[Profile] Add off-by-default -Wprofile-instr-missing warning

[vsk]

Summary

Clang warns that a profile is out-of-date if it can't find a profile
record for any function in a TU. This warning is now noisy because llvm
can dead-strip functions with profiling instrumentation.

To fix this, this patch changes the existing profile out-of-date warning
(-Wprofile-instr-out-of-date) so that it only complains about mismatched
data. Further, it introduces a new, off-by-default warning about missing
function data (-Wprofile-instr-missing).

[xur]

This change gonna hide the missing profile for a function permanently if there is no mismatch. Like, if a user adds a new function without changing existing functions, he will never get a warning if using the old profiles.

In LLVM IR level PGO, we also find the missing profile warning sometime too verbose. We turn missing profile off by default, but not depending on mismatch. I think that is a better method.

[vsk]

Ah ok, so it sounds like a better approach would be to split the missing record message into a separate off-by-default warning. I don't have the time to update this diff this week, but will shoot for the next.

[mehdi_amini]

In D28867#649760, @vsk wrote:

Ah ok, so it sounds like a better approach would be to split the missing record message into a separate off-by-default warning.

I'm in favor of this.

[vsk]

Apologies for the long delay. I've updated this patch so that -Wprofile-instr-out-of-date and -Wprofile-instr-missing are split up, as suggested by Rong and Mehdi.

[xur]

Looks good to me.

cfe/trunk/include/clang/Basic/DiagnosticGroups.td

 def BackendPlugin : DiagGroup<"backend-plugin">;
 def RemarkBackendPlugin : DiagGroup<"remark-backend-plugin">;
 def BackendOptimizationRemark : DiagGroup<"pass">;
 def BackendOptimizationRemarkMissed : DiagGroup<"pass-missed">;
 def BackendOptimizationRemarkAnalysis : DiagGroup<"pass-analysis">;
 def BackendOptimizationFailure : DiagGroup<"pass-failed">;
 
 // Instrumentation based profiling warnings.
+def ProfileInstrMissing : DiagGroup<"profile-instr-missing">;
 def ProfileInstrOutOfDate : DiagGroup<"profile-instr-out-of-date">;
 def ProfileInstrUnprofiled : DiagGroup<"profile-instr-unprofiled">;
 
 // AddressSanitizer frontend instrumentation remarks.
 def SanitizeAddressRemarks : DiagGroup<"sanitize-address">;
 
 // Issues with serialized diagnostics.
 def SerializedDiagnostics : DiagGroup<"serialized-diagnostics">;

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 let CategoryName = "Documentation Issue" in {
 def warn_not_a_doxygen_trailing_member_comment : Warning<
   "not a Doxygen trailing comment">, InGroup<Documentation>, DefaultIgnore;
 } // end of documentation issue category
 
 let CategoryName = "Instrumentation Issue" in {
 def warn_profile_data_out_of_date : Warning<
   "profile data may be out of date: of %0 function%s0, %1 %plural{1:has|:have}1"
-  " no data and %2 %plural{1:has|:have}2 mismatched data that will be ignored">,
+  " mismatched data that will be ignored">,
   InGroup<ProfileInstrOutOfDate>;
+def warn_profile_data_missing : Warning<
+  "profile data may be incomplete: of %0 function%s0, %1 %plural{1:has|:have}1"
+  " no data">,
+  InGroup<ProfileInstrMissing>,
+  DefaultIgnore;
 def warn_profile_data_unprofiled : Warning<
   "no profile data available for file \"%0\"">,
   InGroup<ProfileInstrUnprofiled>;
 
 } // end of instrumentation issue category
 
 let CategoryName = "Nullability Issue" in {
 

cfe/trunk/lib/CodeGen/CodeGenModule.cpp

 void InstrProfStats::reportDiagnostics(DiagnosticsEngine &Diags,
                                        StringRef MainFile) {
   if (!hasDiagnostics())
     return;
   if (VisitedInMainFile > 0 && VisitedInMainFile == MissingInMainFile) {
     if (MainFile.empty())
       MainFile = "<stdin>";
     Diags.Report(diag::warn_profile_data_unprofiled) << MainFile;
-  } else
-    Diags.Report(diag::warn_profile_data_out_of_date) << Visited << Missing
-                                                      << Mismatched;
+  } else {
+    if (Mismatched > 0)
+      Diags.Report(diag::warn_profile_data_out_of_date) << Visited << Mismatched;
+
+    if (Missing > 0)
+      Diags.Report(diag::warn_profile_data_missing) << Visited << Missing;
+  }
 }
 
 void CodeGenModule::Release() {
   EmitDeferred();
   applyGlobalValReplacements();
   applyReplacements();
   checkAliases();
   EmitCXXGlobalInitFunc();

cfe/trunk/test/Profile/c-outdated-data.c

 // Test that outdated data is ignored.
 
 // FIXME: It would be nice to use -verify here instead of FileCheck, but -verify
 // doesn't play well with warnings that have no line number.
 
 // RUN: llvm-profdata merge %S/Inputs/c-outdated-data.proftext -o %t.profdata
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9 -main-file-name c-outdated-data.c %s -o /dev/null -emit-llvm -fprofile-instrument-use-path=%t.profdata -Wprofile-instr-dropped 2>&1 | FileCheck %s
-// CHECK: warning: profile data may be out of date: of 3 functions, 1 has no data and 1 has mismatched data that will be ignored
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9 -main-file-name c-outdated-data.c %s -o /dev/null -emit-llvm -fprofile-instrument-use-path=%t.profdata 2>&1 | FileCheck %s -check-prefix=NO_MISSING
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9 -main-file-name c-outdated-data.c %s -o /dev/null -emit-llvm -Wprofile-instr-missing -fprofile-instrument-use-path=%t.profdata 2>&1 | FileCheck %s -check-prefix=WITH_MISSING
+
+// NO_MISSING: warning: profile data may be out of date: of 3 functions, 1 has mismatched data that will be ignored
+// NO_MISSING-NOT: 1 has no data
+
+// WITH_MISSING: warning: profile data may be out of date: of 3 functions, 1 has mismatched data that will be ignored
+// WITH_MISSING: warning: profile data may be incomplete: of 3 functions, 1 has no data
 
 void no_usable_data() {
   int i = 0;
 
   if (i) {}
-
-#ifdef GENERATE_OUTDATED_DATA
-  if (i) {}
-#endif
 }
 
-#ifndef GENERATE_OUTDATED_DATA
 void no_data() {
 }
-#endif
 
 int main(int argc, const char *argv[]) {
   no_usable_data();
   return 0;
 }