[profile] Add a clang option -fprofile-continuous that enables continuous instrumentation profiling mode (#124353)

In Continuous instrumentation profiling mode, profile or coverage data
collected via compiler instrumentation is continuously synced to the
profile file. This feature has existed for a while, and is documented
here:

https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#running-the-instrumented-program
This PR creates a user facing option to enable the feature.

---------

Co-authored-by: Wael Yehia <[email protected]>

Author: w2yehia

clang/docs/UsersManual.rst

@@ -3125,6 +3125,24 @@ indexed format, regardeless whether it is produced by frontend or the IR pass.
   overhead. ``prefer-atomic`` will be transformed to ``atomic`` when supported
   by the target, or ``single`` otherwise.
 
+.. option:: -fprofile-continuous
+
+  Enables the continuous instrumentation profiling where profile counter updates
+  are continuously synced to a file. This option sets any neccessary modifiers
+  (currently ``%c``) in the default profile filename and passes any necessary
+  flags to the middle-end to support this mode. Value profiling is not supported
+  in continuous mode.
+
+  .. code-block:: console
+
+    $ clang++ -O2 -fprofile-generate -fprofile-continuous code.cc -o code
+
+  Running ``./code`` will collect the profile and write it to the
+  ``default_xxxx.profraw`` file. However, if ``./code`` abruptly terminates or
+  does not call ``exit()``, in continuous mode the profile collected up to the
+  point of termination will be available in ``default_xxxx.profraw`` while in
+  the non-continuous mode, no profile file is generated.
+
 .. option:: -ftemporal-profile
 
   Enables the temporal profiling extension for IRPGO to improve startup time by

clang/include/clang/Basic/CodeGenOptions.def

@@ -221,6 +221,7 @@ AFFECTING_VALUE_CODEGENOPT(OptimizationLevel, 2, 0) ///< The -O[0-3] option spec
 AFFECTING_VALUE_CODEGENOPT(OptimizeSize, 2, 0) ///< If -Os (==1) or -Oz (==2) is specified.
 
 CODEGENOPT(AtomicProfileUpdate , 1, 0) ///< Set -fprofile-update=atomic
+CODEGENOPT(ContinuousProfileSync, 1, 0) ///< Enable continuous instrumentation profiling
 /// Choose profile instrumenation kind or no instrumentation.
 ENUM_CODEGENOPT(ProfileInstr, ProfileInstrKind, 2, ProfileNone)
 /// Choose profile kind for PGO use compilation.

clang/include/clang/Driver/Options.td

@@ -1795,6 +1795,11 @@ def fprofile_update_EQ : Joined<["-"], "fprofile-update=">,
     Values<"atomic,prefer-atomic,single">,
     MetaVarName<"<method>">, HelpText<"Set update method of profile counters">,
     MarshallingInfoFlag<CodeGenOpts<"AtomicProfileUpdate">>;
+def fprofile_continuous : Flag<["-"], "fprofile-continuous">,
+    Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
+    HelpText<"Enable continuous instrumentation profiling mode">,
+    MarshallingInfoFlag<CodeGenOpts<"ContinuousProfileSync">>;
+
 defm pseudo_probe_for_profiling : BoolFOption<"pseudo-probe-for-profiling",
   CodeGenOpts<"PseudoProbeForProfiling">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption], "Emit">,

clang/lib/CodeGen/BackendUtil.cpp

@@ -124,15 +124,25 @@ namespace clang {
 extern llvm::cl::opt<bool> ClSanitizeGuardChecks;
 }
 
-namespace {
-
 // Default filename used for profile generation.
-std::string getDefaultProfileGenName() {
+static std::string getDefaultProfileGenName() {
   return DebugInfoCorrelate || ProfileCorrelate != InstrProfCorrelator::NONE
              ? "default_%m.proflite"
              : "default_%m.profraw";
 }
 
