This is the first patch to make the generated code for the testcase
in PR53355 better. It teaches VRP about LSHIFT_EXPRs (albeit only
of a very simple form).
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
Richard.
2012-05-15 Richard Guenther <rguent...@suse.de>
PR tree-optimization/53355
* tree-vrp.c (extract_range_from_binary_expr_1): Handle LSHIFT_EXPRs
by constants.
* gcc.dg/tree-ssa/vrp67.c: New testcase.
Index: gcc/tree-vrp.c
===================================================================
*** gcc/tree-vrp.c (revision 187503)
--- gcc/tree-vrp.c (working copy)
*************** extract_range_from_binary_expr_1 (value_
*** 2403,2408 ****
--- 2403,2409 ----
&& code != ROUND_DIV_EXPR
&& code != TRUNC_MOD_EXPR
&& code != RSHIFT_EXPR
+ && code != LSHIFT_EXPR
&& code != MIN_EXPR
&& code != MAX_EXPR
&& code != BIT_AND_EXPR
*************** extract_range_from_binary_expr_1 (value_
*** 2596,2601 ****
--- 2597,2636 ----
extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1);
return;
}
+ else if (code == LSHIFT_EXPR)
+ {
+ /* If we have a LSHIFT_EXPR with any shift values outside [0..prec-1],
+ then drop to VR_VARYING. Outside of this range we get undefined
+ behavior 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 (vr1.type != VR_RANGE
+ || !value_range_nonnegative_p (&vr1)
+ || TREE_CODE (vr1.max) != INTEGER_CST
+ || compare_tree_int (vr1.max, TYPE_PRECISION (expr_type) - 1) == 1)
+ {
+ set_value_range_to_varying (vr);
+ return;
+ }
+
+ /* We can map shifts by constants to MULT_EXPR handling. */
+ if (range_int_cst_singleton_p (&vr1))
+ {
+ value_range_t vr1p = { VR_RANGE, NULL_TREE, NULL_TREE, NULL };
+ vr1p.min
+ = double_int_to_tree (expr_type,
+ double_int_lshift (double_int_one,
+ TREE_INT_CST_LOW (vr1.min),
+ TYPE_PRECISION (expr_type),
+ false));
+ vr1p.max = vr1p.min;
+ extract_range_from_multiplicative_op_1 (vr, MULT_EXPR, &vr0, &vr1p);
+ return;
+ }
+
+ set_value_range_to_varying (vr);
+ return;
+ }
else if (code == TRUNC_DIV_EXPR
|| code == FLOOR_DIV_EXPR
|| code == CEIL_DIV_EXPR
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp67.c
===================================================================
*** gcc/testsuite/gcc.dg/tree-ssa/vrp67.c (revision 0)
--- gcc/testsuite/gcc.dg/tree-ssa/vrp67.c (revision 0)
***************
*** 0 ****
--- 1,38 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O2 -fdump-tree-vrp1" } */
+
+ unsigned foo (unsigned i)
+ {
+ if (i == 2)
+ {
+ i = i << 2;
+ if (i != 8)
+ link_error ();
+ }
+ return i;
+ }
+ unsigned bar (unsigned i)
+ {
+ if (i == 1 << (sizeof (unsigned) * 8 - 1))
+ {
+ i = i << 1;
+ if (i != 0)
+ link_error ();
+ }
+ return i;
+ }
+ unsigned baz (unsigned i)
+ {
+ i = i & 15;
+ if (i == 0)
+ return 0;
+ i = 1000 - i;
+ i >>= 1;
+ i <<= 1;
+ if (i == 0)
+ link_error ();
+ return i;
+ }
+
+ /* { dg-final { scan-tree-dump-times "Folding predicate" 3 "vrp1" } } */
+ /* { dg-final { cleanup-tree-dump "vrp1" } } */
