[Coverage] Map regions from system headers

[gulfem]

Summary

Originally, the following commit removed mapping coverage regions for system headers:
https://github.com/llvm/llvm-project/commit/93205af066341a53733046894bd75c72c99566db

It might be viable and useful to collect coverage from system headers in some systems.
This patch adds --system-headers-coverage option (disabled by default) to enable
collecting coverage from system headers.

[phosek]

LGTM

clang/lib/CodeGen/CoverageMappingGen.cpp

 #define COVMAP_V3
 
 static llvm::cl::opt<bool> EmptyLineCommentCoverage(
     "emptyline-comment-coverage",
     llvm::cl::desc("Emit emptylines and comment lines as skipped regions (only "
                    "disable it on test)"),
     llvm::cl::init(true), llvm::cl::Hidden);
 
+static llvm::cl::opt<bool> SystemHeadersCoverage(
+    "system-headers-coverage",
+    llvm::cl::desc("Enable collecting coverage from system headers"),
+    llvm::cl::init(false), llvm::cl::Hidden);
+
 using namespace clang;
 using namespace CodeGen;
 using namespace llvm::coverage;
 
 CoverageSourceInfo *
 CoverageMappingModuleGen::setUpCoverageCallbacks(Preprocessor &PP) {
   CoverageSourceInfo *CoverageInfo =
       new CoverageSourceInfo(PP.getSourceManager());
void gatherFileIDs(SmallVectorImpl<unsigned> &Mapping) {
     llvm::SmallSet<FileID, 8> Visited;
     SmallVector<std::pair<SourceLocation, unsigned>, 8> FileLocs;
     for (const auto &Region : SourceRegions) {
       SourceLocation Loc = Region.getBeginLoc();
       FileID File = SM.getFileID(Loc);
       if (!Visited.insert(File).second)
         continue;
 
-      // Do not map FileID's associated with system headers.
-      if (SM.isInSystemHeader(SM.getSpellingLoc(Loc)))
+      // Do not map FileID's associated with system headers unless collecting
+      // coverage from system headers is explicitly enabled.
+      if (!SystemHeadersCoverage && SM.isInSystemHeader(SM.getSpellingLoc(Loc)))
         continue;
 
       unsigned Depth = 0;
       for (SourceLocation Parent = getIncludeOrExpansionLoc(Loc);
            Parent.isValid(); Parent = getIncludeOrExpansionLoc(Parent))
         ++Depth;
       FileLocs.push_back(std::make_pair(Loc, Depth));
     }
public:
   /// source regions.
   void emitSourceRegions(const SourceRegionFilter &Filter) {
     for (const auto &Region : SourceRegions) {
       assert(Region.hasEndLoc() && "incomplete region");
 
       SourceLocation LocStart = Region.getBeginLoc();
       assert(SM.getFileID(LocStart).isValid() && "region in invalid file");
 
-      // Ignore regions from system headers.
-      if (SM.isInSystemHeader(SM.getSpellingLoc(LocStart)))
+      // Ignore regions from system headers unless collecting coverage from
+      // system headers is explicitly enabled.
+      if (!SystemHeadersCoverage &&
+          SM.isInSystemHeader(SM.getSpellingLoc(LocStart)))
         continue;
 
       auto CovFileID = getCoverageFileID(LocStart);
       // Ignore regions that don't have a file, such as builtin macros.
       if (!CovFileID)
         continue;
 
       SourceLocation LocEnd = Region.getEndLoc();
void VisitStmt(const Stmt *S) {
     if (SaveTerminateStmt)
       HasTerminateStmt = true;
     handleFileExit(getEnd(S));
   }
 
   void VisitDecl(const Decl *D) {
     Stmt *Body = D->getBody();
 
-    // Do not propagate region counts into system headers.
-    if (Body && SM.isInSystemHeader(SM.getSpellingLoc(getStart(Body))))
+    // Do not propagate region counts into system headers unless collecting
+    // coverage from system headers is explicitly enabled.
+    if (!SystemHeadersCoverage && Body &&
+        SM.isInSystemHeader(SM.getSpellingLoc(getStart(Body))))
       return;
 
     // Do not visit the artificial children nodes of defaulted methods. The
     // lexer may not be able to report back precise token end locations for
     // these children nodes (llvm.org/PR39822), and moreover users will not be
     // able to see coverage for them.
     bool Defaulted = false;
     if (auto *Method = dyn_cast<CXXMethodDecl>(D))

clang/test/CoverageMapping/system_macro.cpp

-// RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -std=c++11 -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -main-file-name system_macro.cpp -o - %s | FileCheck %s
+// RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -mllvm -system-headers-coverage -std=c++11 -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -main-file-name system_macro.cpp -o - %s | FileCheck %s
 
 #ifdef IS_SYSHEADER
 
 #pragma clang system_header
 #define Func(x) if (x) {}
 #define SomeType int
 
 #else
 
 #define IS_SYSHEADER
 #include __FILE__
 
 // CHECK-LABEL: doSomething
 void doSomething(int x) { // CHECK: File 0, [[@LINE]]:25 -> {{[0-9:]+}} = #0
-  Func(x);
+  Func(x); // CHECK: Expansion,File 0, [[@LINE]]:3 -> [[@LINE]]:7
   return;
+  // CHECK: Expansion,File 0, [[@LINE+1]]:3 -> [[@LINE+1]]:11
   SomeType *f; // CHECK: File 0, [[@LINE]]:11 -> {{[0-9:]+}} = 0
 }
 
 // CHECK-LABEL: main
 int main() { // CHECK: File 0, [[@LINE]]:12 -> [[@LINE+2]]:2 = #0
   Func([] { return true; }());
 }
 
 #endif