Revert "Revert "[misexpect] Re-implement MisExpect Diagnostics""

I mistakenly reverted my commit, so I'm relanding it.

This reverts commit 10866a1.

Author: ilovepi

clang/docs/MisExpect.rst

@@ -0,0 +1,75 @@
+===================
+Misexpect
+===================
+.. contents::
+
+.. toctree::
+   :maxdepth: 1
+
+When developers use ``llvm.expect`` intrinsics, i.e., through use of
+``__builtin_expect(...)``, they are trying to communicate how their code is
+expected to behave at runtime to the optimizer. These annotations, however, can
+be incorrect for a variety of reasons: changes to the code base invalidate them
+silently, the developer mis-annotated them (e.g., using ``LIKELY`` instead of
+``UNLIKELY``), or perhaps they assumed something incorrectly when they wrote
+the annotation. Regardless of why, it is useful to detect these situations so
+that the optimizer can make more useful decisions about the code. 
+
+MisExpect diagnostics are intended to help developers identify and address
+these situations, by comparing the branch weights added by the ``llvm.expect``
+intrinsic to those collected through profiling. Whenever these values are
+mismatched, a diagnostic is surfaced to the user. Details on how the checks
+operate in the LLVM backed can be found in LLVM's documentation.
+
+By default MisExpect checking is quite strict, because the use of the
+``llvm.expect`` intrinsic is designed for specialized cases, where the outcome
+of a condition is severely skewed. As a result, the optimizer can be extremely
+aggressive, which can result in performance degradation if the outcome is less
+predictable than the annotation suggests. Even when the annotation is correct
+90% of the time, it may be beneficial to either remove the annotation or to use
+a different intrinsic that can communicate the probability more directly.
+
+Because this may be too strict, MisExpect diagnostics are not enabled by
+default, and support an additional flag to tolerate some deviation from the
+exact thresholds. The ``-fdiagnostic-misexpect-tolerance=N`` accepts
+deviations when comparing branch weights within ``N%`` of the expected values.
+So passing ``-fdiagnostic-misexpect-tolerance=5`` will not report diagnostic messages
+if the branch weight from the profile is within 5% of the weight added by
+the ``llvm.expect`` intrinsic.
+
+MisExpect diagnostics are also available in the form of optimization remarks,
+which can be serialized and processed through the ``opt-viewer.py``
+scripts in LLVM.
+
+.. option:: -Rpass=misexpect
+
+  Enables optimization remarks for misexpect when profiling data conflicts with
+  use of ``llvm.expect`` intrinsics.
+
+
+.. option:: -Wmisexpect
+
+  Enables misexpect warnings when profiling data conflicts with use of
+  ``llvm.expect`` intrinsics.
+
+.. option:: -fdiagnostic-misexpect-tolerance=N
+
+   Relaxes misexpect checking to tolerate profiling values within N% of the 
+   expected branch weight. e.g., a value of ``N=5`` allows misexpect to check against
+   ``0.95 * Threshold``
+
+LLVM supports 4 types of profile formats: Frontend, IR, CS-IR, and
+Sampling. MisExpect Diagnostics are compatible with all Profiling formats.
+
++----------------+--------------------------------------------------------------------------------------+
+| Profile Type   | Description                                                                          |
++================+======================================================================================+
+| Frontend       | Profiling instrumentation added during compilation by the frontend, i.e. ``clang``    |
++----------------+--------------------------------------------------------------------------------------+
+| IR             | Profiling instrumentation added during by the LLVM backend                           |
++----------------+--------------------------------------------------------------------------------------+
+| CS-IR          | Context Sensitive IR based profiles                                                  |
++----------------+--------------------------------------------------------------------------------------+
+| Sampling       | Profiles collected through sampling with external tools, such as ``perf`` on Linux   |
++----------------+--------------------------------------------------------------------------------------+
+

clang/docs/ReleaseNotes.rst

@@ -68,6 +68,9 @@ Improvements to Clang's diagnostics
   constants that are not representable in a casted value. For example,
   ``(float) f == 0.1`` is always false.
 
