[LLVM 4.0] Incomplete debuginfo for globals.

[TimNN]

Issue: gdb shows globals as <optimized out> when a rust program is compiled with llvm 4.0.

Test program:

static mut I64: i64 = -64;

 fn main() {
     _zzz();

     let _a = unsafe { I64 };
 }

 fn _zzz() {()}

Compiling with rust + LLVM 4.0 produces this IR, excerpts:

@_ZN5globt3I6417h1343cea697c2f8f6E = internal global i64 -64, align 8

!6 = !DIGlobalVariableExpression(var: !7)
!7 = distinct !DIGlobalVariable(name: "I64", linkageName: "_ZN5globt3I64E", scope: !8, file: !9, line: 1, type: !10, isLocal: true, isDefinition: true, align: 8)

From looking at the clang 4.0 output of a similar program, I have determined that the static definition (excerpt line 1) is missing a , !dbg !6. The addition of such a !dbg fixed the issue, as verified by manually editing the IR and compiling with llc.

cc @michaelwoerister, @dylanmckay

If someone can point me in the right direction, where / what functions should be called, I can try to fix this (I can also test any potential patches).

Edit: Also feel free to ping me on IRC.