[PATCH] D42898: Do not spill CSR to stack on entry to noreturn functions

[Francis Visoiu Mistrih via Phabricator via llvm-commits]

thegameg added a comment.

In https://reviews.llvm.org/D42898#999350, @kparzysz wrote:

> It could be a call to some library function (from a user-provided library).  I agree that this is a very unlikely scenario, but we've had a customer report a bug related to a similar situation.


Just out of curiosity, can you please share some more information about that?

>From what I understand,

A (nounwind) calls B (nounwind, noreturn)
B (nounwind, noreturn) calls library function C (nounwind?)
C (nounwind?) returns to A (nounwind) ?

In that case, B not saving the CSRs will destroy A's CSRs, but I can't really understand how we can end up in this case.

My assumptions are:

- can't (tail-)call throwing functions from `nounwind` functions
- can't (tail-)call returning functions from `noreturn` functions

but I might be wrong on that.


https://reviews.llvm.org/D42898