[llvm] [PGO] Preserve analysis results when nothing was instrumented (PR #93421)

[Ellis Hoag via llvm-commits]

================
@@ -143,12 +147,47 @@ struct PGOInstrumentationGenTest
   }
 };
 
+struct PGOInstrumentationGenInstrumentTest
+    : PGOInstrumentationGenTest,
+      WithParamInterface<std::tuple<StringRef, StringRef>> {};
+
 static constexpr StringRef CodeWithFuncDefs = R"(
   define i32 @f(i32 %n) {
   entry:
     ret i32 0
   })";
 
+INSTANTIATE_TEST_SUITE_P(
+    PGOInstrumetationGenTestSuite, PGOInstrumentationGenInstrumentTest,
+    Values(std::make_tuple(CodeWithFuncDefs, "instrument_function_defs")),
+    PGOTestName<PGOInstrumentationGenInstrumentTest::ParamType>());
+
+TEST_P(PGOInstrumentationGenInstrumentTest, Instrumented) {
+  const StringRef Code = std::get<0>(GetParam());
+  parseAssembly(Code);
+
+  ASSERT_THAT(M, NotNull());
+
+  Sequence PassSequence;
+  EXPECT_CALL(MMAHandle, run(Ref(*M), _))
+      .InSequence(PassSequence)
+      .WillOnce(DoDefault());
+  EXPECT_CALL(MMAHandle, invalidate(Ref(*M), _, _))
+      .InSequence(PassSequence)
+      .WillOnce(DoDefault());
+
+  MPM.run(*M, MAM);
+
+  const auto *IRInstrVar =
+      M->getNamedGlobal(INSTR_PROF_QUOTE(INSTR_PROF_RAW_VERSION_VAR));
+  EXPECT_THAT(IRInstrVar, NotNull());
----------------
ellishg wrote:

```suggestion
  ASSERT_THAT(IRInstrVar, NotNull());
```
I believe this will stop the test if null, rather than trying to continue.

https://github.com/llvm/llvm-project/pull/93421