PR tree-optimization/31169

        * tree-vrp.c (extract_range_from_binary_expr) <RSHIFT_EXPR>: Drop
        to varying if the range is outside [0,  prec-1].

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@123405 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7d8f39b..81606be 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2007-04-01  Richard Henderson  <rth@redhat.com>
+
+       PR tree-optimization/31169
+       * tree-vrp.c (extract_range_from_binary_expr) <RSHIFT_EXPR>: Drop
+       to varying if the range is outside [0,  prec-1].
+
 2007-04-01  Richard Sandiford  <richard@codesourcery.com>
 
        PR target/31388

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 3b7358d..dbb97de 100644 (file)
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -1813,15 +1813,23 @@ extract_range_from_binary_expr (value_range_t *vr, tree expr)
          return;
        }
 
-      /* If we have a RSHIFT_EXPR with a possibly negative shift
-        count or an anti-range shift count drop to VR_VARYING.
-        We currently cannot handle the overflow cases correctly.  */
-      if (code == RSHIFT_EXPR
-         && (vr1.type == VR_ANTI_RANGE
-             || !vrp_expr_computes_nonnegative (op1, &sop)))
+      /* If we have a RSHIFT_EXPR with any shift values outside [0..prec-1],
+        then drop to VR_VARYING.  Outside of this range we get undefined
+        behaviour from the shift operation.  We cannot even trust
+        SHIFT_COUNT_TRUNCATED at this stage, because that applies to rtl
+        shifts, and the operation at the tree level may be widened.  */
+      if (code == RSHIFT_EXPR)
        {
-         set_value_range_to_varying (vr);
-         return;
+         if (vr1.type == VR_ANTI_RANGE
+             || !vrp_expr_computes_nonnegative (op1, &sop)
+             || (operand_less_p
+                 (build_int_cst (TREE_TYPE (vr1.max),
+                                 TYPE_PRECISION (TREE_TYPE (expr)) - 1),
+                  vr1.max) != 0))
+           {
+             set_value_range_to_varying (vr);
+             return;
+           }
        }
 
       /* Multiplications and divisions are a bit tricky to handle,
@@ -1838,9 +1846,8 @@ extract_range_from_binary_expr (value_range_t *vr, tree expr)
         the new range.  */
 
       /* Divisions by zero result in a VARYING value.  */
-      if ((code != MULT_EXPR
-          && code != RSHIFT_EXPR)
-         && (vr0.type == VR_ANTI_RANGE || range_includes_zero_p (&vr1)))
+      else if (code != MULT_EXPR
+              && (vr0.type == VR_ANTI_RANGE || range_includes_zero_p (&vr1)))
        {
          set_value_range_to_varying (vr);
          return;