Richard,
this patch fixes PR53986.
The patch calculates the range of an LSHIFT_EXPR in case both operands are
constants ranges, and the operation is guaranteed not to overflow.
F.i., it evaluates [1, 2] << [1, 8] to [2, 512].
Bootstrapped and reg-tested (ada inclusive) on x86_64.
Ok for trunk?
Thanks,
- Tom
2012-08-25 Tom de Vries <t...@codesourcery.com>
PR tree-optimization/53986
* tree-vrp.c (extract_range_from_multiplicative_op_1): Allow
LSHIFT_EXPR.
(extract_range_from_binary_expr_1): Handle LSHIFT with constant range as
shift amount.
* gcc.dg/tree-ssa/vrp80.c: New test.
* gcc.dg/tree-ssa/vrp80-2.c: Same.
Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c (revision 190553)
+++ gcc/tree-vrp.c (working copy)
@@ -2068,7 +2068,8 @@ extract_range_from_multiplicative_op_1 (
|| code == CEIL_DIV_EXPR
|| code == EXACT_DIV_EXPR
|| code == ROUND_DIV_EXPR
- || code == RSHIFT_EXPR);
+ || code == RSHIFT_EXPR
+ || code == LSHIFT_EXPR);
gcc_assert ((vr0->type == VR_RANGE
|| (code == MULT_EXPR && vr0->type == VR_ANTI_RANGE))
&& vr0->type == vr1->type);
@@ -2767,6 +2768,27 @@ extract_range_from_binary_expr_1 (value_
flag_wrapv = saved_flag_wrapv;
return;
}
+ else if (code == LSHIFT_EXPR
+ && range_int_cst_p (&vr0))
+ {
+ int overflow_pos = TYPE_PRECISION (expr_type);
+ int bound_shift;
+ double_int bound;
+
+ if (!TYPE_UNSIGNED (expr_type))
+ overflow_pos -= 1;
+
+ bound_shift = overflow_pos - TREE_INT_CST_LOW (vr1.max);
+ bound = double_int_one.llshift (bound_shift,
+ TYPE_PRECISION (expr_type));
+ if (tree_to_double_int (vr0.max).ult (bound))
+ {
+ /* In the absense of overflow, (a << b) is equivalent
+ to (a * 2^b). */
+ extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1);
+ return;
+ }
+ }
}
set_value_range_to_varying (vr);
return;
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp80.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp80.c (revision 0)
@@ -0,0 +1,33 @@
+/* { dg-do link } */
+/* { dg-options "-O2 -fno-tree-switch-conversion" } */
+
+extern void link_error (void);
+
+/* Test <<. */
+
+void
+f3 (int s, int b)
+{
+ if (s >> 3 == -2)
+ /* s in range [-16, -9]. */
+ {
+ s += 17;
+ /* s in range [1, 8]. */
+ b = (b & 1) + 1;
+ /* b in range [1, 2]. */
+ b = b << s;
+ /* b in range [bmin << smin, bmax << smax],
+ == [1 << 1, 2 << 8]
+ == [2, 512]. */
+ if (b == 1 || b == 513)
+ link_error ();
+ }
+}
+
+int
+main ()
+{
+ return 0;
+}
+
+
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp80-2.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp80-2.c (revision 0)
@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-switch-conversion -fdump-tree-vrp1" } */
+
+extern void vrp_keep (void);
+
+/* Test <<. */
+
+void
+f3 (int s, int b)
+{
+ if (s >> 3 == -2)
+ /* s in range [-16, -9]. */
+ {
+ s += 17;
+ /* s in range [1, 8]. */
+ b = (b & 1) + 1;
+ /* b in range [1, 2]. */
+ b = b << s;
+ /* b in range [bmin << smin, bmax << smax],
+ == [1 << 1, 2 << 8]
+ == [2, 512]. */
+ if (b == 2)
+ vrp_keep ();
+ if (b == 512)
+ vrp_keep ();
+ }
+}
+
+int
+main ()
+{
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "vrp_keep \\(" 2 "vrp1"} } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */
+
+
