[PATCH] D24815: [clang] make reciprocal estimate codegen a function attribute

[Mehdi AMINI via cfe-commits]

mehdi_amini added inline comments.


> spatel wrote in CGCall.cpp:1735
> Auto-upgrading is part of the solution. Based on how we've been doing this with vector intrinsics that get converted to IR, it's a ~3-step process:
> 
> 1. Prepare the backend (DAG) to handle the expected new IR patterns and add tests for those.
> 2. Auto-upgrade the IR, remove deprecated handling of the old IR patterns, and change/remove existing tests.
> 3. Update clang to not produce the deprecated patterns.
> 
> The extra step for FMF in the DAG is that we still don't allow FMF on all SDNode subclasses. The DAG plumbing for FMF only applies to binops because that's all that FMF on IR worked on at the time (fmul/fadd/fsub/fdiv/frem). Later, I added FMF to IR calls so we could have that functionality on sqrt, fma and other calls. Assuming that is ok (and I realize that it may be controversial), we can now extend FMF in the DAG to all SDNodes and have a full node-level FMF solution for the DAG layer.

I think I remember folks being against FMF on calls (Chris Lattner?), I'll try to find the relevant discussion.
Otherwise your plan seems fine to me!

https://reviews.llvm.org/D24815