[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, 1 deletions

diff --git a/llvm/test/DebugInfo/X86/stack-value-dwarf4.ll b/llvm/test/DebugInfo/X86/stack-value-dwarf4.ll
index ad2aeb2e6af..5f9213f3bdd 100644
--- a/llvm/test/DebugInfo/X86/stack-value-dwarf4.ll
+++ b/llvm/test/DebugInfo/X86/stack-value-dwarf4.ll
@@ -25,13 +25,14 @@ target triple = "x86_64-unknown-linux-gnu"
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang", file: !4, globals: !1, emissionKind: FullDebug)
 !1 = !{!2}
-!2 = distinct !DIGlobalVariable(name: "a", scope: null, isLocal: false, isDefinition: true, expr: !3, type: !5)
+!2 = !DIGlobalVariableExpression(var: !8, expr: !3)
 !3 = !DIExpression(DW_OP_constu, 4, DW_OP_constu, 4, DW_OP_stack_value)
 !4 = !DIFile(filename: "<stdin>", directory: "/")
 !5 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
 
 !6 = !{i32 2, !"Dwarf Version", i32 2}
 !7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DIGlobalVariable(name: "a", scope: null, isLocal: false, isDefinition: true, type: !5)
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!6, !7}