[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/CodeGen/X86/null-streamer.ll b/llvm/test/CodeGen/X86/null-streamer.ll
index b331b92868f..30dfade356b 100644
--- a/llvm/test/CodeGen/X86/null-streamer.ll
+++ b/llvm/test/CodeGen/X86/null-streamer.ll
@@ -22,6 +22,6 @@ define void @f1() {
 !7 = !{!8}
 !8 = !DIBasicType(tag: DW_TAG_base_type, size: 32, align: 32, encoding: DW_ATE_signed)
 !9 = !{!10}
-!10 = !DIGlobalVariable(name: "i", linkageName: "_ZL1i", line: 1, isLocal: true, isDefinition: true, scope: null, file: !1, type: !8)
+!10 = !DIGlobalVariableExpression(var: !DIGlobalVariable(name: "i", linkageName: "_ZL1i", line: 1, isLocal: true, isDefinition: true, scope: null, file: !1, type: !8))
 !11 = !{i32 2, !"Dwarf Version", i32 3}
 !13 = !{i32 1, !"Debug Info Version", i32 3}