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Re: [patch] MIPS/gcc: Revert removal of DImode shifts for 32-bit targets

To: Richard Henderson <rth@redhat.com>
Subject: Re: [patch] MIPS/gcc: Revert removal of DImode shifts for 32-bit targets
From: Andreas Schwab <schwab@suse.de>
Date: Wed, 11 Aug 2004 02:24:37 +0200
Cc: Richard Sandiford <rsandifo@redhat.com>, "Maciej W. Rozycki" <macro@linux-mips.org>, Nigel Stephens <nigel@mips.com>, gcc-patches@gcc.gnu.org, linux-mips@linux-mips.org
In-reply-to: <20040810232020.GA21922@redhat.com> (Richard Henderson's message of "Tue, 10 Aug 2004 16:20:20 -0700")
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <Pine.LNX.4.58L.0407261325470.3873@blysk.ds.pg.gda.pl> <410E9E25.7080104@mips.com> <87acxcbxfl.fsf@redhat.com> <410F5964.3010109@mips.com> <876580bm2e.fsf@redhat.com> <410F60DF.9020400@mips.com> <Pine.LNX.4.58L.0408042123030.31930@blysk.ds.pg.gda.pl> <87r7qiwz54.fsf@redhat.com> <20040809220838.GE16493@redhat.com> <87zn5336h7.fsf@redhat.com> <20040810232020.GA21922@redhat.com>
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Richard Henderson <rth@redhat.com> writes:

> Patch seems ok then.  We'd have to add a new macro/target flag
> to handle non-truncating shifts -- we've got cases:
>
>   (1) Large shift shifts out all bits (ARM)
>   (2) Large shifts trap (VAX)
>   (3) Shift count truncated to 31, always, which means QI/HI
>       shifts are yield undefined results with large shifts.  (i386)
    (4) Shift count reduced modulo 64 (m68k)

Andreas.

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Andreas Schwab, SuSE Labs, schwab@suse.de
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