Stack protector + coroutines + c++ exceptions causing musttail call must precede a ret with an optional bitcast

[lanza]

Bugzilla Link	50161
Resolution	FIXED
Resolved on	May 06, 2021 17:08
Version	trunk
OS	All
Blocks	#48661
CC	@tstellar
Fixed by commit(s)	5e3d9fc 471a386

Extended Description

As the title said, we (Facebook) were hitting an assert with coroutines, stack protector and c++ exceptions generating a musttail call that didn't immediately precede a ret. I fixed it by cherrypicking the below:

5e3d9fc

I could run creduce and generate a simple example if need be, but the diff's contents and it's description are pretty clear and the pick is clean.

[lanza]

assigned to @tstellar

[lanza]

Tim Northover was the author of the fix in 5e3d9fc

[tstellar]

Hi Tim,

What is your opinion on backporting this?

https://reviews.llvm.org/rG5e3d9fcc3a8802cea5b850a3ca40c515d916bf82

[TNorthover]

I'd say it's probably OK, though I'm not really an SSP expert. I had no idea anyone but Swift was hitting this.

[tstellar]

Merged: 471a386