[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.

This reapplies r289902 with additional testcase upgrades and a change
to the Bitcode record for DIGlobalVariable, that makes upgrading the
old format unambiguous also for variables without DIExpressions.

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

llvm-svn: 290153

1 files changed, 17 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index cff2fd0c99c..8f23e31a79c 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -210,6 +210,9 @@ private:
                             SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
   void writeDIExpression(const DIExpression *N,
                          SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDIGlobalVariableExpression(const DIGlobalVariableExpression *N,
+                                       SmallVectorImpl<uint64_t> &Record,
+                                       unsigned Abbrev);
   void writeDIObjCProperty(const DIObjCProperty *N,
                            SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
   void writeDIImportedEntity(const DIImportedEntity *N,
@@ -1674,7 +1677,8 @@ void ModuleBitcodeWriter::writeDITemplateValueParameter(
 void ModuleBitcodeWriter::writeDIGlobalVariable(
     const DIGlobalVariable *N, SmallVectorImpl<uint64_t> &Record,
     unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  const uint64_t Version = 1 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | Version);
   Record.push_back(VE.getMetadataOrNullID(N->getScope()));
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
   Record.push_back(VE.getMetadataOrNullID(N->getRawLinkageName()));
@@ -1683,7 +1687,7 @@ void ModuleBitcodeWriter::writeDIGlobalVariable(
   Record.push_back(VE.getMetadataOrNullID(N->getType()));
   Record.push_back(N->isLocalToUnit());
   Record.push_back(N->isDefinition());
-  Record.push_back(VE.getMetadataOrNullID(N->getRawExpr()));
+  Record.push_back(/* expr */ 0);
   Record.push_back(VE.getMetadataOrNullID(N->getStaticDataMemberDeclaration()));
   Record.push_back(N->getAlignInBits());
 
@@ -1735,6 +1739,17 @@ void ModuleBitcodeWriter::writeDIExpression(const DIExpression *N,
   Record.clear();
 }
 
+void ModuleBitcodeWriter::writeDIGlobalVariableExpression(
+    const DIGlobalVariableExpression *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getVariable()));
+  Record.push_back(VE.getMetadataOrNullID(N->getExpression()));
+  
+  Stream.EmitRecord(bitc::METADATA_GLOBAL_VAR_EXPR, Record, Abbrev);
+  Record.clear();
+}
+
 void ModuleBitcodeWriter::writeDIObjCProperty(const DIObjCProperty *N,
                                               SmallVectorImpl<uint64_t> &Record,
                                               unsigned Abbrev) {