Hi,
this is the failure of gcc.dg/tree-ssa/ivopts-lt-2.c on SPARC 64-bit, but I
think that the problem is actually generic: get_shiftadd_cost only calls
shiftadd_cost to get the cost of a "shift-add", which is actually a multiply
by a power-of-2 operation. Since SPARC doesn't have a lea-like instruction,
shiftadd_cost returns a very high cost, about 3 times the cost of an add+shift
sequence which is what the RTL expander will generate for this operation.
So I think that get_shiftadd_cost should mimic the algorithms in expmed.c and
use the minimum of shiftadd_cost and (add_cost + shift_cost) for the cost of
the shift-add operation.
Tested on x86-64, SPARC and SPARC64, OK for the mainline?
2015-02-05 Eric Botcazou <ebotca...@adacore.com>
PR target/62631
* tree-ssa-loop-ivopts.c (get_shiftadd_cost): Use the mininum of costs
of shift-add and (add + shift) operations. Rename local variable.
--
Eric Botcazou--- tree-ssa-loop-ivopts.c (revision 220343)
+++ tree-ssa-loop-ivopts.c (working copy)
@@ -3597,22 +3597,26 @@ get_shiftadd_cost (tree expr, machine_mo
tree multop = TREE_OPERAND (mult, 0);
int m = exact_log2 (int_cst_value (cst));
int maxm = MIN (BITS_PER_WORD, GET_MODE_BITSIZE (mode));
- int sa_cost;
- bool equal_p = false;
+ int as_cost, sa_cost;
+ bool mult_in_op1;
if (!(m >= 0 && m < maxm))
return false;
- if (operand_equal_p (op1, mult, 0))
- equal_p = true;
+ mult_in_op1 = operand_equal_p (op1, mult, 0);
+ as_cost = add_cost (speed, mode) + shift_cost (speed, mode, m);
+
+ /* If the target has a cheap shift-and-add or shift-and-sub instruction,
+ use that in preference to a shift insn followed by an add insn. */
sa_cost = (TREE_CODE (expr) != MINUS_EXPR
? shiftadd_cost (speed, mode, m)
- : (equal_p
+ : (mult_in_op1
? shiftsub1_cost (speed, mode, m)
: shiftsub0_cost (speed, mode, m)));
- res = new_cost (sa_cost, 0);
- res = add_costs (res, equal_p ? cost0 : cost1);
+
+ res = new_cost (MIN (as_cost, sa_cost), 0);
+ res = add_costs (res, mult_in_op1 ? cost0 : cost1);
STRIP_NOPS (multop);
if (!is_gimple_val (multop))