+// Path and name of file used for profile generation
+static std::string getProfileGenName(const CodeGenOptions &CodeGenOpts) {
+  std::string FileName = CodeGenOpts.InstrProfileOutput.empty()
+                             ? getDefaultProfileGenName()
+                             : CodeGenOpts.InstrProfileOutput;
+  if (CodeGenOpts.ContinuousProfileSync)
+    FileName = "%c" + FileName;
+  return FileName;
+}
+
+namespace {
+
 class EmitAssemblyHelper {
   CompilerInstance &CI;
   DiagnosticsEngine &Diags;
@@ -551,7 +561,9 @@ getInstrProfOptions(const CodeGenOptions &CodeGenOpts,
     return std::nullopt;
   InstrProfOptions Options;
   Options.NoRedZone = CodeGenOpts.DisableRedZone;
-  Options.InstrProfileOutput = CodeGenOpts.InstrProfileOutput;
+  Options.InstrProfileOutput = CodeGenOpts.ContinuousProfileSync
+                                   ? ("%c" + CodeGenOpts.InstrProfileOutput)
+                                   : CodeGenOpts.InstrProfileOutput;
   Options.Atomic = CodeGenOpts.AtomicProfileUpdate;
   return Options;
 }
@@ -822,13 +834,12 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
 
   if (CodeGenOpts.hasProfileIRInstr())
     // -fprofile-generate.
-    PGOOpt = PGOOptions(
-        CodeGenOpts.InstrProfileOutput.empty() ? getDefaultProfileGenName()
-                                               : CodeGenOpts.InstrProfileOutput,
-        "", "", CodeGenOpts.MemoryProfileUsePath, nullptr, PGOOptions::IRInstr,
-        PGOOptions::NoCSAction, ClPGOColdFuncAttr,
-        CodeGenOpts.DebugInfoForProfiling,
-        /*PseudoProbeForProfiling=*/false, CodeGenOpts.AtomicProfileUpdate);
+    PGOOpt = PGOOptions(getProfileGenName(CodeGenOpts), "", "",
+                        CodeGenOpts.MemoryProfileUsePath, nullptr,
+                        PGOOptions::IRInstr, PGOOptions::NoCSAction,
+                        ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling,
+                        /*PseudoProbeForProfiling=*/false,
+                        CodeGenOpts.AtomicProfileUpdate);
   else if (CodeGenOpts.hasProfileIRUse()) {
     // -fprofile-use.
     auto CSAction = CodeGenOpts.hasProfileCSIRUse() ? PGOOptions::CSIRUse
@@ -872,18 +883,13 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
              PGOOpt->Action != PGOOptions::SampleUse &&
              "Cannot run CSProfileGen pass with ProfileGen or SampleUse "
              " pass");
-      PGOOpt->CSProfileGenFile = CodeGenOpts.InstrProfileOutput.empty()
-                                     ? getDefaultProfileGenName()
-                                     : CodeGenOpts.InstrProfileOutput;
+      PGOOpt->CSProfileGenFile = getProfileGenName(CodeGenOpts);
       PGOOpt->CSAction = PGOOptions::CSIRInstr;
     } else
-      PGOOpt = PGOOptions("",
-                          CodeGenOpts.InstrProfileOutput.empty()
-                              ? getDefaultProfileGenName()
-                              : CodeGenOpts.InstrProfileOutput,
-                          "", /*MemoryProfile=*/"", nullptr,
-                          PGOOptions::NoAction, PGOOptions::CSIRInstr,
-                          ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling);
+      PGOOpt = PGOOptions("", getProfileGenName(CodeGenOpts), "",
+                          /*MemoryProfile=*/"", nullptr, PGOOptions::NoAction,
+                          PGOOptions::CSIRInstr, ClPGOColdFuncAttr,
+                          CodeGenOpts.DebugInfoForProfiling);
   }
   if (TM)
     TM->setPGOOption(PGOOpt);

