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

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

Ard,

With link time optimization, the current order produces
smaller code.  

Without link time optimization, your patch will produce
smaller code, but not as small as link time optimized code.

Mike

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org]
> On Behalf Of Ard Biesheuvel
> Sent: Thursday, December 7, 2017 9:13 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 17:09, Ard Biesheuvel
> <ard.biesheuvel@linaro.org> wrote:
> > On 7 December 2017 at 17:01, Kinney, Michael D
> > <michael.d.kinney@intel.com> wrote:
> >> Ard,
> >>
> >> The reason for the current ordering is for size
> optimization.
> >>
> >> The most common implementation of DebugAssertEnabled()
> uses
> >> a FixedAtBuild PCD to determine if these are enabled.
> The
> >> check of status can be optimized away if they are
> disabled.
> >> If you reverse them, then the status check is always
> performed.
> >>
> >
> > DebugAssertEnabled() is a function call that gets
> resolved at link
> > time, and is not annotated as being free of side
> effects. So I agree
> > that the implementation of that function could be
> optimized into a
> > 'return true' or 'return false' depending on the
> compile time values
> > of those PCDs, but the way the macro is defined
> currently, it still
> > requires the function call to be made, and the
> conditional compare
> > with a constant that follows will still be present in
> the code.
> >
> > What I am suggesting is to replace it with a comparison
> with a
> > constant, and a conditional function call instead. This
> will not
> > affect code size, but will only remove needless
> function calls at
> > runtime.
> 
> Please refer to these threads for details:
> https://lists.01.org/pipermail/edk2-devel/2017-
> December/018790.html
> https://lists.01.org/pipermail/edk2-devel/2017-
> December/018809.html
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