[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, 10 insertions, 9 deletions

diff --git a/llvm/lib/IR/DIBuilder.cpp b/llvm/lib/IR/DIBuilder.cpp
index dfca6895590..d009322a572 100644
--- a/llvm/lib/IR/DIBuilder.cpp
+++ b/llvm/lib/IR/DIBuilder.cpp
@@ -532,29 +532,30 @@ static void checkGlobalVariableScope(DIScope *Context) {
 #endif
 }
 
-DIGlobalVariable *DIBuilder::createGlobalVariable(
+DIGlobalVariableExpression *DIBuilder::createGlobalVariableExpression(
     DIScope *Context, StringRef Name, StringRef LinkageName, DIFile *F,
-    unsigned LineNumber, DIType *Ty, bool isLocalToUnit,
-    DIExpression *Expr, MDNode *Decl, uint32_t AlignInBits) {
+    unsigned LineNumber, DIType *Ty, bool isLocalToUnit, DIExpression *Expr,
+    MDNode *Decl, uint32_t AlignInBits) {
   checkGlobalVariableScope(Context);
 
-  auto *N = DIGlobalVariable::getDistinct(
+  auto *GV = DIGlobalVariable::getDistinct(
       VMContext, cast_or_null<DIScope>(Context), Name, LinkageName, F,
-      LineNumber, Ty, isLocalToUnit, true, Expr,
-      cast_or_null<DIDerivedType>(Decl), AlignInBits);
+      LineNumber, Ty, isLocalToUnit, true, cast_or_null<DIDerivedType>(Decl),
+      AlignInBits);
+  auto *N = DIGlobalVariableExpression::get(VMContext, GV, Expr);
   AllGVs.push_back(N);
   return N;
 }
 
 DIGlobalVariable *DIBuilder::createTempGlobalVariableFwdDecl(
     DIScope *Context, StringRef Name, StringRef LinkageName, DIFile *F,
-    unsigned LineNumber, DIType *Ty, bool isLocalToUnit,
-    DIExpression *Expr, MDNode *Decl, uint32_t AlignInBits) {
+    unsigned LineNumber, DIType *Ty, bool isLocalToUnit, MDNode *Decl,
+    uint32_t AlignInBits) {
   checkGlobalVariableScope(Context);
 
   return DIGlobalVariable::getTemporary(
              VMContext, cast_or_null<DIScope>(Context), Name, LinkageName, F,
-             LineNumber, Ty, isLocalToUnit, false, Expr,
+             LineNumber, Ty, isLocalToUnit, false,
              cast_or_null<DIDerivedType>(Decl), AlignInBits)
       .release();
 }