[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, 1 insertions, 1 deletions

diff --git a/llvm/test/DebugInfo/X86/nondefault-subrange-array.ll b/llvm/test/DebugInfo/X86/nondefault-subrange-array.ll
index 9f1b2502d5a..3b734b9c901 100644
--- a/llvm/test/DebugInfo/X86/nondefault-subrange-array.ll
+++ b/llvm/test/DebugInfo/X86/nondefault-subrange-array.ll
@@ -33,7 +33,7 @@
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.3 (trunk 169136)", isOptimized: false, emissionKind: FullDebug, file: !20, enums: !1, retainedTypes: !1, globals: !3, imports:  !1)
 !1 = !{}
 !3 = !{!5}
-!5 = !DIGlobalVariable(name: "a", line: 1, isLocal: false, isDefinition: true, scope: null, file: !6, type: !7)
+!5 = !DIGlobalVariableExpression(var: !DIGlobalVariable(name: "a", line: 1, isLocal: false, isDefinition: true, scope: null, file: !6, type: !7))
 !6 = !DIFile(filename: "t.cpp", directory: "/Volumes/Sandbox/llvm")
 !7 = !DICompositeType(tag: DW_TAG_class_type, name: "A", line: 1, align: 32, file: !20, elements: !8)
 !8 = !{!9, !14}