On Fri, Jun 03, 2016 at 09:35:50AM +0100, James Greenhalgh wrote: > > Hi, > > This patch rebases the floating-point cost table for Cortex-A57 to be > relative to the cost of a floating-point move. This in response to this > feedback from Richard Sandiford [2] on Ramana's patch to calls.c [1] from > 2014: > > I think this is really a bug in the backend. The backend is assigning a > cost of COSTS_N_INSNS (3) to a floating-point constant not because the > constant itself is expensive -- it's actually as cheap as a register > in this context -- but because the backend considers floating-point > moves to be 3 times more expensive than cheap integer moves. > > The argument is that a move in mode X should be treated with cost > COSTS_N_INSNS (1), and other instructions should have a cost relative to > that move. For example, in this patch we say that instructions building a > floating-point constant are the same cost as a floating-point register to > register move. Fixing this fixes the issue Ramana was seeing, in a way > consistent with what other back-ends do. > > This patch gives a small improvement to Spec2000FP on a Cortex-A57 > platform. > > Bootstrapped on aarch64-none-linux-gnu with no issues. > > OK?
*ping* Thanks, James > 2016-06-03 James Greenhalgh <james.greenha...@arm.com> > > * config/arm/aarch-cost-tables.h (cortexa57_extra_costs): Make FP > costs relative to the cost of a register move. >
