From 2f1182c0aced623f09a4f4577cf1ff0f0656e460 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 5 May 2010 23:41:32 +0000
Subject: [PATCH] Emit debug info for MachineInstrs with unknown debug
 locations, instead of just letting them inherit the debug locations of
 adjacent instructions.

Debug info should aim to be either accurate or absent.

llvm-svn: 103135
---
 lib/CodeGen/AsmPrinter/DwarfDebug.cpp | 53 +++++++++++++++++----------
 1 file changed, 34 insertions(+), 19 deletions(-)

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index e9e9ba55db1..4da549866bf 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2150,8 +2150,20 @@ void DwarfDebug::collectVariableInfo() {
 void DwarfDebug::beginScope(const MachineInstr *MI) {
   // Check location.
   DebugLoc DL = MI->getDebugLoc();
-  if (DL.isUnknown())
+  if (DL.isUnknown()) {
+    // This instruction has no debug location. If the preceding instruction
+    // did, emit debug location information to indicate that the debug
+    // location is now unknown.
+    MCSymbol *Label = NULL;
+    if (DL == PrevInstLoc)
+      Label = PrevLabel;
+    else {
+      Label = recordSourceLine(DL.getLine(), DL.getCol(), 0);
+      PrevInstLoc = DL;
+      PrevLabel = Label;
+    }
     return;
+  }
 
   MDNode *Scope = DL.getScope(Asm->MF->getFunction()->getContext());
   
@@ -2564,23 +2576,28 @@ MCSymbol *DwarfDebug::recordSourceLine(unsigned Line, unsigned Col, MDNode *S) {
   StringRef Dir;
   StringRef Fn;
 
-  DIDescriptor Scope(S);
-  if (Scope.isCompileUnit()) {
-    DICompileUnit CU(S);
-    Dir = CU.getDirectory();
-    Fn = CU.getFilename();
-  } else if (Scope.isSubprogram()) {
-    DISubprogram SP(S);
-    Dir = SP.getDirectory();
-    Fn = SP.getFilename();
-  } else if (Scope.isLexicalBlock()) {
-    DILexicalBlock DB(S);
-    Dir = DB.getDirectory();
-    Fn = DB.getFilename();
-  } else
-    assert(0 && "Unexpected scope info");
+  unsigned Src = 1;
+  if (S) {
+    DIDescriptor Scope(S);
+
+    if (Scope.isCompileUnit()) {
+      DICompileUnit CU(S);
+      Dir = CU.getDirectory();
+      Fn = CU.getFilename();
+    } else if (Scope.isSubprogram()) {
+      DISubprogram SP(S);
+      Dir = SP.getDirectory();
+      Fn = SP.getFilename();
+    } else if (Scope.isLexicalBlock()) {
+      DILexicalBlock DB(S);
+      Dir = DB.getDirectory();
+      Fn = DB.getFilename();
+    } else
+      assert(0 && "Unexpected scope info");
+
+    Src = GetOrCreateSourceID(Dir, Fn);
+  }
 
-  unsigned Src = GetOrCreateSourceID(Dir, Fn);
   MCSymbol *Label = MMI->getContext().CreateTempSymbol();
   Lines.push_back(SrcLineInfo(Line, Col, Src, Label));
 
@@ -2967,8 +2984,6 @@ void DwarfDebug::emitDebugLines() {
       MCSymbol *Label = LineInfo.getLabel();
       if (!Label->isDefined()) continue; // Not emitted, in dead code.
 
-      if (LineInfo.getLine() == 0) continue;
-
       if (Asm->isVerbose()) {
         std::pair<unsigned, unsigned> SrcID =
           getSourceDirectoryAndFileIds(LineInfo.getSourceID());