Re: [PATCH] MdePkg/DebugLib; swap if conditions in ASSERT_[EFI|RETURN]_ERROR

["Kinney, Michael D" <michael.d.kinney@intel.com>]

Ard,

I do not disagree with your logic.

The current algorithm is based on data from a long
time ago using what are now very old tool chains.

I will do some experiments on the currently supported
toolchains to see if the optimization is the same either
way.

I think the change you are suggesting is to improve 
performance for optimization disabled builds by removing
an extra call.  Is that correct?

Mike

> -----Original Message-----
> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
> Sent: Thursday, December 7, 2017 9:43 AM
> To: Kinney, Michael D <michael.d.kinney@intel.com>
> Cc: Alexei Fedorov <Alexei.Fedorov@arm.com>; edk2-
> devel@lists.01.org; Gao, Liming <liming.gao@intel.com>;
> Leif Lindholm <leif.lindholm@linaro.org>
> Subject: Re: [edk2] [PATCH] MdePkg/DebugLib; swap if
> conditions in ASSERT_[EFI|RETURN]_ERROR
> 
> On 7 December 2017 at 17:36, Kinney, Michael D
> <michael.d.kinney@intel.com> wrote:
> > Ard,
> >
> > With link time optimization, the current order produces
> > smaller code.
> >
> 
> I don't think it does. You are essentially saying that
> DebugAssertEnabled() may resolve to a link time constant
> FALSE under
> LTO.
> 
> In that case, why would the following two statement not
> be equivalent?
> 
> if (FALSE && EFI_ERROR (StatusParameter)) {}
> 
> if (EFI_ERROR (StatusParameter) && FALSE) {}
> 
> (which is essentially what a nested if () resolves to)
> 
> In other words, the compiler is smart enough to drop the
> status check
> in the second case, because it can see there are no side
> effects, and
> the condition can never be made true anyway.
> 
> > Without link time optimization, your patch will produce
> > smaller code, but not as small as link time optimized
> code.
> >