a/clang/test/Driver/debug-options.c b/clang/test/Driver/debug-options.c index 7d061410a229f..b09238d7b6bb6 100644 --- a/clang/test/Driver/debug-options.c +++ b/clang/test/Driver/debug-options.c @@ -242,6 +242,11 @@ // RUN: %clang -### -c %s 2>&1 | FileCheck -check-prefix=NORNGBSE %s // RUN: %clang -### -c -fdebug-ranges-base-address -fno-debug-ranges-base-address %s 2>&1 | FileCheck -check-prefix=NORNGBSE %s // +// RUN: %clang -### -c -gomit-unreferenced-methods %s 2>&1 | FileCheck -check-prefix=INCTYPES %s +// RUN: %clang -### -c %s 2>&1 | FileCheck -check-prefix=NOINCTYPES %s +// RUN: %clang -### -c -gomit-unreferenced-methods -fdebug-types-section %s 2>&1 | FileCheck -check-prefix=NOINCTYPES %s +// RUN: %clang -### -c -gomit-unreferenced-methods -fstandalone-debug %s 2>&1 | FileCheck -check-prefix=NOINCTYPES %s +// // RUN: %clang -### -c -glldb %s 2>&1 | FileCheck -check-prefix=NOPUB %s // RUN: %clang -### -c -glldb -gno-pubnames %s 2>&1 | FileCheck -check-prefix=NOPUB %s // @@ -381,6 +386,9 @@ // RNGBSE: -fdebug-ranges-base-address // NORNGBSE-NOT: -fdebug-ranges-base-address // +// INCTYPES: -gomit-unreferenced-methods +// NOINCTYPES-NOT: -gomit-unreferenced-methods +// // GARANGE-DAG: -generate-arange-section // // FDTS: "-mllvm" "-generate-type-units" _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
