If the front end has emitted llvm.dbg.cu and other debug info anchors (clang does it now) then use them directly. This saves one scan of entire module, to collect debug info, which in turns saves few machine cycles at compile time.

llvm-svn: 130759

1 files changed, 49 insertions, 27 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 31b7bf2ae9f..3bff71daf5d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1113,44 +1113,66 @@ void DwarfDebug::beginModule(Module *M) {
   if (DisableDebugInfoPrinting)
     return;
 
-  DebugInfoFinder DbgFinder;
-  DbgFinder.processModule(*M);
-
   bool HasDebugInfo = false;
 
-  // Scan all the compile-units to see if there are any marked as the main unit.
-  // if not, we do not generate debug info.
-  for (DebugInfoFinder::iterator I = DbgFinder.compile_unit_begin(),
-       E = DbgFinder.compile_unit_end(); I != E; ++I) {
-    if (DICompileUnit(*I).isMain()) {
+  // If module has named metadata anchors then use them, otherwise scan the module
+  // using debug info finder to collect debug info.
+  NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
+  if (CU_Nodes) {
+    for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i) {
       HasDebugInfo = true;
-      break;
+      constructCompileUnit(CU_Nodes->getOperand(i));
     }
-  }
+    if (!HasDebugInfo)
+      return;
 
-  if (!HasDebugInfo) return;
+    if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.gv"))
+      for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
+        constructGlobalVariableDIE(NMD->getOperand(i));
+
+    if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.sp"))
+      for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
+        constructSubprogramDIE(NMD->getOperand(i));
+    
+  } else {
 
+    DebugInfoFinder DbgFinder;
+    DbgFinder.processModule(*M);
+    
+    // Scan all the compile-units to see if there are any marked as the main unit.
+    // if not, we do not generate debug info.
+    for (DebugInfoFinder::iterator I = DbgFinder.compile_unit_begin(),
+           E = DbgFinder.compile_unit_end(); I != E; ++I) {
+      if (DICompileUnit(*I).isMain()) {
+        HasDebugInfo = true;
+        break;
+      }
+    }
+    
+    // Create all the compile unit DIEs.
+    for (DebugInfoFinder::iterator I = DbgFinder.compile_unit_begin(),
+           E = DbgFinder.compile_unit_end(); I != E; ++I)
+      constructCompileUnit(*I);
+    
+    // Create DIEs for each global variable.
+    for (DebugInfoFinder::iterator I = DbgFinder.global_variable_begin(),
+           E = DbgFinder.global_variable_end(); I != E; ++I)
+      constructGlobalVariableDIE(*I);
+    
+    // Create DIEs for each subprogram.
+    for (DebugInfoFinder::iterator I = DbgFinder.subprogram_begin(),
+           E = DbgFinder.subprogram_end(); I != E; ++I)
+      constructSubprogramDIE(*I);
+  }
+  
+  if (!HasDebugInfo) return;
+  
   // Tell MMI that we have debug info.
   MMI->setDebugInfoAvailability(true);
-
+  
   // Emit initial sections.
   EmitSectionLabels();
 
-  // Create all the compile unit DIEs.
-  for (DebugInfoFinder::iterator I = DbgFinder.compile_unit_begin(),
-         E = DbgFinder.compile_unit_end(); I != E; ++I)
-    constructCompileUnit(*I);
-
-  // Create DIEs for each global variable.
-  for (DebugInfoFinder::iterator I = DbgFinder.global_variable_begin(),
-         E = DbgFinder.global_variable_end(); I != E; ++I)
-    constructGlobalVariableDIE(*I);
-
-  // Create DIEs for each subprogram.
-  for (DebugInfoFinder::iterator I = DbgFinder.subprogram_begin(),
-         E = DbgFinder.subprogram_end(); I != E; ++I)
-    constructSubprogramDIE(*I);
-
   //getOrCreateTypeDIE
   if (NamedMDNode *NMD = M->getNamedMetadata("llvm.dbg.enum"))
     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i) {