[llvm-commits] LLVM patch to support ARM fused multiply add/subtract instructions

[James Molloy]

Hi Ana,

[Forwarding my review comments to this thread because I originally replied to the commit itself]

I'm not 100% happy with this patch. The implementation means that -mattr=+neon,+vfp4 does not enable neon-vfp4, which I think is rather confusing.

I'd much prefer the predicate to be rewritten such that hasNEONVFP4() === hasNEONVFP4 || (hasVFP4 && hasNEON), what do you think?

Cheers,

James

-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Anton Korobeynikov
Sent: 22 January 2012 12:12
To: Ana Pazos
Cc: rajav at codeaurora.org; llvm-commits at cs.uiuc.edu
Subject: Re: [llvm-commits] LLVM patch to support ARM fused multiply add/subtract instructions

Hi Ana,

Comitted as r148658.

> Some ARMv7-A processor implementations  (e.g, Qualcomm 8960, ARM Cortex-A5)
> support fused multiply add/subtract instructions (VFMA/VFMS) which have
> lower latency and greater accuracy than the chained multiply add/subtract
> instructions (VMLA/VMLS).
Just curious - what are the performance / accuracy wins for fma stuff here?

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

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