PR tree-optimization/19903

	* tree-chrec.c (chrec_convert): Return chrec_dont_know for constants
	that don't fit in their type after conversion.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@97607 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 9f3a372..bbbade7 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2005-04-05  Eric Botcazou  <ebotcazou@libertysurf.fr>
+            Sebastian Pop <sebastian.pop@cri.ensmp.fr>
+
+       PR tree-optimization/19903
+       * tree-chrec.c (chrec_convert): Return chrec_dont_know for constants
+       that don't fit in their type after conversion.
+
 2005-04-05 Uros Bizjak <uros@kss-loka.si>
 
        PR target/20421

diff --git a/gcc/tree-chrec.c b/gcc/tree-chrec.c
index a360301..b6276e9 100644 (file)
--- a/gcc/tree-chrec.c
+++ b/gcc/tree-chrec.c
@@ -1002,7 +1002,23 @@ nb_vars_in_chrec (tree chrec)
 
 \f
 
-/* Convert the initial condition of chrec to type.  */
+/* Convert CHREC to TYPE.  The following is rule is always true:
+   TREE_TYPE (chrec) == TREE_TYPE (CHREC_LEFT (chrec)) == TREE_TYPE
+   (CHREC_RIGHT (chrec)).  An example of what could happen when adding
+   two chrecs and the type of the CHREC_RIGHT is different than
+   CHREC_LEFT is:
+   
+   {(uint) 0, +, (uchar) 10} +
+   {(uint) 0, +, (uchar) 250}
+   
+   that would produce a wrong result if CHREC_RIGHT is not (uint):
+   
+   {(uint) 0, +, (uchar) 4}
+
+   instead of
+
+   {(uint) 0, +, (uint) 260}
+*/
 
 tree 
 chrec_convert (tree type, 
@@ -1037,6 +1053,18 @@ chrec_convert (tree type,
        TREE_OVERFLOW (res) = 0;
        if (CONSTANT_CLASS_P (res))
          TREE_CONSTANT_OVERFLOW (res) = 0;
+
+       /* But reject constants that don't fit in their type after conversion.
+          This can happen if TYPE_MIN_VALUE or TYPE_MAX_VALUE are not the
+          natural values associated with TYPE_PRECISION and TYPE_UNSIGNED,
+          and can cause problems later when computing niters of loops.  Note
+          that we don't do the check before converting because we don't want
+          to reject conversions of negative chrecs to unsigned types.  */
+       if (TREE_CODE (res) == INTEGER_CST
+           && TREE_CODE (type) == INTEGER_TYPE
+           && !int_fits_type_p (res, type))
+         res = chrec_dont_know;
+
        return res;
       }
     }