NewPM: Improve/fix GCOV - which needs to run early in the pass pipeline.

Using a new extension point in the new PM, register GCOV at the start of
the pipeline rather than the end.

llvm-svn: 323167
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index c755723..6d42aac 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -909,6 +909,9 @@
     bool IsLTO = CodeGenOpts.PrepareForLTO;
 
     if (CodeGenOpts.OptimizationLevel == 0) {
+      if (Optional<GCOVOptions> Options = getGCOVOptions(CodeGenOpts))
+        MPM.addPass(GCOVProfilerPass(*Options));
+
       // Build a minimal pipeline based on the semantics required by Clang,
       // which is just that always inlining occurs.
       MPM.addPass(AlwaysInlinerPass());
@@ -932,6 +935,10 @@
             [](FunctionPassManager &FPM, PassBuilder::OptimizationLevel Level) {
               FPM.addPass(BoundsCheckingPass());
             });
+      if (Optional<GCOVOptions> Options = getGCOVOptions(CodeGenOpts))
+        PB.registerPipelineStartEPCallback([Options](ModulePassManager &MPM) {
+          MPM.addPass(GCOVProfilerPass(*Options));
+        });
 
       if (IsThinLTO) {
         MPM = PB.buildThinLTOPreLinkDefaultPipeline(
@@ -945,9 +952,6 @@
                                                CodeGenOpts.DebugPassManager);
       }
     }
-    if (Optional<GCOVOptions> Options = getGCOVOptions(CodeGenOpts)) {
-      MPM.addPass(GCOVProfilerPass(*Options));
-    }
   }
 
   // FIXME: We still use the legacy pass manager to do code generation. We