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

[Ellis Hoag via cfe-commits]

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@@ -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>());
+    }
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ellishg wrote:

After looking at this a bit closer, I'm not sure why it needs to be tied to closely to SamplePGO. Couldn't we move this out of the `LoadSampleProfile` and move it after `IsPGOInstrUse/IsCtxProfUse`? That way we can use IRPGO, CSIRPGO, and SamplePGO profile counts to block instrumentation hot functions.

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