Add -fprofile-update={atomic,prefer-atomic,single}

GCC 7 introduced -fprofile-update={atomic,prefer-atomic} (prefer-atomic is for
best efforts (some targets do not support atomics)) to increment counters
atomically, which is exactly what we have done with -fprofile-instr-generate
(D50867) and -fprofile-arcs (b5ef137).
This patch adds the option to clang to surface the internal options at driver level.

GCC 7 also turned on -fprofile-update=prefer-atomic when -pthread is specified,
but it has performance regression
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89307). So we don't follow suit.

Differential Revision: https://reviews.llvm.org/D87737

Author: MaskRay

clang/docs/UsersManual.rst

@@ -2172,6 +2172,17 @@ programs using the same instrumentation method as ``-fprofile-generate``.
   profile file, it reads from that file. If ``pathname`` is a directory name,
   it reads from ``pathname/default.profdata``.
 
+.. option:: -fprofile-update[=<method>]
+
+  Unless ``-fsanitize=thread`` is specified, the default is ``single``, which
+  uses non-atomic increments. The counters can be inaccurate under thread
+  contention. ``atomic`` uses atomic increments which is accurate but has
+  overhead. ``prefer-atomic`` will be transformed to ``atomic`` when supported
+  by the target, or ``single`` otherwise.
+
+  This option currently works with ``-fprofile-arcs`` and ``-fprofile-instr-generate``,
+  but not with ``-fprofile-generate``.
+
 Disabling Instrumentation
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/CodeGenOptions.def

@@ -185,6 +185,7 @@ CODEGENOPT(ObjCConvertMessagesToRuntimeCalls , 1, 1)
 VALUE_CODEGENOPT(OptimizationLevel, 2, 0) ///< The -O[0-3] option specified.
 VALUE_CODEGENOPT(OptimizeSize, 2, 0) ///< If -Os (==1) or -Oz (==2) is specified.
 
+CODEGENOPT(AtomicProfileUpdate , 1, 0) ///< Set -fprofile-update=atomic
 /// 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

@@ -853,6 +853,9 @@ def fprofile_filter_files_EQ : Joined<["-"], "fprofile-filter-files=">,
 def fprofile_exclude_files_EQ : Joined<["-"], "fprofile-exclude-files=">,
     Group<f_Group>, Flags<[CC1Option, CoreOption]>,
     HelpText<"Instrument only functions from files where names don't match all the regexes separated by a semi-colon">;
+def fprofile_update_EQ : Joined<["-"], "fprofile-update=">,
+    Group<f_Group>, Flags<[CC1Option, CoreOption]>, Values<"atomic,prefer-atomic,single">,
+    MetaVarName<"<method>">, HelpText<"Set update method of profile counters (atomic,prefer-atomic,single)">;
 def forder_file_instrumentation : Flag<["-"], "forder-file-instrumentation">,
     Group<f_Group>, Flags<[CC1Option, CoreOption]>,
     HelpText<"Generate instrumented code to collect order file into default.profraw file (overridden by '=' form of option or LLVM_PROFILE_FILE env var)">;

clang/lib/CodeGen/BackendUtil.cpp

@@ -570,7 +570,7 @@ static Optional<GCOVOptions> getGCOVOptions(const CodeGenOptions &CodeGenOpts,
   Options.NoRedZone = CodeGenOpts.DisableRedZone;
   Options.Filter = CodeGenOpts.ProfileFilterFiles;
   Options.Exclude = CodeGenOpts.ProfileExcludeFiles;
-  Options.Atomic = LangOpts.Sanitize.has(SanitizerKind::Thread);
+  Options.Atomic = CodeGenOpts.AtomicProfileUpdate;
   return Options;
 }
 
@@ -582,10 +582,7 @@ getInstrProfOptions(const CodeGenOptions &CodeGenOpts,
   InstrProfOptions Options;
   Options.NoRedZone = CodeGenOpts.DisableRedZone;
   Options.InstrProfileOutput = CodeGenOpts.InstrProfileOutput;
-
-  // TODO: Surface the option to emit atomic profile counter increments at
-  // the driver level.
-  Options.Atomic = LangOpts.Sanitize.has(SanitizerKind::Thread);
+  Options.Atomic = CodeGenOpts.AtomicProfileUpdate;
   return Options;
 }
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -868,6 +868,17 @@ static void addPGOAndCoverageFlags(const ToolChain &TC, Compilation &C,
     CmdArgs.push_back(Args.MakeArgString(Twine("-fprofile-filter-files=" + v)));
   }
 