+- ``-Wmisexpect`` warns when the branch weights collected during profiling
+  conflict with those added by ``llvm.expect``.
+
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 

clang/include/clang/Basic/CodeGenOptions.def

@@ -175,6 +175,7 @@ CODEGENOPT(NoExecStack       , 1, 0) ///< Set when -Wa,--noexecstack is enabled.
 CODEGENOPT(FatalWarnings     , 1, 0) ///< Set when -Wa,--fatal-warnings is
                                      ///< enabled.
 CODEGENOPT(NoWarn            , 1, 0) ///< Set when -Wa,--no-warn is enabled.
+CODEGENOPT(MisExpect         , 1, 0) ///< Set when -Wmisexpect is enabled
 CODEGENOPT(EnableSegmentedStacks , 1, 0) ///< Set when -fsplit-stack is enabled.
 CODEGENOPT(NoInlineLineTables, 1, 0) ///< Whether debug info should contain
                                      ///< inline line tables.

clang/include/clang/Basic/CodeGenOptions.h

@@ -420,6 +420,10 @@ class CodeGenOptions : public CodeGenOptionsBase {
   /// If threshold option is not specified, it is disabled by default.
   Optional<uint64_t> DiagnosticsHotnessThreshold = 0;
 
+  /// The maximum percentage profiling weights can deviate from the expected
+  /// values in order to be included in misexpect diagnostics.
+  Optional<uint64_t> DiagnosticsMisExpectTolerance = 0;
+
 public:
   // Define accessors/mutators for code generation options of enumeration type.
 #define CODEGENOPT(Name, Bits, Default)

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -149,6 +149,8 @@ def err_drv_invalid_darwin_version : Error<
   "invalid Darwin version number: %0">;
 def err_drv_invalid_diagnotics_hotness_threshold : Error<
   "invalid argument in '%0', only integer or 'auto' is supported">;
+def err_drv_invalid_diagnotics_misexpect_tolerance : Error<
+  "invalid argument in '%0', only integers are supported">;
 def err_drv_missing_argument : Error<
   "argument to '%0' is missing (expected %1 value%s1)">;
 def err_drv_invalid_Xarch_argument_with_args : Error<
@@ -374,6 +376,9 @@ def warn_drv_empty_joined_argument : Warning<
 def warn_drv_diagnostics_hotness_requires_pgo : Warning<
   "argument '%0' requires profile-guided optimization information">,
   InGroup<UnusedCommandLineArgument>;
+def warn_drv_diagnostics_misexpect_requires_pgo : Warning<
+  "argument '%0' requires profile-guided optimization information">,
+  InGroup<UnusedCommandLineArgument>;
 def warn_drv_clang_unsupported : Warning<
   "the clang compiler does not support '%0'">;
 def warn_drv_deprecated_arg : Warning<

clang/include/clang/Basic/DiagnosticFrontendKinds.td

@@ -311,6 +311,11 @@ def warn_profile_data_missing : Warning<
 def warn_profile_data_unprofiled : Warning<
   "no profile data available for file \"%0\"">,
   InGroup<ProfileInstrUnprofiled>;
+def warn_profile_data_misexpect : Warning<
+  "Potential performance regression from use of __builtin_expect(): "
+  "Annotation was correct on %0 of profiled executions.">,
+  BackendInfo,
+  InGroup<MisExpect>;
 } // end of instrumentation issue category
 
 }

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1249,6 +1249,7 @@ def BackendWarningAttributes : DiagGroup<"attribute-warning">;
 def ProfileInstrMissing : DiagGroup<"profile-instr-missing">;
 def ProfileInstrOutOfDate : DiagGroup<"profile-instr-out-of-date">;
 def ProfileInstrUnprofiled : DiagGroup<"profile-instr-unprofiled">;
+def MisExpect : DiagGroup<"misexpect">;
 
