[fpc-pascal] with statement using mulltiple objects

Sven Barth pascaldragon at googlemail.com
Mon Sep 15 07:57:28 CEST 2014

On 15.09.2014 03:06, Jim Leonard wrote:
> On 9/13/2014 2:02 PM, Sven Barth wrote:
>> It has always worked in this manner. It's just for abbreviating typing,
>> not for combining properties. (and then the with-variant with multiple
>> elements is even more seldomly used than the single-element one...)
> In the Turbo Pascal days, WITH allowed for some user-directed compiler
> optimization.  From the TP7 manual:
> "In certain situations, Turbo Pascal's code generator can eliminate
> redundant pointer-load instructions, shrinking the size of the code and
> allowing for faster execution. When the code generator can guarantee
> that a particular pointer remains constant over a stretch of linear code
> (code with no jumps into it), and when that pointer is already loaded
> into a register pair (such as ES:DI), the code generator eliminates
> additional redundant pointer-load instructions in that block of code.
> A pointer is considered constant if it's obtained from a variable
> parameter (variable parameters are always passed as pointers) or from
> the variable reference of a WITH statement. Because of this, using WITH
> statements is often more efficient (but never less efficient) than
> writing the fully-qualified variable for each component reference."

FPC optimizes this as well (because the with-expression is only 
evaluated once). Though it's arguable in how far that is a micro 
optimization with today's CPUs.


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