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From: anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.compilers,comp.arch
Subject: Re: Assembling span-dependent instructions
Date: Thu, 28 Jul 2022 05:56:28 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
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Kaz Kylheku <480-992-1380@kylheku.com> writes:
>On 2022-07-27, Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>> However, one can also construct cases where making the code larger can
>> reduce the minimum size of the immediate operand, e.g.:
>>
>> foo:
>>      movl foo+133-bar(%rdi),%eax
>> bar:
>
>That's weird; what is accessed this way, relative to the code,
>and does it occur in compiler output?

I designed this example based on the examples in the paper, not as
something occuring in practice.

The examples in the paper involved several span-dependent instructions
and looked unusual to me, but I convinced myself that something like
that could occur in practice, with data close to code addressed using
some pointer into the code (like %rip-relative on AMD64, or the global
pointer on various position-independent ABIs for other architectures).

- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/