Clang change: Do not inline hot callsites for samplepgo in thinlto compile phase.

[danielcdh]

Summary

Because SamplePGO passes will be invoked twice in ThinLTO build: once at compile phase, the other at backend. We want to make sure the IR at the 2nd phase matches the hot part in pro
file, thus we do not want to inline hot callsites in the first phase.

[tejohnson]

LGTM

lib/CodeGen/BackendUtil.cpp

void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
 
   // At O0 and O1 we only run the always inliner which is more efficient. At
   // higher optimization levels we run the normal inliner.
   if (CodeGenOpts.OptimizationLevel <= 1) {
     bool InsertLifetimeIntrinsics = (CodeGenOpts.OptimizationLevel != 0 &&
                                      !CodeGenOpts.DisableLifetimeMarkers);
     PMBuilder.Inliner = createAlwaysInlinerLegacyPass(InsertLifetimeIntrinsics);
   } else {
+    // We do not want to inline hot callsites for SamplePGO module-summary build
+    // because profile annotation will happen again in ThinLTO backend, and we
+    // want the IR of the hot path to match the profile.
     PMBuilder.Inliner = createFunctionInliningPass(
-        CodeGenOpts.OptimizationLevel, CodeGenOpts.OptimizeSize);
+        CodeGenOpts.OptimizationLevel, CodeGenOpts.OptimizeSize,
+        (!CodeGenOpts.SampleProfileFile.empty() &&
+         CodeGenOpts.EmitSummaryIndex));
   }
 
   PMBuilder.OptLevel = CodeGenOpts.OptimizationLevel;
   PMBuilder.SizeLevel = CodeGenOpts.OptimizeSize;
   PMBuilder.BBVectorize = CodeGenOpts.VectorizeBB;
   PMBuilder.SLPVectorize = CodeGenOpts.VectorizeSLP;
   PMBuilder.LoopVectorize = CodeGenOpts.VectorizeLoop;
 

test/CodeGen/Inputs/pgo-sample-thinlto-summary.prof

+bar:100:100
+ 2: 2000 foo:2000

test/CodeGen/pgo-sample-thinlto-summary.c

+// RUN: %clang_cc1 -O2 -fprofile-sample-use=%S/Inputs/pgo-sample-thinlto-summary.prof %s -emit-llvm -o - 2>&1 | FileCheck %s -check-prefix=INLINE
+// RUN: %clang_cc1 -O2 -fprofile-sample-use=%S/Inputs/pgo-sample-thinlto-summary.prof %s -emit-llvm -flto=thin -o - 2>&1 | FileCheck %s -check-prefix=NOINLINE
+// Checks if hot call is inlined by normal compile, but not inlined by
+// thinlto compile.
+
+int baz(int);
+int g;
+
+void foo(int n) {
+  for (int i = 0; i < n; i++)
+    g += baz(i);
+}
+
+// INLINE-NOT: call{{.*}}foo
+// NOINLINE: call{{.*}}foo
+void bar(int n) {
+  for (int i = 0; i < n; i++)
+    foo(i);
+}