PGOInstrumentation: Move profile matching warnings to remarks

[dblaikie]

Summary

These messages are expected if the source code has diverged sufficiently
from the code the profile was gathered from. In small enough amounts
they're benign/not actionable, so a warning seems inappropriate/noisy (&
probablematic in -Werror builds) for these kinds of messages.

I also updated some tests around other profile instrumentation related
diagnostics to ensure they are errors (things like failing to load the
profile, finding it's the wrong kind of profile - these are actionable
by the user) & removed one that wasn't reachable/testable, but was
testing an API invariant - replaced that with an assertion.

[davidxl]

Blindly downgrade the warning into remarks can be bad -- profile mismatch problems can go undetected. People may spend more time diagnosing performance regressions due to missed warnings. Worse, we may regress in compiler without noticing.

[dblaikie]

I /think/ this is probably still the right direction, but haven't got the context/prioritization/etc to make progress here, so abandoning (finding retired old branches as I migrate to the git repo from git-svn).

lib/Transforms/Instrumentation/PGOInstrumentation.cpp

handleAllErrors(std::move(E), [&](const InstrProfError &IPE) {
               F.getLinkage() == GlobalValue::AvailableExternallyLinkage));
       }
 
       if (SkipWarning)
         return;
 
       std::string Msg = IPE.message() + std::string(" ") + F.getName().str();
       Ctx.diagnose(
-          DiagnosticInfoPGOProfile(M->getName().data(), Msg, DS_Warning));
+          DiagnosticInfoPGOProfile(M->getName().data(), Msg, DS_Remark));
     });
     return false;
   }
   ProfileRecord = std::move(Result.get());
   std::vector<uint64_t> &CountFromProfile = ProfileRecord.Counts;
 
   NumOfPGOFunc++;
   DEBUG(dbgs() << CountFromProfile.size() << " counts\n");
handleAllErrors(std::move(E), [&](const ErrorInfoBase &EI) {
       Ctx.diagnose(
           DiagnosticInfoPGOProfile(ProfileFileName.data(), EI.message()));
     });
     return false;
   }
 
   std::unique_ptr<IndexedInstrProfReader> PGOReader =
       std::move(ReaderOrErr.get());
-  if (!PGOReader) {
-    Ctx.diagnose(DiagnosticInfoPGOProfile(ProfileFileName.data(),
-                                          StringRef("Cannot get PGOReader")));
-    return false;
-  }
+  assert(PGOReader);
   // TODO: might need to change the warning once the clang option is finalized.
   if (!PGOReader->isIRLevelProfile()) {
     Ctx.diagnose(DiagnosticInfoPGOProfile(
         ProfileFileName.data(), "Not an IR level instrumentation profile"));
     return false;
   }
 
   std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;

test/Transforms/PGOProfile/diag_FE_profile.ll

 ; RUN: llvm-profdata merge %S/Inputs/diag_FE.proftext -o %t.profdata
 ; RUN: not opt < %s -pgo-instr-use -pgo-test-profile-file=%t.profdata -S  2>&1 | FileCheck %s
 ; RUN: not opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -S  2>&1 | FileCheck %s
 
-; CHECK: Not an IR level instrumentation profile
+; CHECK: error: {{.*}}.profdata: Not an IR level instrumentation profile
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 define i32 @foo() {
 entry:
   ret i32 0
 }

test/Transforms/PGOProfile/diag_mismatch.ll

 ; RUN: llvm-profdata merge %S/Inputs/diag.proftext -o %t.profdata
 ; RUN: opt < %s -pgo-instr-use -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s
 ; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s
 
-; CHECK: Function control flow change detected (hash mismatch) foo
+; CHECK: remark: <stdin>: Function control flow change detected (hash mismatch) foo
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 define i32 @foo() {
 entry:
   ret i32 0
 }

test/Transforms/PGOProfile/diag_no_funcprofdata.ll

 ; RUN: llvm-profdata merge %S/Inputs/diag.proftext -o %t.profdata
 ; RUN: opt < %s -pgo-instr-use -pgo-warn-missing-function=true -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s
 ; RUN: opt < %s -passes=pgo-instr-use -pgo-warn-missing-function=true -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s
 
 ; RUN: opt < %s -pgo-instr-use -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s --check-prefix=DEFAULT
 ; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s --check-prefix=DEFAULT
 
-; CHECK: No profile data available for function bar
+; CHECK: remark: <stdin>: No profile data available for function bar
 ; DEFAULT-NOT: No profile data available for function bar
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 define i32 @bar() {
 entry:
   ret i32 0 
 }