On 3/25/24 2:31 PM, Palmer Dabbelt wrote:
On Mon, 25 Mar 2024 13:27:34 PDT (-0700), Jeff Law wrote:
I'd doubt it's worth the complexity. Picking some reasonable value gets
you the vast majority of the benefit. Something like
COSTS_N_INSNS(6) is enough to get CSE to trigger. So what's left is a
reasonable cost, particularly for the division-by-constant case where we
need a ceiling for synth_mult.
Ya, makes sense. I noticed our multi-word multiply costs are a bit odd
too (they really only work for 64-bit mul on 32-bit targets), but that's
probably not worth worrying about either.
We do have a changes locally that adjust various costs. One of which is
highpart multiply. One of the many things to start working through once
gcc-15 opens for development. Hence my desire to help keep gcc-14 on
track for an on-time release.
Jeff
