{
const struct loop_info *loop_info = LOOP_INFO (loop);
HOST_WIDE_INT abs_inc;
+ HOST_WIDE_INT abs_loop_inc;
int neg_inc;
rtx diff;
rtx sequence;
except in cases where the loop never terminates. So we don't
need to use this more costly calculation.
- If the loop has been unrolled, then the loop body has been
- preconditioned to iterate a multiple of unroll_number times. If
- abs_inc is != 1, the full calculation is
+ If the loop has been unrolled, the full calculation is
- t1 = abs_inc * unroll_number;
- n = abs (final - initial) / t1;
- n += (abs (final - initial) % t1) > t1 - abs_inc;
+ t1 = abs_inc * unroll_number; increment per loop
+ n = abs (final - initial) / t1; full loops
+ n += (abs (final - initial) % t1) != 0; partial loop
+
+ However, in certain cases the unrolled loop will be preconditioned
+ by emitting copies of the loop body with conditional branches,
+ so that the unrolled loop is always a full loop and thus needs
+ no exit tests. In this case we don't want to add the partial
+ loop count. As above, when t1 is a power of two we don't need to
+ worry about overflow.
The division and modulo operations can be avoided by requiring
that the increment is a power of 2 (precondition_loop_p enforces
}
}
- if (abs_inc * loop_info->unroll_number != 1)
+ abs_loop_inc = abs_inc * loop_info->unroll_number;
+ if (abs_loop_inc != 1)
{
int shift_count;
- shift_count = exact_log2 (abs_inc * loop_info->unroll_number);
+ shift_count = exact_log2 (abs_loop_inc);
if (shift_count < 0)
abort ();
- if (abs_inc != 1)
+ if (!loop_info->preconditioned)
diff = expand_simple_binop (GET_MODE (diff), PLUS,
- diff, GEN_INT (abs_inc - 1),
+ diff, GEN_INT (abs_loop_inc - 1),
diff, 1, OPTAB_LIB_WIDEN);
- /* (abs (final - initial) + abs_inc - 1) / (abs_inc * unroll_number) */
+ /* (abs (final - initial) + abs_inc * unroll_number - 1)
+ / (abs_inc * unroll_number) */
diff = expand_simple_binop (GET_MODE (diff), LSHIFTRT,
diff, GEN_INT (shift_count),
diff, 1, OPTAB_LIB_WIDEN);
/* Keep track of the unroll factor for the loop. */
loop_info->unroll_number = unroll_number;
+ /* And whether the loop has been preconditioned. */
+ loop_info->preconditioned = loop_preconditioned;
+
/* For each biv and giv, determine whether it can be safely split into
a different variable for each unrolled copy of the loop body.
We precalculate and save this info here, since computing it is