https://build.chromium.org/p/chromium.fyi/builders/ClangToTWin%28dbg%29%20tester/builds/1845: clang r262348
https://build.chromium.org/p/chromium.fyi/builders/ClangToTWin%28dbg%29%20tester/builds/1846 corresponds to https://build.chromium.org/p/chromium.fyi/builders/ClangToTWin%28dbg%29/builds/4859: clang r262374

From `svn log -r r262348:r262374  https://nico@llvm.org/svn/llvm-project`, I'd guess this is

r262370 | majnemer | 2016-03-01 11:20:23 -0800 (Tue, 01 Mar 2016) | 12 lines

[X86] Elide references to _chkstk for dynamic allocas

The _chkstk function is called by the compiler to probe the stack in an
order consistent with Windows' expectations.  However, it is possible to
elide the call to _chkstk and manually adjust the stack pointer if we
can prove that the allocation is fixed size and smaller than the probe
size.

This shrinks chrome.dll, chrome_child.dll and chrome.exe by a
cummulative ~133 KB.



Alternatively, 

r262352 | hans | 2016-03-01 09:45:23 -0800 (Tue, 01 Mar 2016) | 9 lines

[X86] Check that attribute parameters match for tail calls (PR26590)

In the code below on 32-bit targets, x would previously get forwarded to g()
without sign-extension to 32 bits as required by the parameter attribute.

  void g(signed short);
  void f(unsigned short x) {
    g(x);
  }


looks somewhat in the vicinity too.


Please take a look!