From: rth <rth@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Sun, 1 Apr 2007 18:17:38 +0000 (+0000)
Subject:         PR tree-optimization/31169
X-Git-Url: http://git.sourceforge.jp/view?p=pf3gnuchains%2Fgcc-fork.git;a=commitdiff_plain;h=6291249b40959d2fba26f20841b0bcc4bf63d80d

    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 7d8f39bb7d9..81606be4cd3 100644
--- 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 3b7358dc032..dbb97de887a 100644
--- 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;