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Re: suspect code in fold-const.c
- From: Jeff Law <law at redhat dot com>
- To: Kenneth Zadeck <zadeck at naturalbridge dot com>, GCC Development <gcc at gcc dot gnu dot org>, Richard Sandiford <rdsandiford at googlemail dot com>, Richard Biener <rguenther at suse dot de>
- Date: Thu, 14 Nov 2013 22:07:27 -0700
- Subject: Re: suspect code in fold-const.c
- Authentication-results: sourceware.org; auth=none
- References: <5284F74F dot 4050600 at naturalbridge dot com>
On 11/14/13 09:16, Kenneth Zadeck wrote:
in doing the wide int conversion, i have found the following code on the
trunk which seems somewhat suspect:
this code from fold-const.c starts on line 13811.
else if (TREE_INT_CST_HIGH (arg1) == signed_max_hi
&& TREE_INT_CST_LOW (arg1) == signed_max_lo
&& TYPE_UNSIGNED (arg1_type)
/* We will flip the signedness of the comparison operator
associated with the mode of arg1, so the sign bit is
specified by this mode. Check that arg1 is the signed
max associated with this sign bit. */
&& width == GET_MODE_BITSIZE (TYPE_MODE (arg1_type))
/* signed_type does not work on pointer types. */
&& INTEGRAL_TYPE_P (arg1_type))
it seems that the check on bitsize should really be a check on the
precision of the variable. If this seems right, i will correct this on
the trunk and make the appropriate changes to the wide-int branch.
I'd strongly suggest talking with Eric. It looks like the mode test is
on purpose. From the change which introduced that code:
commit 8aa01816af90c5c9b6e3718ee263678ce5f3d93e
Author: ebotcazou <ebotcazou@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Fri Dec 1 22:46:45 2006 +0000
* fold-const.c (fold_binary) <LT_EXPR>: Use the precision of the
type instead of the size of its mode to compute the highest and
lowest possible values. Still check the size of the mode before
flipping the signedness of the comparison.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@119422
138bc75d-0d04-0410-96
And it's associated thread on gcc-patches:
http://gcc.gnu.org/ml/gcc-patches/2006-11/msg00242.html