 // AddressSanitizer frontend instrumentation remarks.
 def SanitizeAddressRemarks : DiagGroup<"sanitize-address">;

clang/include/clang/Driver/Options.td

@@ -1424,6 +1424,9 @@ def fdiagnostics_hotness_threshold_EQ : Joined<["-"], "fdiagnostics-hotness-thre
     Group<f_Group>, Flags<[CC1Option]>, MetaVarName<"<value>">,
     HelpText<"Prevent optimization remarks from being output if they do not have at least this profile count. "
     "Use 'auto' to apply the threshold from profile summary">;
+def fdiagnostics_misexpect_tolerance_EQ : Joined<["-"], "fdiagnostics-misexpect-tolerance=">,
+    Group<f_Group>, Flags<[CC1Option]>, MetaVarName<"<value>">,
+    HelpText<"Prevent misexpect diagnostics from being output if the profile counts are within N% of the expected. ">;
 defm diagnostics_show_option : BoolFOption<"diagnostics-show-option",
     DiagnosticOpts<"ShowOptionNames">, DefaultTrue,
     NegFlag<SetFalse, [CC1Option]>, PosFlag<SetTrue, [], "Print option name with mappable diagnostics">>;

clang/lib/CodeGen/BackendUtil.cpp

@@ -650,6 +650,7 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
           Entry.IgnoreSysRoot ? Entry.Path : HSOpts.Sysroot + Entry.Path);
   Options.MCOptions.Argv0 = CodeGenOpts.Argv0;
   Options.MCOptions.CommandLineArgs = CodeGenOpts.CommandLineArgs;
+  Options.MisExpect = CodeGenOpts.MisExpect;
 
   return true;
 }

clang/lib/CodeGen/CodeGenAction.cpp

@@ -340,6 +340,15 @@ namespace clang {
           CodeGenOpts.getProfileUse() != CodeGenOptions::ProfileNone)
         Ctx.setDiagnosticsHotnessRequested(true);
 
+      if (CodeGenOpts.MisExpect) {
+        Ctx.setMisExpectWarningRequested(true);
+      }
+
+      if (CodeGenOpts.DiagnosticsMisExpectTolerance) {
+        Ctx.setDiagnosticsMisExpectTolerance(
+            CodeGenOpts.DiagnosticsMisExpectTolerance);
+      }
+
       // Link each LinkModule into our module.
       if (LinkInModules())
         return;
@@ -440,6 +449,9 @@ namespace clang {
     void OptimizationFailureHandler(
         const llvm::DiagnosticInfoOptimizationFailure &D);
     void DontCallDiagHandler(const DiagnosticInfoDontCall &D);
+    /// Specialized handler for misexpect warnings.
+    /// Note that misexpect remarks are emitted through ORE
+    void MisExpectDiagHandler(const llvm::DiagnosticInfoMisExpect &D);
   };
 
   void BackendConsumer::anchor() {}
@@ -821,6 +833,25 @@ void BackendConsumer::DontCallDiagHandler(const DiagnosticInfoDontCall &D) {
       << llvm::demangle(D.getFunctionName().str()) << D.getNote();
 }
 
+void BackendConsumer::MisExpectDiagHandler(
+    const llvm::DiagnosticInfoMisExpect &D) {
+  StringRef Filename;
+  unsigned Line, Column;
+  bool BadDebugInfo = false;
+  FullSourceLoc Loc =
+      getBestLocationFromDebugLoc(D, BadDebugInfo, Filename, Line, Column);
+
+  Diags.Report(Loc, diag::warn_profile_data_misexpect) << D.getMsg().str();
+
+  if (BadDebugInfo)
+    // If we were not able to translate the file:line:col information
+    // back to a SourceLocation, at least emit a note stating that
+    // we could not translate this location. This can happen in the
+    // case of #line directives.
+    Diags.Report(Loc, diag::note_fe_backend_invalid_loc)
+        << Filename << Line << Column;
+}
+
 /// This function is invoked when the backend needs
 /// to report something to the user.
 void BackendConsumer::DiagnosticHandlerImpl(const DiagnosticInfo &DI) {
@@ -895,6 +926,9 @@ void BackendConsumer::DiagnosticHandlerImpl(const DiagnosticInfo &DI) {
   case llvm::DK_DontCall:
     DontCallDiagHandler(cast<DiagnosticInfoDontCall>(DI));
     return;
+  case llvm::DK_MisExpect:
+    MisExpectDiagHandler(cast<DiagnosticInfoMisExpect>(DI));
+    return;
   default:
     // Plugin IDs are not bound to any value as they are set dynamically.
     ComputeDiagRemarkID(Severity, backend_plugin, DiagID);

clang/lib/Frontend/CompilerInvocation.cpp

@@ -106,6 +106,20 @@ using namespace driver;
 using namespace options;
 using namespace llvm::opt;
 
