SuccessChanges

Summary

  1. [CGDebugInfo] Emit subprograms for decls when AT_tail_call is understood (details)
Commit a5c8ec4baa2c00d8dbca36ffd236a40f9e0c07ed by Vedant Kumar
[CGDebugInfo] Emit subprograms for decls when AT_tail_call is understood
Currently, clang emits subprograms for declared functions when the
target debugger or DWARF standard is known to support entry values
(DW_OP_entry_value & the GNU equivalent).
Treat DW_AT_tail_call the same way to allow debuggers to follow cross-TU
tail calls.
Pre-patch debug session with a cross-TU tail call:
```
* frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
   frame #1: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```
Post-patch (note that the tail-calling frame, "helper", is visible):
```
* frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
   frame #1: 0x0000000100000f80 main`helper [opt] [artificial]
   frame #2: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```
rdar://46577651
Differential Revision: https://reviews.llvm.org/D69743
The file was modifiedllvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
The file was modifiedclang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
The file was modifiedclang/test/CodeGen/debug-info-extern-call.c
The file was modifiedclang/lib/CodeGen/CGDebugInfo.cpp