DebugInfo: New metadata representation for global variables.

This patch reverses the edge from DIGlobalVariable to GlobalVariable.
This will allow us to more easily preserve debug info metadata when
manipulating global variables.

Fixes PR30362. A program for upgrading test cases is attached to that
bug.

Differential Revision: http://reviews.llvm.org/D20147

llvm-svn: 281284

1 files changed, 24 insertions, 55 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 7822814c7a0..f9030d118e5 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -73,36 +73,9 @@ unsigned DwarfCompileUnit::getOrCreateSourceID(StringRef FileName,
       Asm->OutStreamer->hasRawTextSupport() ? 0 : getUniqueID());
 }
 
-// Return const expression if value is a GEP to access merged global
-// constant. e.g.
-// i8* getelementptr ({ i8, i8, i8, i8 }* @_MergedGlobals, i32 0, i32 0)
-static const ConstantExpr *getMergedGlobalExpr(const Value *V) {
-  const ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(V);
-  if (!CE || CE->getNumOperands() != 3 ||
-      CE->getOpcode() != Instruction::GetElementPtr)
-    return nullptr;
-
-  // First operand points to a global struct.
-  Value *Ptr = CE->getOperand(0);
-  GlobalValue *GV = dyn_cast<GlobalValue>(Ptr);
-  if (!GV || !isa<StructType>(GV->getValueType()))
-    return nullptr;
-
-  // Second operand is zero.
-  const ConstantInt *CI = dyn_cast_or_null<ConstantInt>(CE->getOperand(1));
-  if (!CI || !CI->isZero())
-    return nullptr;
-
-  // Third operand is offset.
-  if (!isa<ConstantInt>(CE->getOperand(2)))
-    return nullptr;
-
-  return CE;
-}
-
 /// getOrCreateGlobalVariableDIE - get or create global variable DIE.
 DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
-    const DIGlobalVariable *GV) {
+    const DIGlobalVariable *GV, const GlobalVariable *Global) {
   // Check for pre-existence.
   if (DIE *Die = getDIE(GV))
     return Die;
@@ -147,12 +120,22 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
 
   // Add location.
   bool addToAccelTable = false;
-  if (auto *Global = dyn_cast_or_null<GlobalVariable>(GV->getVariable())) {
+
+  DIExpression *Expr = GV->getExpr();
+
+  // For compatibility with DWARF 3 and earlier,
+  // DW_AT_location(DW_OP_constu, X, DW_OP_stack_value) becomes
+  // DW_AT_const_value(X).
+  if (Expr && Expr->getNumElements() == 3 &&
+      Expr->getElement(0) == dwarf::DW_OP_constu &&
+      Expr->getElement(2) == dwarf::DW_OP_stack_value) {
+    addConstantValue(*VariableDIE, /*Unsigned=*/true, Expr->getElement(1));
     // We cannot describe the location of dllimport'd variables: the computation
     // of their address requires loads from the IAT.
-    if (!Global->hasDLLImportStorageClass()) {
+  } else if (!Global || !Global->hasDLLImportStorageClass()) {
+    DIELoc *Loc = new (DIEValueAllocator) DIELoc;
+    if (Global) {
       addToAccelTable = true;
-      DIELoc *Loc = new (DIEValueAllocator) DIELoc;
       const MCSymbol *Sym = Asm->getSymbol(Global);
       if (Global->isThreadLocal()) {
         if (Asm->TM.Options.EmulatedTLS) {
@@ -187,30 +170,16 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
         addOpAddress(*Loc, Sym);
       }
 
-      addBlock(*VariableDIE, dwarf::DW_AT_location, Loc);
-      if (DD->useAllLinkageNames())
-        addLinkageName(*VariableDIE, GV->getLinkageName());
-    }
-  } else if (const ConstantInt *CI =
-                 dyn_cast_or_null<ConstantInt>(GV->getVariable())) {
-    addConstantValue(*VariableDIE, CI, GTy);
-  } else if (const ConstantExpr *CE = getMergedGlobalExpr(GV->getVariable())) {
-    auto *Ptr = cast<GlobalValue>(CE->getOperand(0));
-    if (!Ptr->hasDLLImportStorageClass()) {
-      addToAccelTable = true;
-      // GV is a merged global.
-      DIELoc *Loc = new (DIEValueAllocator) DIELoc;
-      MCSymbol *Sym = Asm->getSymbol(Ptr);
-      DD->addArangeLabel(SymbolCU(this, Sym));
-      addOpAddress(*Loc, Sym);
-      addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_constu);
-      SmallVector<Value *, 3> Idx(CE->op_begin() + 1, CE->op_end());
-      addUInt(*Loc, dwarf::DW_FORM_udata,
-              Asm->getDataLayout().getIndexedOffsetInType(Ptr->getValueType(),
-                                                          Idx));
-      addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_plus);
-      addBlock(*VariableDIE, dwarf::DW_AT_location, Loc);
+      if (Expr) {
+        DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
+        DwarfExpr.AddExpression(Expr->expr_op_begin(), Expr->expr_op_end());
+      }
     }
+
+    addBlock(*VariableDIE, dwarf::DW_AT_location, Loc);
+
+    if (DD->useAllLinkageNames())
+      addLinkageName(*VariableDIE, GV->getLinkageName());
   }
 
   if (addToAccelTable) {
@@ -674,7 +643,7 @@ DIE *DwarfCompileUnit::constructImportedEntityDIE(
   else if (auto *T = dyn_cast<DIType>(Entity))
     EntityDie = getOrCreateTypeDIE(T);
   else if (auto *GV = dyn_cast<DIGlobalVariable>(Entity))
-    EntityDie = getOrCreateGlobalVariableDIE(GV);
+    EntityDie = getOrCreateGlobalVariableDIE(GV, nullptr);
   else
     EntityDie = getDIE(Entity);
   assert(EntityDie);