/* Initialize the variable expansions in loop preheader.
Callbacks for htab_traverse. PLACE_P is the loop-preheader
basic block where the initialization of the expansions
- should take place. */
+ should take place. The expansions are initialized with (-0)
+ when the operation is plus or minus to honor sign zero.
+ This way we can prevent cases where the sign of the final result is
+ effected by the sign of the expansion.
+ Here is an example to demonstrate this:
+
+ for (i = 0 ; i < n; i++)
+ sum += something;
+
+ ==>
+
+ sum += something
+ ....
+ i = i+1;
+ sum1 += something
+ ....
+ i = i+1
+ sum2 += something;
+ ....
+
+ When SUM is initialized with -zero and SOMETHING is also -zero; the
+ final result of sum should be -zero thus the expansions sum1 and sum2
+ should be initialized with -zero as well (otherwise we will get +zero
+ as the final result). */
static int
insert_var_expansion_initialization (void **slot, void *place_p)
basic_block place = (basic_block)place_p;
rtx seq, var, zero_init, insn;
unsigned i;
-
+ enum machine_mode mode = GET_MODE (ve->reg);
+ bool honor_signed_zero_p = HONOR_SIGNED_ZEROS (mode);
+
if (VEC_length (rtx, ve->var_expansions) == 0)
return 1;
if (ve->op == PLUS || ve->op == MINUS)
for (i = 0; VEC_iterate (rtx, ve->var_expansions, i, var); i++)
{
- zero_init = CONST0_RTX (GET_MODE (var));
+ if (honor_signed_zero_p)
+ zero_init = simplify_gen_unary (NEG, mode, CONST0_RTX (mode), mode);
+ else
+ zero_init = CONST0_RTX (mode);
+
emit_move_insn (var, zero_init);
}
else if (ve->op == MULT)