[clang] [llvm] [InstrPGO] Instrument sampling profile based cold function (PR #109837)

[Lei Wang via cfe-commits]

================
@@ -1119,6 +1125,18 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
       // removed.
       MPM.addPass(
           PGOIndirectCallPromotion(true /* IsInLTO */, true /* SamplePGO */));
+
+    if (InstrumentSampleColdFuncPath.getNumOccurrences() &&
+        Phase != ThinOrFullLTOPhase::ThinLTOPostLink) {
+      assert(!InstrumentSampleColdFuncPath.empty() &&
+             "File path is requeired for instrumentation generation");
+      InstrumentColdFunctionCoverage = true;
+      addPreInlinerPasses(MPM, Level, Phase);
+      addPGOInstrPasses(MPM, Level, /* RunProfileGen */ true,
+                        /* IsCS */ false, /* AtomicCounterUpdate */ false,
+                        InstrumentSampleColdFuncPath, "",
+                        IntrusiveRefCntPtr<vfs::FileSystem>());
+    }
----------------
wlei-llvm wrote:

do you mean the `sample` in `InstrumentSampleColdFuncPath`flag or all other variables(like `IsSampleColdFuncCovGen`)?  I thought something like:

```
if (IsSampleColdFuncCovGen || IsXXXColdFuncCovGen) {
     addPGOInstrPasses(.., .., InstrumentColdFuncCoveragePath, .. )
}
```
`InstrumentColdFuncCoveragePath` would be a general flag that can be used for all cold function coverage case. but currently `IsSampleColdFuncCovGen` only represents for sampling PGO cold func. And If we want to extend it in future, then we can add more bool flag IsXXXColdFuncCovGen... 

I also added an assertion:
```
  assert((InstrumentColdFuncCoveragePath.empty() || LoadSampleProfile) &&
         "Sampling-based cold functon coverage is not supported without "
         "providing sampling PGO profile");
```
Seems I have to remove that if we want it to be general. (just curious) do you plan to extend it for your case? 

https://github.com/llvm/llvm-project/pull/109837