[LLVMdev] NEON vector instructions and the fast math IR flags

[Owen Anderson]

On Jun 6, 2013, at 8:35 PM, Tobias Grosser <grosser at google.com> wrote:

> I understand that some users do not require 754 compliant floating point behavior (clang on darwin?), which means they would probably not need this change. However, it should also not hurt them performance-wise as such users would probably set the relevant global fast-math flags to reduce the precision requirements, such that NEON instructions would be chosen anyway.

Darwin uses NEON for floating point, but does *not* (and should not). globally enable fast math flags.  Use of NEON for FP needs to remain achievable without globally setting the fast math flags.  Fast math may imply reasonably imply NEON, but the opposite direction is not accurate.

That said, I don't think anyone would object to making VFP codegen available under non-Darwin triples.  It's just a matter of making it happen.

-Owen