[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, 2 insertions, 2 deletions

diff --git a/llvm/test/Linker/only-needed-debug-metadata.ll b/llvm/test/Linker/only-needed-debug-metadata.ll
index 2d1949fb0ec..216c20cf732 100644
--- a/llvm/test/Linker/only-needed-debug-metadata.ll
+++ b/llvm/test/Linker/only-needed-debug-metadata.ll
@@ -38,8 +38,8 @@ define i32 @unused() !dbg !10 {
 !11 = !DISubroutineType(types: !12)
 !12 = !{!7}
 !13 = !{!14, !15}
-!14 = !DIGlobalVariable(name: "X", scope: !0, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true)
-!15 = !DIGlobalVariable(name: "U", scope: !0, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true)
+!14 = !DIGlobalVariableExpression(var: !DIGlobalVariable(name: "X", scope: !0, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true))
+!15 = !DIGlobalVariableExpression(var: !DIGlobalVariable(name: "U", scope: !0, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true))
 !16 = !{i32 2, !"Dwarf Version", i32 4}
 !17 = !{i32 2, !"Debug Info Version", i32 3}
 !18 = !{!"clang version 3.8.0 (trunk 251407) (llvm/trunk 251401)"}