[LLVMdev] Clarifying FMA-related TargetOptions

James Molloy James.Molloy at arm.com
Wed Feb 8 10:49:29 PST 2012

On that, I'm afraid I have no clue. Hopefully someone more knowledgeable than me will chip in.


From: Owen Anderson [resistor at mac.com]
Sent: 08 February 2012 18:48
To: James Molloy
Cc: List
Subject: Re: [LLVMdev] Clarifying FMA-related TargetOptions

On Feb 8, 2012, at 10:44 AM, James Molloy wrote:

> Hi Owen,
> Having looked into this due to Clang failing PlumHall with it recently I can give an opinion...
> I think !NoExcessFPPrecision covers FMA completely. There are indeed some algorithms which give incorrect results when FMA is enabled, examples being those that do floating point comparisons such as: a * b + c - d. If c == d, it is still possible for that result not to equal a*b, as "+c " will have been fused with the multiply whereas "- d" won't.

I agree that !NoExcessFPPrecision seems like it should cover FMA, but if that that is the case, what does LessPreciseFPMADOption cover?


-- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium.  Thank you.

More information about the llvm-dev mailing list