+//===----------------------------------------------------------------------===//
+// Helpers.
+//===----------------------------------------------------------------------===//
+
+// Parse misexpect tolerance argument value.
+// Valid option values are integers in the range [0, 100)
+inline Expected<Optional<uint64_t>> parseToleranceOption(StringRef Arg) {
+  int64_t Val;
+  if (Arg.getAsInteger(10, Val))
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "Not an integer: %s", Arg.data());
+  return Val;
+}
+
 //===----------------------------------------------------------------------===//
 // Initialization.
 //===----------------------------------------------------------------------===//
@@ -1952,6 +1966,21 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
     }
   }
 
+  if (auto *arg =
+          Args.getLastArg(options::OPT_fdiagnostics_misexpect_tolerance_EQ)) {
+    auto ResultOrErr = parseToleranceOption(arg->getValue());
+
+    if (!ResultOrErr) {
+      Diags.Report(diag::err_drv_invalid_diagnotics_misexpect_tolerance)
+          << "-fdiagnostics-misexpect-tolerance=";
+    } else {
+      Opts.DiagnosticsMisExpectTolerance = *ResultOrErr;
+      if (!UsingProfile)
+        Diags.Report(diag::warn_drv_diagnostics_misexpect_requires_pgo)
+            << "-fdiagnostics-misexpect-tolerance=";
+    }
+  }
+
   // If the user requested to use a sample profile for PGO, then the
   // backend will need to track source location information so the profile
   // can be incorporated into the IR.
@@ -4497,6 +4526,13 @@ bool CompilerInvocation::CreateFromArgsImpl(
   if (Res.getFrontendOpts().ProgramAction == frontend::RewriteObjC)
     LangOpts.ObjCExceptions = 1;
 
+  for (auto Warning : Res.getDiagnosticOpts().Warnings) {
+    if (Warning == "misexpect" &&
+        !Diags.isIgnored(diag::warn_profile_data_misexpect, SourceLocation())) {
+      Res.getCodeGenOpts().MisExpect = true;
+    }
+  }
+
   if (LangOpts.CUDA) {
     // During CUDA device-side compilation, the aux triple is the
     // triple used for host compilation.

clang/test/Profile/Inputs/misexpect-branch-nonconst-expect-arg.proftext

@@ -0,0 +1,8 @@
+bar
+# Func Hash:
+11262309464
+# Num Counters:
+2
+# Counter Values:
+200000
+2

clang/test/Profile/Inputs/misexpect-branch.proftext

@@ -0,0 +1,17 @@
+bar
+# Func Hash:
+45795613684824
+# Num Counters:
+2
+# Counter Values:
+200000
+180000
+
+fizz
+# Func Hash:
+45795613684824
+# Num Counters:
+2
+# Counter Values:
+200000
+18000

clang/test/Profile/Inputs/misexpect-switch-default-only.proftext

@@ -0,0 +1,12 @@
+main
+# Func Hash:
+79676873694057560
+# Num Counters:
+5
+# Counter Values:
+1
+20
+20000
+20000
+20000
+

clang/test/Profile/Inputs/misexpect-switch-default.proftext

@@ -0,0 +1,16 @@
+main
+# Func Hash:
+8734802134600123338
+# Num Counters:
+9
+# Counter Values:
+1
+20000
+20000
+4066
+11889
+0
+0
+4045
+0
+

clang/test/Profile/Inputs/misexpect-switch-nonconst.proftext

@@ -0,0 +1,16 @@
+main
+# Func Hash:
+3721743393642630379
+# Num Counters:
+10
+# Counter Values:
+1
+20
+20000
+20000
+1
+0
+0
+0
+19999
+0

clang/test/Profile/Inputs/misexpect-switch.proftext

@@ -0,0 +1,32 @@
+main
+# Func Hash:
+872687477373597607
+# Num Counters:
+9
+# Counter Values:
+1
+20
+20000
+20000
+3
+3
+1
+3
+19990
+
+random_sample
+# Func Hash:
+24
+# Num Counters:
+1
+# Counter Values:
+19990
+
+sum
+# Func Hash:
+24
+# Num Counters:
+1
+# Counter Values:
+3
+