Debug Info: support for DW_FORM_ref_addr.

To support ref_addr, we calculate the section offset of a DIE (i.e. offset
of a DIE from beginning of the debug info section). The Offset field in DIE
is currently CU-relative. To calculate the section offset, we add a
DebugInfoOffset field in CompileUnit to store the offset of a CU from beginning
of the debug info section. We set the value in DwarfUnits::computeSizeAndOffset
for each CompileUnit.

A helper function DIE::getCompileUnit is added to return the CU DIE that
the input DIE belongs to. We also add a map CUDieMap in DwarfDebug to help
finding the CU for a given CU DIE.

For a cross-referenced DIE, we first find the CU DIE it belongs to with
getCompileUnit, then we use CUDieMap to get the corresponding CU for the CU DIE.
Adding the section offset of the CU with the CU-relative offset of a DIE gives
us the seciton offset of the DIE.

We correctly emit ref_addr with relocation using EmitLabelPlusOffset when
doesDwarfUseRelocationsAcrossSections is true.

This commit handles the emission of DW_FORM_ref_addr when we have an attribute
with FORM_ref_addr. A follow-on patch will start using ref_addr when adding a
DIEEntry. This commit will be tested and verified in the follow-on patch.

Reviewed off-list by Eric, Thanks.

llvm-svn: 193658

llvm/lib/CodeGen/AsmPrinter/DIE.cpp

@@ -112,6 +112,18 @@ DIE::~DIE() {
     delete Children[i];
 }
 
+/// Climb up the parent chain to get the compile unit DIE to which this DIE
+/// belongs.
+const DIE *DIE::getCompileUnit() const {
+  const DIE *p = this;
+  while (p) {
+    if (p->getTag() == dwarf::DW_TAG_compile_unit)
+      return p;
+    p = p->getParent();
+  }
+  llvm_unreachable("We should not have orphaned DIEs.");
+}
+
 DIEValue *DIE::findAttribute(uint16_t Attribute) {
   const SmallVectorImpl<DIEValue *> &Values = getValues();
   const DIEAbbrev &Abbrevs = getAbbrev();

llvm/lib/CodeGen/AsmPrinter/DIE.h

@@ -146,6 +146,9 @@ namespace llvm {
     const std::vector<DIE *> &getChildren() const { return Children; }
     const SmallVectorImpl<DIEValue*> &getValues() const { return Values; }
     DIE *getParent() const { return Parent; }
+    /// Climb up the parent chain to get the compile unit DIE this DIE belongs
+    /// to.
+    const DIE *getCompileUnit() const;
     void setOffset(unsigned O) { Offset = O; }
     void setSize(unsigned S) { Size = S; }
 

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -33,7 +33,8 @@ using namespace llvm;
 /// CompileUnit - Compile unit constructor.
 CompileUnit::CompileUnit(unsigned UID, DIE *D, const MDNode *N, AsmPrinter *A,
                          DwarfDebug *DW, DwarfUnits *DWU)
-    : UniqueID(UID), Node(N), CUDie(D), Asm(A), DD(DW), DU(DWU), IndexTyDie(0) {
+    : UniqueID(UID), Node(N), CUDie(D), Asm(A), DD(DW), DU(DWU), IndexTyDie(0),
+      DebugInfoOffset(0) {
   DIEIntegerOne = new (DIEValueAllocator) DIEInteger(1);
   insertDIE(N, D);
 }

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

@@ -120,6 +120,9 @@ public:
     return AccelTypes;
   }
 
+  unsigned getDebugInfoOffset() const { return DebugInfoOffset; }
+  void setDebugInfoOffset(unsigned DbgInfoOff) { DebugInfoOffset = DbgInfoOff; }
+
   /// hasContent - Return true if this compile unit has something to write out.
   ///
   bool hasContent() const { return !CUDie->getChildren().empty(); }
@@ -347,6 +350,9 @@ private:
   /// getOrCreateStaticMemberDIE - Create new static data member DIE.
   DIE *getOrCreateStaticMemberDIE(DIDerivedType DT);
 
+  /// Offset of the CUDie from beginning of debug info section.
+  unsigned DebugInfoOffset;
+
   /// getLowerBoundDefault - Return the default lower bound for an array. If the
   /// DWARF version doesn't handle the language, return -1.
   int64_t getDefaultLowerBound() const;

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -821,6 +821,7 @@ CompileUnit *DwarfDebug::constructCompileUnit(const MDNode *N) {
   InfoHolder.addUnit(NewCU);
 
