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Re: Enlarge MAX_ALLOCA?

From: David Kastrup
Subject: Re: Enlarge MAX_ALLOCA?
Date: Fri, 20 Jun 2014 11:38:57 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4.50 (gnu/linux)

Andreas Schwab <address@hidden> writes:

> Dmitry Antipov <address@hidden> writes:
>> IIUC this means that if alloca is limited to < 32K, stack may be expanded
>> with just one instruction because increment fits into an immediate operand.
>> Otherwise there should be a few more load/store/add instructions.
> If you use alloca you have a variable sized stack frame, so the offset
> will be variable as well.

Ah right, alloca is generally not something affecting the code
generation of unrelated code, so arrays allocated with alloca do not
change the offsets of scalar stack variables which are usually addressed
off a separate frame pointer unaffected by alloca.

So the addressing mode restrictions I brought up would be a red herring,
even when talking about something like 68k architectures.  So it seems
like indeed just the total stack size available (or not available) in
connection with the expected stack depth particularly including
functions using alloca that should govern the chosen sizes.

David Kastrup

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