[windows] The VS compiler optimizes out fieldFromInstruction in Release builds when LLVM_ENABLE_ASSERTIONS is set to OFF

[Quuxplusone]

Bugzilla Link	PR38292
Status	NEW
Importance	P enhancement
Reported by	Stella Stamenova (stilis@microsoft.com)
Reported on	2018-07-24 15:31:08 -0700
Last modified on	2018-07-25 08:08:40 -0700
Version	trunk
Hardware	PC Windows NT
CC	dblaikie@gmail.com, llvm-bugs@lists.llvm.org
Fixed by commit(s)
Attachments
Blocks
Blocked by
See also

The VS compiler (on Windows) has a bug which results in fieldFromInstruction
being optimized out in some circumstances. This only happens in *release no
debug info* builds that have assertions *turned off* - in all other situations
the function is not inlined, so the functionality is correct.

All of the bots have assertions turned on, so this path is not regularly tested.

The workaround is to not inline the function on Windows - if the bug is fixed
in a later release of the VS compiler, the noinline specification can be
removed.

The test that consistently reproduces this is Lanai v11.txt test.

This bug is to track the workaround in FixedLenDecoderEmitter.cpp (and it's
potential future removal).

[Quuxplusone]

See https://reviews.llvm.org/D49753 for the code change