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From: anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Sun, 08 Sep 2024 15:32:02 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
Lines: 53
Message-ID: <2024Sep8.173202@mips.complang.tuwien.ac.at>
References: <2024Aug30.161204@mips.complang.tuwien.ac.at> <vb2hir$1ju7q$1@dont-email.me> <8lcadjhnlcj5se1hrmo232viiccjk5alu4@4ax.com> <vb4amr$2rcbt$1@dont-email.me> <2024Sep5.133102@mips.complang.tuwien.ac.at> <vbchiv$cde4$1@dont-email.me> <2024Sep5.174939@mips.complang.tuwien.ac.at> <ljuc4fF86o3U2@mid.individual.net> <2024Sep6.092535@mips.complang.tuwien.ac.at> <20240906135718.00004f84@yahoo.com> <2024Sep6.152642@mips.complang.tuwien.ac.at> <65bc48543e1479699b5b2dff40c4f458@www.novabbs.org>
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mitchalsup@aol.com (MitchAlsup1) writes:
>And just for fun::
>
>On Fri, 6 Sep 2024 13:26:42 +0000, Anton Ertl wrote:
>> Here we have the three variants:
>>
>> #include <limits.h>
>>
>> extern long foo1(long);
>> extern long foo2(long);
>>
>> long bar(long a, long b)
>> {
>>   long c;
>>   if (__builtin_sub_overflow(b,1,&c))
>>     return foo1(a);
>>   else
>>     return foo2(a);
>> }
>>
>> long bar2(long a, long b)
>> {
>>   if (b < b-1)
>>     return foo1(a);
>>   else
>>     return foo2(a);
>> }
>>
>> long bar3(long a, long b)
>> {
>>   if (b == LONG_MIN)
>>     return foo1(a);
>>   else
>>     return foo2(a);
>> }
>
>My 66000:
>    add    r3,R1,#-1   add  r3,r1,#-1         bepm  r1,.L4
>    bge    R3,.L4      bge  r3,.L4
>    8-bytes            8-bytes                4-bytes
>
>I have a direct test for POSMAX in ISA that does not use a constant.

How does bge work in the first and second column?  My impression was
that you are using an 88k-style flags-in-GPR architecture.

Concerning the last column, the gcc developer who added the
transformation of bar2() into bar3() apparently had My66000 in mind.

- anton
-- 
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>