[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, 1 insertions, 1 deletions

diff --git a/llvm/test/DebugInfo/AArch64/bitfields.ll b/llvm/test/DebugInfo/AArch64/bitfields.ll
index 79a7b13e3e0..0adeb74ddce 100644
--- a/llvm/test/DebugInfo/AArch64/bitfields.ll
+++ b/llvm/test/DebugInfo/AArch64/bitfields.ll
@@ -58,7 +58,7 @@ target triple = "aarch64_be--linux-gnu"
 !1 = !DIFile(filename: "bitfields.c", directory: "/")
 !2 = !{}
 !3 = !{!4}
-!4 = !DIGlobalVariable(name: "b", scope: !0, file: !5, line: 8, type: !6, isLocal: false, isDefinition: true)
+!4 = !DIGlobalVariableExpression(var: !DIGlobalVariable(name: "b", scope: !0, file: !5, line: 8, type: !6, isLocal: false, isDefinition: true))
 !5 = !DIFile(filename: "bitfields.c", directory: "/")
 !6 = !DICompositeType(tag: DW_TAG_structure_type, name: "bitfield", file: !5, line: 1, size: 96, elements: !7)
 !7 = !{!8, !10, !11, !12}