Re: C compiler for PDP-11 sought, optimizing for size in general

leob@mailcom.com wrote:
> I am looking for an optimizing compiler that can take ANSI C (I know
> about unprotoize, so a K&R C compiler will do) and produces PDP-11
> assembly code that is optimized for size rather than for speed.


[snip]


> But even if the GCC port had been finished, the way GCC optimizes for
> size is quite lightweight: the impact of forcing a variable or an
> address into a register is not analyzed wrt the code size, to start
> with: try compiling
>
> void foo() {
> extern int a;
> if(++a) ++a;
> }
>
> with various options for i386 to see what I'm talking about;
> no way you can make it produce
>
> foo: addl $1,a
> je .L1
> addl $1,a
> ..L1: ret


Wanna bet?


Using gcc -O -fomit-framepointer I got it to produce:


foo:
                incl a
                je .L3
                incl a
..L3:
                ret


which seems fairly optimal to me.
(Granted, just about any other combination of flags seems to produce
similar unnecessary as you show below.


>
> the best I got is (-O4 -Os)
> foo:
> movl a, %edx
> leal 1(%edx), %eax
> testl %eax, %eax
> movl %eax, a
> je .L1
> leal 2(%edx), %eax
> movl %eax, a
> ..L1:
> ret
>


--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se

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