clang/lib/Driver/ToolChains/Clang.cpp

@@ -580,6 +580,7 @@ static void addPGOAndCoverageFlags(const ToolChain &TC, Compilation &C,
                                    const ArgList &Args, SanitizerArgs &SanArgs,
                                    ArgStringList &CmdArgs) {
   const Driver &D = TC.getDriver();
+  const llvm::Triple &T = TC.getTriple();
   auto *PGOGenerateArg = Args.getLastArg(options::OPT_fprofile_generate,
                                          options::OPT_fprofile_generate_EQ,
                                          options::OPT_fno_profile_generate);
@@ -785,6 +786,34 @@ static void addPGOAndCoverageFlags(const ToolChain &TC, Compilation &C,
       D.Diag(diag::err_drv_unsupported_option_argument)
           << A->getSpelling() << Val;
   }
+  if (const auto *A = Args.getLastArg(options::OPT_fprofile_continuous)) {
+    if (!PGOGenerateArg && !CSPGOGenerateArg && !ProfileGenerateArg)
+      D.Diag(clang::diag::err_drv_argument_only_allowed_with)
+          << A->getSpelling()
+          << "-fprofile-generate, -fprofile-instr-generate, or "
+             "-fcs-profile-generate";
+    else {
+      CmdArgs.push_back("-fprofile-continuous");
+      // Platforms that require a bias variable:
+      if (T.isOSBinFormatELF() || T.isOSAIX()) {
+        CmdArgs.push_back("-mllvm");
+        CmdArgs.push_back("-runtime-counter-relocation");
+      }
+      // -fprofile-instr-generate does not decide the profile file name in the
+      // FE, and so it does not define the filename symbol
+      // (__llvm_profile_filename). Instead, the runtime uses the name
+      // "default.profraw" for the profile file. When continuous mode is ON, we
+      // will create the filename symbol so that we can insert the "%c"
+      // modifier.
+      if (ProfileGenerateArg &&
+          (ProfileGenerateArg->getOption().matches(
+               options::OPT_fprofile_instr_generate) ||
+           (ProfileGenerateArg->getOption().matches(
+                options::OPT_fprofile_instr_generate_EQ) &&
+            strlen(ProfileGenerateArg->getValue()) == 0)))
+        CmdArgs.push_back("-fprofile-instrument-path=default.profraw");
+    }
+  }
 
   int FunctionGroups = 1;
   int SelectedFunctionGroup = 0;

clang/test/CodeGen/profile-continuous.c

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -emit-llvm -fprofile-instrument=llvm -fprofile-continuous %s -o - | FileCheck %s --check-prefix=IRPGO
+// RUN: %clang_cc1 -emit-llvm -fprofile-instrument=llvm -fprofile-continuous -fprofile-instrument-path=mydir/default_%m.profraw -mllvm -runtime-counter-relocation %s -o - \
+// RUN:  | FileCheck %s --check-prefix=IRPGO_EQ
+// RUN: %clang_cc1 -emit-llvm -O2 -fprofile-instrument=csllvm -fprofile-continuous %s -o - | FileCheck %s --check-prefix=CSIRPGO
+// RUN: %clang_cc1 -emit-llvm -fprofile-instrument=clang -fprofile-continuous -fprofile-instrument-path=default.profraw %s -o - | FileCheck %s --check-prefix=CLANG_PGO
+
+// IRPGO: @__llvm_profile_filename = {{.*}} c"%cdefault_%m.profraw\00"
+// IRPGO_EQ: @__llvm_profile_filename = {{.*}} c"%cmydir/default_%m.profraw\00"
+// CSIRPGO: @__llvm_profile_filename = {{.*}} c"%cdefault_%m.profraw\00"
+// CLANG_PGO: @__llvm_profile_filename = {{.*}} c"%cdefault.profraw\00"
+void foo(){}

clang/test/Driver/fprofile-continuous.c

@@ -0,0 +1,21 @@
+// 1) test on platforms that (do or do not) require runtime relocation
+
+// RUN: %clang --target=x86_64-darwin -fprofile-generate -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=NO_RELOC
+// NO_RELOC: "-cc1" {{.*}} "-fprofile-continuous"
+// NO_RELOC-NOT: "-mllvm" "-runtime-counter-relocation"
+
+// RUN: %clang --target=powerpc64-ibm-aix -fprofile-generate -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=RELOC
+// RUN: %clang --target=x86_64-unknown-fuchsia -fprofile-generate -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=RELOC
+// RELOC: "-cc1" {{.*}} "-fprofile-continuous" "-mllvm" "-runtime-counter-relocation"
+
+// 2) test -fprofile-continuous with cs-profile-generate and -fprofile-instr-generate
+
+// RUN: %clang --target=powerpc-ibm-aix -fprofile-instr-generate -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=CLANG_PGO
+// RUN: %clang --target=powerpc64le-unknown-linux -fprofile-instr-generate= -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=CLANG_PGO
+// CLANG_PGO: "-cc1" {{.*}} "-fprofile-continuous" "-mllvm" "-runtime-counter-relocation" "-fprofile-instrument-path=default.profraw"
+
+// RUN: %clang --target=x86_64-unknown-fuchsia -fcs-profile-generate -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=RELOC
+
+// RUN: not %clang -fprofile-continuous -### -c %s 2>&1 | FileCheck %s --check-prefix=ERROR
+// ERROR: error: invalid argument '-fprofile-continuous' only allowed with '-fprofile-generate, -fprofile-instr-generate, or -fcs-profile-generate'
+void foo(){}