[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.

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

llvm-svn: 289920

1 files changed, 19 insertions, 4 deletions

diff --git a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
index 8ec08c9a872..b47628dde28 100644
--- a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
+++ b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
@@ -978,12 +978,16 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadata(bool ModuleLevel) {
           DIGlobalVariable,
           (Context, getMDOrNull(Record[1]), getMDString(Record[2]),
            getMDString(Record[3]), getMDOrNull(Record[4]), Record[5],
-           getDITypeRefOrNull(Record[6]), Record[7], Record[8], Expr,
+           getDITypeRefOrNull(Record[6]), Record[7], Record[8],
            getMDOrNull(Record[10]), AlignInBits));
-      MetadataList.assignValue(DGV, NextMetadataNo++);
 
-      if (Attach)
-        Attach->addDebugInfo(DGV);
+      if (Expr || Attach) {
+        auto *DGVE = DIGlobalVariableExpression::getDistinct(Context, DGV, Expr);
+        MetadataList.assignValue(DGVE, NextMetadataNo++);
+        if (Attach)
+          Attach->addDebugInfo(DGVE);
+      } else
+        MetadataList.assignValue(DGV, NextMetadataNo++);
 
       break;
     }
@@ -1033,6 +1037,17 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadata(bool ModuleLevel) {
           NextMetadataNo++);
       break;
     }
+    case bitc::METADATA_GLOBAL_VAR_EXPR: {
+      if (Record.size() != 3)
+        return error("Invalid record");
+
+      IsDistinct = Record[0];
+      MetadataList.assignValue(GET_OR_DISTINCT(DIGlobalVariableExpression,
+                                               (Context, getMDOrNull(Record[1]),
+                                                getMDOrNull(Record[2]))),
+                               NextMetadataNo++);
+      break;
+    }
     case bitc::METADATA_OBJC_PROPERTY: {
       if (Record.size() != 8)
         return error("Invalid record");