   CUMap.insert(std::make_pair(N, NewCU));
+  CUDieMap.insert(std::make_pair(Die, NewCU));
   return NewCU;
 }
 
@@ -1915,7 +1916,8 @@ void DwarfDebug::recordSourceLine(unsigned Line, unsigned Col, const MDNode *S,
 // Emit Methods
 //===----------------------------------------------------------------------===//
 
-// Compute the size and offset of a DIE.
+// Compute the size and offset of a DIE. The offset is relative to start of the
+// CU. It returns the offset after laying out the DIE.
 unsigned
 DwarfUnits::computeSizeAndOffset(DIE *Die, unsigned Offset) {
   // Get the children.
@@ -1960,16 +1962,26 @@ DwarfUnits::computeSizeAndOffset(DIE *Die, unsigned Offset) {
 
 // Compute the size and offset for each DIE.
 void DwarfUnits::computeSizeAndOffsets() {
+  // Offset from the first CU in the debug info section is 0 initially.
+  unsigned SecOffset = 0;
+
   // Iterate over each compile unit and set the size and offsets for each
   // DIE within each compile unit. All offsets are CU relative.
   for (SmallVectorImpl<CompileUnit *>::iterator I = CUs.begin(),
          E = CUs.end(); I != E; ++I) {
+    (*I)->setDebugInfoOffset(SecOffset);
+
+    // CU-relative offset is reset to 0 here.
     unsigned Offset =
       sizeof(int32_t) + // Length of Compilation Unit Info
       sizeof(int16_t) + // DWARF version number
       sizeof(int32_t) + // Offset Into Abbrev. Section
       sizeof(int8_t);   // Pointer Size (in bytes)
-    computeSizeAndOffset((*I)->getCUDie(), Offset);
+
+    // EndOffset here is CU-relative, after laying out
+    // all of the CU DIE.
+    unsigned EndOffset = computeSizeAndOffset((*I)->getCUDie(), Offset);
+    SecOffset += EndOffset;
   }
 }
 
@@ -2049,6 +2061,33 @@ void DwarfDebug::emitDIE(DIE *Die, std::vector<DIEAbbrev *> *Abbrevs) {
       Asm->OutStreamer.AddComment(dwarf::AttributeString(Attr));
 
     switch (Attr) {
+    case dwarf::DW_AT_abstract_origin:
+    case dwarf::DW_AT_type:
+    case dwarf::DW_AT_friend:
+    case dwarf::DW_AT_specification:
+    case dwarf::DW_AT_import:
+    case dwarf::DW_AT_containing_type: {
+      DIEEntry *E = cast<DIEEntry>(Values[i]);
+      DIE *Origin = E->getEntry();
+      unsigned Addr = Origin->getOffset();
+      if (Form == dwarf::DW_FORM_ref_addr) {
+        assert(!useSplitDwarf() && "TODO: dwo files can't have relocations.");
+        // For DW_FORM_ref_addr, output the offset from beginning of debug info
+        // section. Origin->getOffset() returns the offset from start of the
+        // compile unit.
+        CompileUnit *CU = CUDieMap.lookup(Origin->getCompileUnit());
+        assert(CU && "CUDie should belong to a CU.");
+        Addr += CU->getDebugInfoOffset();
+        if (Asm->MAI->doesDwarfUseRelocationsAcrossSections())
+          Asm->EmitLabelPlusOffset(DwarfInfoSectionSym, Addr,
+                                   DIEEntry::getRefAddrSize(Asm));
+        else
+          Asm->OutStreamer.EmitIntValue(Addr, DIEEntry::getRefAddrSize(Asm));
+      } else {
+        Asm->EmitInt32(Addr);
+      }
+      break;
+    }
     case dwarf::DW_AT_ranges: {
       // DW_AT_range Value encodes offset in debug_range section.
       DIEInteger *V = cast<DIEInteger>(Values[i]);

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -329,6 +329,9 @@ class DwarfDebug {
   // Maps subprogram MDNode with its corresponding CompileUnit.
   DenseMap <const MDNode *, CompileUnit *> SPMap;
 
+  // Maps a CU DIE with its corresponding CompileUnit.
+  DenseMap <const DIE *, CompileUnit *> CUDieMap;
+
   // Used to uniquely define abbreviations.
   FoldingSet<DIEAbbrev> AbbreviationsSet;