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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206507 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 95 insertions, 11 deletions

diff --git a/include/llvm/IR/Module.h b/include/llvm/IR/Module.h
index f728b4eeaa..3951355c86 100644
--- a/include/llvm/IR/Module.h
+++ b/include/llvm/IR/Module.h
@@ -598,6 +598,14 @@ public:
   /// is delete'd for real.  Note that no operations are valid on an object
   /// that has "dropped all references", except operator delete.
   void dropAllReferences();
+
+/// @}
+/// @name Utility functions for querying Debug information.
+/// @{
+
+  /// \brief Returns the Dwarf Version by checking module flags.
+  unsigned getDwarfVersion() const;
+
 /// @}
 };
 
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index d5c8a0a7b8..3b32639b68 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/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/lib/IR/Module.cpp b/lib/IR/Module.cpp
index 43f42bcf87..5dbed69ca6 100644
--- a/lib/IR/Module.cpp
+++ b/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/lib/Transforms/Utils/AddDiscriminators.cpp b/lib/Transforms/Utils/AddDiscriminators.cpp
index f42635e335..a4d813871e 100644
--- a/lib/Transforms/Utils/AddDiscriminators.cpp
+++ b/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();
diff --git a/test/Transforms/AddDiscriminators/no-discriminators.ll b/test/Transforms/AddDiscriminators/no-discriminators.ll
new file mode 100644
index 0000000000..f7b45e2955
--- /dev/null
+++ b/test/Transforms/AddDiscriminators/no-discriminators.ll
@@ -0,0 +1,71 @@
+; RUN: opt < %s -add-discriminators -S | FileCheck %s
+
+; We should not generate discriminators for DWARF versions prior to 4.
+;
+; Original code:
+;
+; int foo(long i) {
+;   if (i < 5) return 2; else return 90;
+; }
+;
+; None of the !dbg nodes associated with the if() statement should be
+; altered. If they are, it means that the discriminators pass added a
+; new lexical scope.
+
+define i32 @foo(i64 %i) #0 {
+entry:
+  %retval = alloca i32, align 4
+  %i.addr = alloca i64, align 8
+  store i64 %i, i64* %i.addr, align 8
+  call void @llvm.dbg.declare(metadata !{i64* %i.addr}, metadata !13), !dbg !14
+  %0 = load i64* %i.addr, align 8, !dbg !15
+; CHECK:  %0 = load i64* %i.addr, align 8, !dbg !15
+  %cmp = icmp slt i64 %0, 5, !dbg !15
+; CHECK:  %cmp = icmp slt i64 %0, 5, !dbg !15
+  br i1 %cmp, label %if.then, label %if.else, !dbg !15
+; CHECK:  br i1 %cmp, label %if.then, label %if.else, !dbg !15
+
+if.then:                                          ; preds = %entry
+  store i32 2, i32* %retval, !dbg !15
+  br label %return, !dbg !15
+
+if.else:                                          ; preds = %entry
+  store i32 90, i32* %retval, !dbg !15
+  br label %return, !dbg !15
+
+return:                                           ; preds = %if.else, %if.then
+  %1 = load i32* %retval, !dbg !17
+  ret i32 %1, !dbg !17
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!10, !11}
+!llvm.ident = !{!12}
+
+!0 = metadata !{i32 786449, metadata !1, i32 12, metadata !"clang version 3.5.0 ", i1 false, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !"", i32 1} ; [ DW_TAG_compile_unit ] [./no-discriminators] [DW_LANG_C99]
+!1 = metadata !{metadata !"no-discriminators", metadata !"."}
+!2 = metadata !{}
+!3 = metadata !{metadata !4}
+!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"foo", metadata !"foo", metadata !"", i32 1, metadata !6, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i64)* @foo, null, null, metadata !2, i32 1} ; [ DW_TAG_subprogram ] [line 1] [def] [foo]
+!5 = metadata !{i32 786473, metadata !1}          ; [ DW_TAG_file_type ] [./no-discriminators]
+!6 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !7, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{metadata !8, metadata !9}
+!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!9 = metadata !{i32 786468, null, null, metadata !"long int", i32 0, i64 64, i64 64, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [long int] [line 0, size 64, align 64, offset 0, enc DW_ATE_signed]
+!10 = metadata !{i32 2, metadata !"Dwarf Version", i32 2}
+; CHECK: !10 = metadata !{i32 2, metadata !"Dwarf Version", i32 2}
+!11 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
+!12 = metadata !{metadata !"clang version 3.5.0 "}
+!13 = metadata !{i32 786689, metadata !4, metadata !"i", metadata !5, i32 16777217, metadata !9, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [i] [line 1]
+!14 = metadata !{i32 1, i32 0, metadata !4, null}
+!15 = metadata !{i32 2, i32 0, metadata !16, null}
+; CHECK: !15 = metadata !{i32 2, i32 0, metadata !16, null}
+!16 = metadata !{i32 786443, metadata !1, metadata !4, i32 2, i32 0, i32 0, i32 0} ; [ DW_TAG_lexical_block ] [./no-discriminators]
+; CHECK: !16 = metadata !{i32 786443, metadata !1, metadata !4, i32 2, i32 0, i32 0, i32 0} ; [ DW_TAG_lexical_block ] [./no-discriminators]
+!17 = metadata !{i32 3, i32 0, metadata !4, null}