I think this is related to column information. ClusterFuzz wanted column information in addition to line info in stack traces, and Microsoft explained how to add this information to the line table, so we added it. Microsoft never turned column info on in their own compiler because they didn't like the debugger user experience, which is what I think you're seeing.

Will momentarily be addressed by turning off column info by default for CodeView debug info (with an option to enable it which is useful for sanitizer builds).

Visual Studio really wants column ranges if there's any column info.  With only the partial column info that Clang records, the highlights are wonky.  I tried various ways of synthesizing a range, but all had drawbacks, so it's best to omit the column info altogether.

https://reviews.llvm.org/rL279765

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a033f395bf2547cf4764f77cc9c86d08f3e22c23

commit a033f395bf2547cf4764f77cc9c86d08f3e22c23
Author: thakis <thakis@chromium.org>
Date: Wed Aug 31 05:16:14 2016

Roll clang 278861:280106.

* win: Members of base classes now should show up in debugger.
* win: Debugger shouldn't show funny highlights anymore due to
  debug info no longer including column information.  (we still
  force this on if sanitizers are used, mostly for clusterfuzz.
  maybe we want to make this toggleable independent of sanitizers
  at some point)
* win: -Wextern-initializer no longer warns on midl-generated code
* win: clang-cl now accepts /source-encoding:utf-8 and friends
  (utf-8 was the source enconding in clang-cl before already, but
  now we don't warn on an explicit flag requesting this)
* all platforms: Three plugin checks are now on-by-default,
  remove flags for these (see
    https://codereview.chromium.org/2267713003
    https://codereview.chromium.org/2268203002
    https://codereview.chromium.org/2265093002
  )
* win: clang-cl's /Brepro now does what it's supposed to do
* win: clang-cl now emits absolute paths in diagnostics, by
  popular request.

Ran `tools/clang/scripts/upload_revision.py 280106`.

BUG= 640254 , 637456 , 636109 , 636091 , 636099 

Review-Url: https://codereview.chromium.org/2292173002
Cr-Commit-Position: refs/heads/master@{#415563}

[modify] https://crrev.com/a033f395bf2547cf4764f77cc9c86d08f3e22c23/build/config/clang/BUILD.gn
[modify] https://crrev.com/a033f395bf2547cf4764f77cc9c86d08f3e22c23/build/config/compiler/BUILD.gn
[modify] https://crrev.com/a033f395bf2547cf4764f77cc9c86d08f3e22c23/build/config/sanitizers/BUILD.gn
[modify] https://crrev.com/a033f395bf2547cf4764f77cc9c86d08f3e22c23/build/config/win/BUILD.gn
[modify] https://crrev.com/a033f395bf2547cf4764f77cc9c86d08f3e22c23/tools/clang/scripts/update.py