[IR] Remove the DIExpression field from DIGlobalVariable.

This patch implements PR31013 by introducing a
DIGlobalVariableExpression that holds a pair of DIGlobalVariable and
DIExpression.

Currently, DIGlobalVariables holds a DIExpression. This is not the
best way to model this:

(1) The DIGlobalVariable should describe the source level variable,
    not how to get to its location.

(2) It makes it unsafe/hard to update the expressions when we call
    replaceExpression on the DIGLobalVariable.

(3) It makes it impossible to represent a global variable that is in
    more than one location (e.g., a variable with multiple
    DW_OP_LLVM_fragment-s).  We also moved away from attaching the
    DIExpression to DILocalVariable for the same reasons.

<rdar://problem/29250149>
https://llvm.org/bugs/show_bug.cgi?id=31013
Differential Revision: https://reviews.llvm.org/D26769

llvm-svn: 289902

1 files changed, 36 insertions, 9 deletions

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index fe61c279778..75c397e1345 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -514,18 +514,17 @@ DIGlobalVariable *
 DIGlobalVariable::getImpl(LLVMContext &Context, Metadata *Scope, MDString *Name,
                           MDString *LinkageName, Metadata *File, unsigned Line,
                           Metadata *Type, bool IsLocalToUnit, bool IsDefinition,
-                          Metadata *Variable,
                           Metadata *StaticDataMemberDeclaration,
-                          uint32_t AlignInBits,
-                          StorageType Storage, bool ShouldCreate) {
+                          uint32_t AlignInBits, StorageType Storage,
+                          bool ShouldCreate) {
   assert(isCanonical(Name) && "Expected canonical MDString");
   assert(isCanonical(LinkageName) && "Expected canonical MDString");
   DEFINE_GETIMPL_LOOKUP(DIGlobalVariable,
                         (Scope, Name, LinkageName, File, Line, Type,
-                         IsLocalToUnit, IsDefinition, Variable,
+                         IsLocalToUnit, IsDefinition,
                          StaticDataMemberDeclaration, AlignInBits));
-  Metadata *Ops[] = {Scope, Name,        File,     Type,
-                     Name,  LinkageName, Variable, StaticDataMemberDeclaration};
+  Metadata *Ops[] = {
+      Scope, Name, File, Type, Name, LinkageName, StaticDataMemberDeclaration};
   DEFINE_GETIMPL_STORE(DIGlobalVariable,
                        (Line, IsLocalToUnit, IsDefinition, AlignInBits),
                        Ops);
@@ -581,10 +580,17 @@ bool DIExpression::isValid() const {
     default:
       return false;
     case dwarf::DW_OP_LLVM_fragment:
-    case dwarf::DW_OP_stack_value:
-      // We only support fragment and stack value expressions which appear at
-      // the end.
+      // A fragment operator must appear at the end.
       return I->get() + I->getSize() == E->get();
+    case dwarf::DW_OP_stack_value: {
+      // Must be the last one or followed by a DW_OP_LLVM_fragment.
+      if (I->get() + I->getSize() == E->get())
+        break;
+      auto J = I;
+      if ((++J)->getOp() != dwarf::DW_OP_LLVM_fragment)
+        return false;
+      break;
+    }
     case dwarf::DW_OP_constu:
     case dwarf::DW_OP_plus:
     case dwarf::DW_OP_minus:
@@ -613,6 +619,27 @@ uint64_t DIExpression::getFragmentSizeInBits() const {
   return getElement(getNumElements() - 1);
 }
 
+bool DIExpression::isConstant() const {
+  // Recognize DW_OP_constu C DW_OP_stack_value (DW_OP_LLVM_fragment Len Ofs)?.
+  if (getNumElements() != 3 && getNumElements() != 6)
+    return false;
+  if (getElement(0) != dwarf::DW_OP_constu ||
+      getElement(2) != dwarf::DW_OP_stack_value)
+    return false;
+  if (getNumElements() == 6 && getElement(3) != dwarf::DW_OP_LLVM_fragment)
+    return false;
+  return true;
+}
+
+DIGlobalVariableExpression *
+DIGlobalVariableExpression::getImpl(LLVMContext &Context, Metadata *Variable,
+                                    Metadata *Expression, StorageType Storage,
+                                    bool ShouldCreate) {
+  DEFINE_GETIMPL_LOOKUP(DIGlobalVariableExpression, (Variable, Expression));
+  Metadata *Ops[] = {Variable, Expression};
+  DEFINE_GETIMPL_STORE_NO_CONSTRUCTOR_ARGS(DIGlobalVariableExpression, Ops);
+}
+
 DIObjCProperty *DIObjCProperty::getImpl(
     LLVMContext &Context, MDString *Name, Metadata *File, unsigned Line,
     MDString *GetterName, MDString *SetterName, unsigned Attributes,