+  if (const auto *A = Args.getLastArg(options::OPT_fprofile_update_EQ)) {
+    StringRef Val = A->getValue();
+    if (Val == "atomic" || Val == "prefer-atomic")
+      CmdArgs.push_back("-fprofile-update=atomic");
+    else if (Val != "single")
+      D.Diag(diag::err_drv_unsupported_option_argument)
+          << A->getOption().getName() << Val;
+  } else if (TC.getSanitizerArgs().needsTsanRt()) {
+    CmdArgs.push_back("-fprofile-update=atomic");
+  }
+
   // Leave -fprofile-dir= an unused argument unless .gcda emission is
   // enabled. To be polite, with '-fprofile-arcs -fno-profile-arcs' consider
   // the flag used. There is no -fno-profile-dir, so the user has no

clang/lib/Frontend/CompilerInvocation.cpp

@@ -884,6 +884,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.DebugRangesBaseAddress = Args.hasArg(OPT_fdebug_ranges_base_address);
 
   setPGOInstrumentor(Opts, Args, Diags);
+  Opts.AtomicProfileUpdate = Args.hasArg(OPT_fprofile_update_EQ);
   Opts.InstrProfileOutput =
       std::string(Args.getLastArgValue(OPT_fprofile_instrument_path_EQ));
   Opts.ProfileInstrumentUsePath =

clang/test/CodeGen/code-coverage-tsan.c

@@ -1,11 +1,12 @@
-/// -fsanitize=thread requires the (potentially concurrent) counter updates to be atomic.
-// RUN: %clang_cc1 %s -triple x86_64 -emit-llvm -fsanitize=thread -femit-coverage-notes -femit-coverage-data \
+/// -fprofile-update=atomic (implied by -fsanitize=thread) requires the
+/// (potentially concurrent) counter updates to be atomic.
+// RUN: %clang_cc1 %s -triple x86_64 -emit-llvm -fprofile-update=atomic -femit-coverage-notes -femit-coverage-data \
 // RUN:   -coverage-notes-file /dev/null -coverage-data-file /dev/null -o - | FileCheck %s
 
 // CHECK-LABEL: void @foo()
 /// Two counters are incremented by __tsan_atomic64_fetch_add.
-// CHECK:         call i64 @__tsan_atomic64_fetch_add
-// CHECK-NEXT:    call i32 @__tsan_atomic32_fetch_sub
+// CHECK:         atomicrmw add i64* {{.*}} @__llvm_gcov_ctr
+// CHECK-NEXT:    atomicrmw sub i32*
 
 _Atomic(int) cnt;
 void foo() { cnt--; }

clang/test/CodeGen/tsan-instrprof-atomic.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -emit-llvm -fprofile-instrument=clang -fsanitize=thread -o - | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -fprofile-instrument=clang -fprofile-update=atomic -o - | FileCheck %s
 
 // CHECK: define {{.*}}@foo
 // CHECK-NOT: load {{.*}}foo

clang/test/Driver/fprofile-update.c

@@ -0,0 +1,15 @@
+/// For -fprofile-instr-generate and -fprofile-arcs, increment counters atomically
+/// if -fprofile-update={atomic,prefer-atomic} or -fsanitize=thread is specified.
+// RUN: %clang -### %s -c -target x86_64-linux -fsanitize=thread %s 2>&1 | FileCheck %s
+// RUN: %clang -### %s -c -fprofile-update=atomic 2>&1 | FileCheck %s
+// RUN: %clang -### %s -c -fprofile-update=prefer-atomic 2>&1 | FileCheck %s
+
+// CHECK: "-fprofile-update=atomic"
+
+// RUN: %clang -### %s -c -fprofile-update=atomic -fprofile-update=single 2>&1 | FileCheck %s --check-prefix=SINGLE
+
+// SINGLE-NOT: "-fprofile-update=atomic"
+
+// RUN: not %clang %s -c -fprofile-update=unknown 2>&1 | FileCheck %s --check-prefix=ERROR
+
+// ERROR: error: unsupported argument 'unknown' to option 'fprofile-update='