Fix bug 19437 - Only add discriminators for DWARF 4 and above.

Summary:
This prevents the discriminator generation pass from triggering if
the DWARF version being used in the module is prior to 4.

Reviewers: echristo, dblaikie

CC: llvm-commits

Differential Revision: http://reviews.llvm.org/D3413

llvm-svn: 206507

3 files changed, 16 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index d5c8a0a..3b32639 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -168,14 +168,6 @@ DIType DbgVariable::getType() const {
 
 } // end llvm namespace
 
-/// Return Dwarf Version by checking module flags.
-static unsigned getDwarfVersionFromModule(const Module *M) {
-  Value *Val = M->getModuleFlag("Dwarf Version");
-  if (!Val)
-    return dwarf::DWARF_VERSION;
-  return cast<ConstantInt>(Val)->getZExtValue();
-}
-
 DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
     : Asm(A), MMI(Asm->MMI), FirstCU(0), PrevLabel(NULL), GlobalRangeCount(0),
       InfoHolder(A, "info_string", DIEValueAllocator),
@@ -211,7 +203,7 @@ DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
 
   DwarfVersion = DwarfVersionNumber
                      ? DwarfVersionNumber
-                     : getDwarfVersionFromModule(MMI->getModule());
+                     : MMI->getModule()->getDwarfVersion();
 
   {
     NamedRegionTimer T(DbgTimerName, DWARFGroupName, TimePassesIsEnabled);
diff --git a/llvm/lib/IR/Module.cpp b/llvm/lib/IR/Module.cpp
index 43f42bc..5dbed69c 100644
--- a/llvm/lib/IR/Module.cpp
+++ b/llvm/lib/IR/Module.cpp
@@ -23,6 +23,7 @@
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/LeakDetector.h"
+#include "llvm/Support/Dwarf.h"
 #include <algorithm>
 #include <cstdarg>
 #include <cstdlib>
@@ -429,3 +430,10 @@ void Module::dropAllReferences() {
   for(Module::alias_iterator I = alias_begin(), E = alias_end(); I != E; ++I)
     I->dropAllReferences();
 }
+
+unsigned Module::getDwarfVersion() const {
+  Value *Val = getModuleFlag("Dwarf Version");
+  if (!Val)
+    return dwarf::DWARF_VERSION;
+  return cast<ConstantInt>(Val)->getZExtValue();
+}
diff --git a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
index f42635e..a4d8138 100644
--- a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
+++ b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
@@ -154,10 +154,15 @@ static bool hasDebugInfo(const Function &F) {
 /// file and line location as I2. This new lexical block will have a
 /// different discriminator number than I1.
 bool AddDiscriminators::runOnFunction(Function &F) {
-  // No need to do anything if there is no debug info for this function.
   // If the function has debug information, but the user has disabled
   // discriminators, do nothing.
-  if (!hasDebugInfo(F) || NoDiscriminators) return false;
+  // Simlarly, if the function has no debug info, do nothing.
+  // Finally, if this module is built with dwarf versions earlier than 4,
+  // do nothing (discriminator support is a DWARF 4 feature).
+  if (NoDiscriminators ||
+      !hasDebugInfo(F) ||
+      F.getParent()->getDwarfVersion() < 4)
+    return false;
 
   bool Changed = false;
   Module *M = F.getParent();