[DebugInfo] Add DILabel metadata and intrinsic llvm.dbg.label.

In order to set breakpoints on labels and list source code around
labels, we need collect debug information for labels, i.e., label
name, the function label belong, line number in the file, and the
address label located. In order to keep these information in LLVM
IR and to allow backend to generate debug information correctly.
We create a new kind of metadata for labels, DILabel. The format
of DILabel is

!DILabel(scope: !1, name: "foo", file: !2, line: 3)

We hope to keep debug information as much as possible even the
code is optimized. So, we create a new kind of intrinsic for label
metadata to avoid the metadata is eliminated with basic block.
The intrinsic will keep existing if we keep it from optimized out.
The format of the intrinsic is

llvm.dbg.label(metadata !1)

It has only one argument, that is the DILabel metadata. The
intrinsic will follow the label immediately. Backend could get the
label metadata through the intrinsic's parameter.

We also create DIBuilder API for labels to be used by Frontend.
Frontend could use createLabel() to allocate DILabel objects, and use
insertLabel() to insert llvm.dbg.label intrinsic in LLVM IR.

Differential Revision: https://reviews.llvm.org/D45024

Patch by Hsiangkai Wang.

llvm-svn: 331841

1 files changed, 61 insertions, 6 deletions

diff --git a/llvm/lib/IR/DIBuilder.cpp b/llvm/lib/IR/DIBuilder.cpp
index 3e5ecdc2091..8596ebd9527 100644
--- a/llvm/lib/IR/DIBuilder.cpp
+++ b/llvm/lib/IR/DIBuilder.cpp
@@ -33,7 +33,7 @@ cl::opt<bool>
 
 DIBuilder::DIBuilder(Module &m, bool AllowUnresolvedNodes, DICompileUnit *CU)
   : M(m), VMContext(M.getContext()), CUNode(CU),
-      DeclareFn(nullptr), ValueFn(nullptr),
+      DeclareFn(nullptr), ValueFn(nullptr), LabelFn(nullptr),
       AllowUnresolvedNodes(AllowUnresolvedNodes) {}
 
 void DIBuilder::trackIfUnresolved(MDNode *N) {
@@ -47,18 +47,23 @@ void DIBuilder::trackIfUnresolved(MDNode *N) {
 }
 
 void DIBuilder::finalizeSubprogram(DISubprogram *SP) {
-  MDTuple *Temp = SP->getVariables().get();
+  MDTuple *Temp = SP->getRetainedNodes().get();
   if (!Temp || !Temp->isTemporary())
     return;
 
-  SmallVector<Metadata *, 4> Variables;
+  SmallVector<Metadata *, 16> RetainedNodes;
 
   auto PV = PreservedVariables.find(SP);
   if (PV != PreservedVariables.end())
-    Variables.append(PV->second.begin(), PV->second.end());
+    RetainedNodes.append(PV->second.begin(), PV->second.end());
 
-  DINodeArray AV = getOrCreateArray(Variables);
-  TempMDTuple(Temp)->replaceAllUsesWith(AV.get());
+  auto PL = PreservedLabels.find(SP);
+  if (PL != PreservedLabels.end())
+    RetainedNodes.append(PL->second.begin(), PL->second.end());
+
+  DINodeArray Node = getOrCreateArray(RetainedNodes);
+
+  TempMDTuple(Temp)->replaceAllUsesWith(Node.get());
 }
 
 void DIBuilder::finalize() {
@@ -699,6 +704,26 @@ DILocalVariable *DIBuilder::createParameterVariable(
                              /* AlignInBits */0);
 }
 
+DILabel *DIBuilder::createLabel(
+    DIScope *Scope, StringRef Name, DIFile *File,
+    unsigned LineNo, bool AlwaysPreserve) {
+  DIScope *Context = getNonCompileUnitScope(Scope);
+
+  auto *Node =
+      DILabel::get(VMContext, cast_or_null<DILocalScope>(Context), Name,
+                   File, LineNo);
+
+  if (AlwaysPreserve) {
+    /// The optimizer may remove labels. If there is an interest
+    /// to preserve label info in such situation then append it to
+    /// the list of retained nodes of the DISubprogram.
+    DISubprogram *Fn = getDISubprogram(Scope);
+    assert(Fn && "Missing subprogram for label");
+    PreservedLabels[Fn].emplace_back(Node);
+  }
+  return Node;
+}
+
 DIExpression *DIBuilder::createExpression(ArrayRef<uint64_t> Addr) {
   return DIExpression::get(VMContext, Addr);
 }
@@ -821,6 +846,18 @@ Instruction *DIBuilder::insertDeclare(Value *Storage, DILocalVariable *VarInfo,
   return insertDeclare(Storage, VarInfo, Expr, DL, InsertAtEnd, InsertBefore);
 }
 
+Instruction *DIBuilder::insertLabel(DILabel *LabelInfo, const DILocation *DL,
+                                    Instruction *InsertBefore) {
+  return insertLabel(
+      LabelInfo, DL, InsertBefore ? InsertBefore->getParent() : nullptr,
+      InsertBefore);
+}
+
+Instruction *DIBuilder::insertLabel(DILabel *LabelInfo, const DILocation *DL,
+                                    BasicBlock *InsertAtEnd) {
+  return insertLabel(LabelInfo, DL, InsertAtEnd, nullptr);
+}
+
 Instruction *DIBuilder::insertDbgValueIntrinsic(Value *V,
                                                 DILocalVariable *VarInfo,
                                                 DIExpression *Expr,
@@ -906,6 +943,24 @@ Instruction *DIBuilder::insertDbgValueIntrinsic(
   return B.CreateCall(ValueFn, Args);
 }
 
+Instruction *DIBuilder::insertLabel(
+    DILabel *LabelInfo, const DILocation *DL,
+    BasicBlock *InsertBB, Instruction *InsertBefore) {
+  assert(LabelInfo && "empty or invalid DILabel* passed to dbg.label");
+  assert(DL && "Expected debug loc");
+  assert(DL->getScope()->getSubprogram() ==
+             LabelInfo->getScope()->getSubprogram() &&
+         "Expected matching subprograms");
+  if (!LabelFn)
+    LabelFn = Intrinsic::getDeclaration(&M, Intrinsic::dbg_label);
+
+  trackIfUnresolved(LabelInfo);
+  Value *Args[] = {MetadataAsValue::get(VMContext, LabelInfo)};
+
+  IRBuilder<> B = getIRBForDbgInsertion(DL, InsertBB, InsertBefore);
+  return B.CreateCall(LabelFn, Args);
+}
+
 void DIBuilder::replaceVTableHolder(DICompositeType *&T,
                                     DIType *VTableHolder) {
   {