[Coverage] Suppress covmap and profdata for system headers. (#97952)

With `system-headers-coverage=false`, functions defined in system
headers were not instrumented but corresponding covmaps were emitted. It
caused wasting covmap and profraw.

This change improves:

- Reduce object size (due to reduced covmap)
- Reduce size of profraw (uninstrumented system headers occupied
counters)
- Smarter view of coverage report. Stubs of uninstrumented system
headers will be no longer seen.

clang/lib/CodeGen/CodeGenModule.cpp

@@ -7165,6 +7165,9 @@ void CodeGenModule::AddDeferredUnusedCoverageMapping(Decl *D) {
     SourceManager &SM = getContext().getSourceManager();
     if (LimitedCoverage && SM.getMainFileID() != SM.getFileID(D->getBeginLoc()))
       break;
+    if (!llvm::coverage::SystemHeadersCoverage &&
+        SM.isInSystemHeader(D->getBeginLoc()))
+      break;
     DeferredEmptyCoverageMappingDecls.try_emplace(D, true);
     break;
   }

clang/lib/CodeGen/CodeGenPGO.cpp

@@ -1044,13 +1044,17 @@ void CodeGenPGO::assignRegionCounters(GlobalDecl GD, llvm::Function *Fn) {
   if (Fn->hasFnAttribute(llvm::Attribute::SkipProfile))
     return;
 
+  SourceManager &SM = CGM.getContext().getSourceManager();
+  if (!llvm::coverage::SystemHeadersCoverage &&
+      SM.isInSystemHeader(D->getLocation()))
+    return;
+
   setFuncName(Fn);
 
   mapRegionCounters(D);
   if (CGM.getCodeGenOpts().CoverageMapping)
     emitCounterRegionMapping(D);
   if (PGOReader) {
-    SourceManager &SM = CGM.getContext().getSourceManager();
     loadRegionCounts(PGOReader, SM.isInMainFile(D->getLocation()));
     computeRegionCounts(D);
     applyFunctionAttributes(PGOReader, Fn);

clang/test/CoverageMapping/system_macro.cpp

@@ -5,9 +5,8 @@
 
 // LL_CHECK: @__covrec_
 // LL_W_SYS: [[PROFC:@.*__profc_.*SysTmpl.*]] =
-// LL_WOSYS: [[PROFC:@.*__profc_.*SysTmpl.*]] =
 // LL_W_SYS: @{{.*}}__profd_{{.*}}SysTmpl{{.*}} =
-// LL_WOSYS: @{{.*}}__profd_{{.*}}SysTmpl{{.*}} =
+// LL_WOSYS-NOT: SysTmpl
 
 // LL_CHECK: @llvm.used =
 
@@ -21,7 +20,7 @@
 template <bool f> bool SysTmpl() { return f; }
 // Check SysTmpl() is instrumented or not.
 // LL_W_SYS: load i64, ptr [[PROFC]],
-// LL_WOSYS: load i64, ptr [[PROFC]],
+// LL_WOSYS-NOT: load i64, ptr @__profc_
 
 #else