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

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

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org]
> On Behalf Of Ard Biesheuvel
> Sent: Thursday, December 7, 2017 11:53 AM
> To: Kinney, Michael D <michael.d.kinney@intel.com>
> Cc: Alexei Fedorov <Alexei.Fedorov@arm.com>; edk2-
> devel@lists.01.org; Leif Lindholm
> <leif.lindholm@linaro.org>; Gao, Liming
> <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH] MdePkg/DebugLib; swap if
> conditions in ASSERT_[EFI|RETURN]_ERROR
> 
> On 7 December 2017 at 19:49, Kinney, Michael D
> <michael.d.kinney@intel.com> wrote:
> > 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.
> >
> 
> With LTO?

Yes.  The LTCG feature for VS tool chains.

> 
> > I will do some experiments on the currently supported
> > toolchains to see if the optimization is the same
> either
> > way.
> >
> 
> Thank you.
> 
> > I think the change you are suggesting is to improve
> > performance for optimization disabled builds by
> removing
> > an extra call.  Is that correct?
> >
> 
> Well, for DEBUG builds, yes. But given that the function
> call cannot
> be optimized away (on non-LTO builds), it affects
> optimized builds as
> well.

Do you mean compiler optimizations enabled, but linker
optimizations disabled.

> 
> --
> Ard.
> 
> 
> >> -----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.
> >> >
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