function_coverage_fastcomp.diff

diff --git a/lib/Target/JSBackend/JSBackend.cpp b/lib/Target/JSBackend/JSBackend.cpp
index d1d83a4..bd0e6c4 100644
--- a/lib/Target/JSBackend/JSBackend.cpp
+++ b/lib/Target/JSBackend/JSBackend.cpp
@@ -152,6 +152,10 @@ WebAssembly("emscripten-wasm",
             cl::desc("Generate asm.js which will later be compiled to WebAssembly (see emscripten BINARYEN setting)"),
             cl::init(false));
 
+static cl::opt<bool>
+FunctionCoverage("function-coverage",
+            cl::desc("Injects coverage tracking into asm.js functions"),
+            cl::init(false));
 
 extern "C" void LLVMInitializeJSBackendTarget() {
   // Register the target.
@@ -2987,6 +2991,9 @@ void JSWriter::printFunctionBody(const Function *F) {
     }
   }
 
+  if (FunctionCoverage)
+    Out << "\n HEAP8[" << getGlobalAddress("func_cov") << ">>0] = 1|0;\n";
+
   // Emit (relooped) code
   char *buffer = Relooper::GetOutputBuffer();
   nl(Out) << buffer;
@@ -3142,6 +3149,21 @@ void JSWriter::printFunction(const Function *F) {
 }
 
 void JSWriter::printModuleBody() {
+  
+  if (FunctionCoverage) {
+      // Count functions
+      int function_count = 0;
+      for (Module::const_iterator II = TheModule->begin(), E = TheModule->end();
+          II != E; ++II) {
+          auto I = &*II;
+          if (!I->isDeclaration()) {
+              function_count++;
+          }
+      }
+
+      allocateZeroInitAddress("func_cov", 4, function_count);
+  }
+
   processConstants();
 
   if (Relocatable) {