Re: Patch for incorrect execute/divconst-2.c

[Hans-Peter Nilsson <hp at bitrange dot com>]

On Tue, 14 Mar 2000, Jeffrey A Law wrote:
>   In message <Pine.BSF.4.10.10003110755460.17527-100000@dair.pair.com>you write
>   > Unfortunately this uncovers other GCC problems: the "quot * -2147483648"
>   > gets optimized into "quot << 31" on a host with 32-bit HOST_WIDE_INTs,
>   > regardless of sizeof long on the actual target,
> When precisely is that not a safe thing to do?

When "long int" (the type of quot) is 64 bits on the target.
It is then wrong since -2147483648L != (1 << 31).
The correct optimization would then be -(quot) << 31.

>   > Should I commit this, or break some more stuff? :-)
>   > Perhaps I should remove the ABS check, so it doesn't break on ix86-* self?
> Given that abs (-MAXINT) is undefined, that check should probably be removed.

Ok.  For a machine with 64-bit longs it is valid, though.

> The rest of the changes seem quite reasonable.

Thanks.  I take that as an "ok", and will install it in the next few days
with the ABS check in the patch replaced by this (somewhat sheepish)
comment:
/* For completeness, a check for "ABS (rem) < ABS (denom)" belongs here,
   but causes trouble on 32-bit machines and isn't worthwhile.  */

brgds, H-P