From e02e58528ae7e3c1d8115e88fdd60bb8f9b0dfdc Mon Sep 17 00:00:00 2001
From: Devang Patel <dpatel@apple.com>
Date: Tue, 3 May 2011 16:45:22 +0000
Subject: [PATCH] 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
---
 llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp | 76 ++++++++++++++--------
 1 file changed, 49 insertions(+), 27 deletions(-)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 31b7bf2ae9f1..3bff71daf5dc 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 (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) {