Pass to emit DWARF path discriminators.

DWARF discriminators are used to distinguish multiple control flow paths
on the same source location. When this happens, instructions across
basic block boundaries will share the same debug location.

This pass detects this situation and creates a new lexical scope to one
of the two instructions. This lexical scope is a child scope of the
original and contains a new discriminator value. This discriminator is
then picked up from MCObjectStreamer::EmitDwarfLocDirective to be
written on the object file.

This fixes http://llvm.org/bugs/show_bug.cgi?id=18270.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202752 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 24 insertions, 0 deletions

diff --git a/lib/IR/DebugInfo.cpp b/lib/IR/DebugInfo.cpp
index 749e0b5057..f5884a4a90 100644
--- a/lib/IR/DebugInfo.cpp
+++ b/lib/IR/DebugInfo.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
+#include "LLVMContextImpl.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Dwarf.h"
@@ -818,6 +819,29 @@ DIArray DICompileUnit::getImportedEntities() const {
   return DIArray(getNodeField(DbgNode, 11));
 }
 
+/// copyWithNewScope - Return a copy of this location, replacing the
+/// current scope with the given one.
+DILocation DILocation::copyWithNewScope(LLVMContext &Ctx,
+                                        DILexicalBlock NewScope) {
+  SmallVector<Value *, 10> Elts;
+  assert(Verify());
+  for (unsigned I = 0; I < DbgNode->getNumOperands(); ++I) {
+    if (I != 2)
+      Elts.push_back(DbgNode->getOperand(I));
+    else
+      Elts.push_back(NewScope);
+  }
+  MDNode *NewDIL = MDNode::get(Ctx, Elts);
+  return DILocation(NewDIL);
+}
+
+/// computeNewDiscriminator - Generate a new discriminator value for this
+/// file and line location.
+unsigned DILocation::computeNewDiscriminator(LLVMContext &Ctx) {
+  std::pair<const char *, unsigned> Key(getFilename().data(), getLineNumber());
+  return ++Ctx.pImpl->DiscriminatorTable[Key];
+}
+
 /// fixupSubprogramName - Replace contains special characters used
 /// in a typical Objective-C names with '.' in a given string.
 static void fixupSubprogramName(DISubprogram Fn, SmallVectorImpl<char> &Out) {