Re: Fix PR middle-end/14988

[Eric Botcazou <ebotcazou at act-europe dot fr>]

> If you test this on another platform (or two) without any problems, then
> this is OK for mainline.  Perhaps both a FRAME_GROWS_DOWNWARD and a
> FRAME_GROWS_UPWARD target?

I'm not sure I can test GCC head with FRAME_GROWS_UPWARD.  What mainstream 
platforms have F_G_U?

> From your analysis, the placement of CONCATs on the stack clearly needs to
> be fixed, and although your patch is better than what was there before, the
> expectation that the alignment and layout of the CONCAT will be the same as
> the sum of its individual components makes me nervous.

Isn't that the semantics of a CONCAT?  But I'm not 100% sure either.

> Isn't it possible that the CONCAT pair will require more alignment than
> just it's first component?  For example, I believe the s390 can store
> both floats of a SCmode value in a single register.  I'm unsure, but
> loading this register might require alignment beyond that of SFmode.

Would the SCmode value be given a CONCAT in the first place in that case?

> However, keeping the two components of a CONCAT sequential in memory is
> clearly an improvement, but I suspect that there may also be additional
> bugs lurking in this code.  Perhaps someone will convince me I've nothing
> to worry about.

Yes, I'm also under the impression that the patch (provided that the removal 
of promoted_mode is correct) can't hurt.

-- 
Eric Botcazou