Author: Wolfgang Pieb Date: 2025-01-28T10:08:02Z New Revision: 71ab44a8193c56e4ef9aede4d9bac8e14760c6c6
URL: https://github.com/llvm/llvm-project/commit/71ab44a8193c56e4ef9aede4d9bac8e14760c6c6 DIFF: https://github.com/llvm/llvm-project/commit/71ab44a8193c56e4ef9aede4d9bac8e14760c6c6.diff LOG: [Clang] Add "extend lifetime" flags and release note (#110000) Following the commit that added the fake use intrinsic to LLVM, this patch adds a pair of flags for the clang frontend that emit fake use intrinsics, for the purpose of extending the lifetime of variables (either all source variables, or just the `this` pointer). This patch does not implement the fake use intrinsic emission of the flags themselves, it simply adds the flags, the corresponding release note, and the attachment of the `has_fake_uses` attribute to affected functions; the remaining functionality appears in the next patch. Co-authored-by: Stephen Tozer <stephen.to...@sony.com> Added: clang/test/Driver/extend-variable-liveness.c Modified: clang/docs/ReleaseNotes.rst clang/include/clang/Basic/CodeGenOptions.def clang/include/clang/Basic/CodeGenOptions.h clang/include/clang/Driver/Options.td clang/lib/Driver/ToolChains/Clang.cpp Removed: ################################################################################ diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index de24ab9cab5c6e..ad524ad3c5bbba 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -519,6 +519,20 @@ New Compiler Flags only for thread-local variables, and none (which corresponds to the existing ``-fno-c++-static-destructors`` flag) skips all static destructors registration. +- The ``-fextend-variable-liveness`` flag has been added to allow for improved + debugging of optimized code. Using ``-fextend-variable-liveness`` will cause + Clang to generate code that tries to preserve the liveness of source variables + through optimizations, meaning that variables will typically be visible in a + debugger more often. The flag has two levels: ``-fextend-variable-liveness``, + or ``-fextend-variable-liveness=all``, extendes the liveness of all user + variables and the ``this`` pointer. Alternatively ``-fextend-this-ptr``, or + ``-fextend-variable-liveness=this``, has the same behaviour but applies only + to the ``this`` variable in C++ class member functions, meaning its effect is + a strict subset of ``-fextend-variable-liveness``. Note that this flag + modifies the results of optimizations that Clang performs, which will result + in reduced performance in generated code; however, this feature will not + extend the liveness of some variables in cases where doing so would likely + have a severe impact on generated code performance. - The ``-Warray-compare`` warning has been added to warn about array comparison on versions older than C++20. diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def index 1ab8c7fb4d3c33..259972bdf8f001 100644 --- a/clang/include/clang/Basic/CodeGenOptions.def +++ b/clang/include/clang/Basic/CodeGenOptions.def @@ -393,6 +393,9 @@ CODEGENOPT(EnableTLSDESC, 1, 0) /// Bit size of immediate TLS offsets (0 == use the default). VALUE_CODEGENOPT(TLSSize, 8, 0) +/// The types of variables that we will extend the live ranges of. +ENUM_CODEGENOPT(ExtendVariableLiveness, ExtendVariableLivenessKind, 2, ExtendVariableLivenessKind::None) + /// The default stack protector guard offset to use. VALUE_CODEGENOPT(StackProtectorGuardOffset, 32, INT_MAX) diff --git a/clang/include/clang/Basic/CodeGenOptions.h b/clang/include/clang/Basic/CodeGenOptions.h index b64ad74d711c60..c531c656f42b7e 100644 --- a/clang/include/clang/Basic/CodeGenOptions.h +++ b/clang/include/clang/Basic/CodeGenOptions.h @@ -95,6 +95,12 @@ class CodeGenOptions : public CodeGenOptionsBase { Embed_Marker // Embed a marker as a placeholder for bitcode. }; + enum class ExtendVariableLivenessKind { + None, + This, + All, + }; + enum InlineAsmDialectKind { IAD_ATT, IAD_Intel, diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td index 75f2487143ee8b..6fa8a8273aca34 100644 --- a/clang/include/clang/Driver/Options.td +++ b/clang/include/clang/Driver/Options.td @@ -4349,6 +4349,26 @@ def stack_usage_file : Separate<["-"], "stack-usage-file">, Visibility<[CC1Option]>, HelpText<"Filename (or -) to write stack usage output to">, MarshallingInfoString<CodeGenOpts<"StackUsageOutput">>; +def fextend_variable_liveness_EQ : Joined<["-"], "fextend-variable-liveness=">, + Group<f_Group>, Visibility<[ClangOption, CC1Option]>, + HelpText<"Extend the liveness of user variables through optimizations to " + "prevent stale or optimized-out variable values when debugging. Can " + "be applied to all user variables, or just to the C++ 'this' ptr. " + "May choose not to extend the liveness of some variables, such as " + "non-scalars larger than 4 unsigned ints, or variables in any " + "inlined functions.">, + Values<"all,this,none">, + NormalizedValues<["All", "This", "None"]>, + NormalizedValuesScope<"CodeGenOptions::ExtendVariableLivenessKind">, + MarshallingInfoEnum<CodeGenOpts<"ExtendVariableLiveness">, "None">; +def fextend_this_ptr_liveness : Flag<["-"], "fextend-this-ptr-liveness">, + Visibility<[ClangOption, CC1Option]>, + Alias<fextend_variable_liveness_EQ>, AliasArgs<["this"]>, + HelpText<"Alias for -fextend-variable-liveness=this.">; +def fextend_variable_liveness : Flag<["-"], "fextend-variable-liveness">, + Visibility<[ClangOption, CC1Option]>, + Alias<fextend_variable_liveness_EQ>, AliasArgs<["all"]>, + HelpText<"Alias for -fextend-variable-liveness=all.">; defm unique_basic_block_section_names : BoolFOption<"unique-basic-block-section-names", CodeGenOpts<"UniqueBasicBlockSectionNames">, DefaultFalse, diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp index 518113e20cb063..589de953be5be1 100644 --- a/clang/lib/Driver/ToolChains/Clang.cpp +++ b/clang/lib/Driver/ToolChains/Clang.cpp @@ -7706,6 +7706,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA, if (Args.hasArg(options::OPT_fretain_comments_from_system_headers)) CmdArgs.push_back("-fretain-comments-from-system-headers"); + Args.AddLastArg(CmdArgs, options::OPT_fextend_variable_liveness_EQ); + // Forward -fcomment-block-commands to -cc1. Args.AddAllArgs(CmdArgs, options::OPT_fcomment_block_commands); // Forward -fparse-all-comments to -cc1. diff --git a/clang/test/Driver/extend-variable-liveness.c b/clang/test/Driver/extend-variable-liveness.c new file mode 100644 index 00000000000000..bdd89d6f7721ce --- /dev/null +++ b/clang/test/Driver/extend-variable-liveness.c @@ -0,0 +1,15 @@ +// Tests that -fextend-variable-liveness and its aliases are correctly passed +// by the driver. + +// RUN: %clang -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,DEFAULT +// RUN: %clang -fextend-variable-liveness=none -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,NONE +// RUN: %clang -fextend-variable-liveness=this -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,THIS +// RUN: %clang -fextend-this-ptr-liveness -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,THIS +// RUN: %clang -fextend-variable-liveness=all -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,ALL +// RUN: %clang -fextend-variable-liveness -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,ALL + +// CHECK: "-cc1" +// DEFAULT-NOT: -fextend-variable-liveness +// NONE-SAME: "-fextend-variable-liveness=none" +// THIS-SAME: "-fextend-variable-liveness=this" +// ALL-SAME: "-fextend-variable-liveness=all" _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
