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Re: [avr-gcc-list] Weird optimization issue with avr-gcc 4.5.3, re "nake

From: Georg-Johann Lay
Subject: Re: [avr-gcc-list] Weird optimization issue with avr-gcc 4.5.3, re "naked."
Date: Sat, 28 Jan 2012 00:32:00 +0100
User-agent: Mozilla Thunderbird 1.0.7 (Windows/20050923)

Jan Waclawek schrieb:

Moreover, in 4.7 it also stores the variable to stack frame even
without naked, so that could be called a missed

Thanks for pointing this out. I was lost in all that optimization conversation and thought it was an optimization issue from the first post.

There is nothing written like "program crashes because non-existent frame used".

So the very problem is that there is a frame needed and there is none because of "naked".

Well, that's a bug in the user code, not in the application:
You must not assume that the C code need no frame, even if it is a reasonable assumption like here.

However, the frame is really strange and my first suspect is the evildoer: -fcaller-saves.

That option causes evil in some places, or let me put things the other way round: In some cases -fno-caller-saves can avoid harm like spill fails in presence of high register pressure, see PR50925.


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