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

[Lei Wang 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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wlei-llvm 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.

Ah, good point, moved them closer to other IRPGO passes. Thanks for the suggestion!

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