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Re: [RFC PATCH v2] target/ppc: Enable hardfloat for PPC

From: Peter Maydell
Subject: Re: [RFC PATCH v2] target/ppc: Enable hardfloat for PPC
Date: Fri, 21 Feb 2020 16:11:01 +0000

On Fri, 21 Feb 2020 at 16:05, BALATON Zoltan <address@hidden> wrote:
> On Thu, 20 Feb 2020, Richard Henderson wrote:
> > On 2/18/20 9:10 AM, BALATON Zoltan wrote:
> >> +    DEFINE_PROP_BOOL("hardfloat", PowerPCCPU, hardfloat, true),
> >
> > I would also prefer a different name here -- perhaps x-no-fp-fi.
> What's wrong with hardfloat? That's how the code refers to this so if
> anyone searches what it does would turn up some meaningful results.

This prompted me to check what you're using the property for.
The cover letter says:
> This patch implements a simple way to keep the inexact flag set for
> hardfloat while still allowing to revert to softfloat for workloads
> that need more accurate albeit slower emulation. (Set hardfloat
> property of CPU, i.e. -cpu name,hardfloat=false for that.)

I think that is the wrong approach. Enabling use of the host
FPU should not affect the accuracy of the emulation, which
should remain bitwise-correct. We should only be using the
host FPU to the extent that we can do that without discarding
accuracy. As far as I'm aware that's how the hardfloat support
for other guest CPUs that use it works.

-- PMM

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