------- Comment #4 from jakub at gcc dot gnu dot org 2008-08-13 18:30 ------- Verified the regression was introduced by PR35163 fix. http://gcc.gnu.org/ml/gcc-patches/2008-04/msg00720.html should have been IMNSHO applied for shorter_type bigger or equal than arg1_unw's type, not just when they are equal. If shorter_type is bigger and the signs are different, then the bits above shorter_type bits might be all 1's in one case and all 0's in the second case.
Patch I'll be regtesting: 2008-08-13 Jakub Jelinek <[EMAIL PROTECTED]> PR middle-end/37103 * fold-const.c (fold_widened_comparison): Do not allow sign changes that change the result even if shorter type is wider than arg1_unw's type. * gcc.c-torture/execute/20080813-1.c: New test. --- gcc/fold-const.c.jj2008-08-13 19:46:11.000000000 +0200 +++ gcc/fold-const.c2008-08-13 20:18:21.000000000 +0200 @@ -6733,10 +6733,8 @@ fold_widened_comparison (enum tree_code if ((code == EQ_EXPR || code == NE_EXPR || TYPE_UNSIGNED (TREE_TYPE (arg0)) == TYPE_UNSIGNED (shorter_type)) && (TREE_TYPE (arg1_unw) == shorter_type - || (TYPE_PRECISION (shorter_type) - > TYPE_PRECISION (TREE_TYPE (arg1_unw))) || ((TYPE_PRECISION (shorter_type) - == TYPE_PRECISION (TREE_TYPE (arg1_unw))) + >= TYPE_PRECISION (TREE_TYPE (arg1_unw))) && (TYPE_UNSIGNED (shorter_type) == TYPE_UNSIGNED (TREE_TYPE (arg1_unw)))) || (TREE_CODE (arg1_unw) == INTEGER_CST --- gcc/testsuite/gcc.c-torture/execute/20080813-1.c.jj2008-08-13 20:22:56.000000000 +0200 +++ gcc/testsuite/gcc.c-torture/execute/20080813-1.c2008-08-13 20:22:10.000000000 +0200 @@ -0,0 +1,30 @@ +/* PR middle-end/37103 */ + +extern void abort (void); + +void +foo (unsigned short x) +{ + signed char y = -1; + if (x == y) + abort (); +} + +void +bar (unsigned short x) +{ + unsigned char y = -1; + if (x == y) + abort (); +} + +int +main (void) +{ + if (sizeof (int) == sizeof (short)) + return 0; + foo (-1); + if (sizeof (short) > 1) + bar (-1); + return 0; +} -- jakub at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- AssignedTo|unassigned at gcc dot gnu |jakub at gcc dot gnu dot org |dot org | Status|NEW |ASSIGNED Last reconfirmed|2008-08-13 09:16:17 |2008-08-13 18:30:25 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37103