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From: anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Fri, 06 Sep 2024 07:16:43 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
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Bernd Linsel <bl1-thispartdoesnotbelonghere@gmx.com> writes:
>On 05.09.24 17:49, Anton Ertl wrote:
>> 
>> Nobody said that gcc did anything wrong here.  We were, however,
>> surprised that -fno-reorder-blocks did not suppress the reordering; we
>> reported this as bug, but were told that this option does something
>> different from what it says.  Anyway, we developed a workaround.  And
>> we also developed a workaround for the code duplication problem that
>> showed up in gcc-7.
>> 
>
>Have you tried interspersing `asm volatile("")` statements?
>
>It is very often an effective means to prevent gcc from reordering code 
>from before and after the asm statement.

We are using asm statements that result in no machine code for various
purposes (including the workaround for the code duplication of gcc-7
ff.)

We have not tried it for suppressing the basic block reordering, and I
would not expect such a statement to suppress that, because asm
volatile("") acts as a data-flow barrier, and basic-block reordering
has nothing to do with data flow.

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