enum alg_code { alg_zero, alg_m, alg_shift,
alg_add_t_m2, alg_sub_t_m2,
alg_add_factor, alg_sub_factor,
- alg_add_t2_m, alg_sub_t2_m,
- alg_add, alg_subtract, alg_factor, alg_shiftop };
+ alg_add_t2_m, alg_sub_t2_m };
+
+/* This structure holds the "cost" of a multiply sequence. The
+ "cost" field holds the total rtx_cost of every operator in the
+ synthetic multiplication sequence, hence cost(a op b) is defined
+ as rtx_cost(op) + cost(a) + cost(b), where cost(leaf) is zero.
+ The "latency" field holds the minimum possible latency of the
+ synthetic multiply, on a hypothetical infinitely parallel CPU.
+ This is the critical path, or the maximum height, of the expression
+ tree which is the sum of rtx_costs on the most expensive path from
+ any leaf to the root. Hence latency(a op b) is defined as zero for
+ leaves and rtx_cost(op) + max(latency(a), latency(b)) otherwise. */
+
+struct mult_cost {
+ short cost; /* Total rtx_cost of the multiplication sequence. */
+ short latency; /* The latency of the multiplication sequence. */
+};
+
+/* This macro is used to compare a pointer to a mult_cost against an
+ single integer "rtx_cost" value. This is equivalent to the macro
+ CHEAPER_MULT_COST(X,Z) where Z = {Y,Y}. */
+#define MULT_COST_LESS(X,Y) ((X)->cost < (Y) \
+ || ((X)->cost == (Y) && (X)->latency < (Y)))
+
+/* This macro is used to compare two pointers to mult_costs against
+ each other. The macro returns true if X is cheaper than Y.
+ Currently, the cheaper of two mult_costs is the one with the
+ lower "cost". If "cost"s are tied, the lower latency is cheaper. */
+#define CHEAPER_MULT_COST(X,Y) ((X)->cost < (Y)->cost \
+ || ((X)->cost == (Y)->cost \
+ && (X)->latency < (Y)->latency))
/* This structure records a sequence of operations.
`ops' is the number of operations recorded.
struct algorithm
{
- short cost;
+ struct mult_cost cost;
short ops;
/* The size of the OP and LOG fields are not directly related to the
word size, but the worst-case algorithms will be if we have few
enum mult_variant {basic_variant, negate_variant, add_variant};
static void synth_mult (struct algorithm *, unsigned HOST_WIDE_INT,
- int, enum machine_mode mode);
+ const struct mult_cost *, enum machine_mode mode);
static bool choose_mult_variant (enum machine_mode, HOST_WIDE_INT,
struct algorithm *, enum mult_variant *, int);
static rtx expand_mult_const (enum machine_mode, rtx, HOST_WIDE_INT, rtx,
static void
synth_mult (struct algorithm *alg_out, unsigned HOST_WIDE_INT t,
- int cost_limit, enum machine_mode mode)
+ const struct mult_cost *cost_limit, enum machine_mode mode)
{
int m;
struct algorithm *alg_in, *best_alg;
- int cost;
+ struct mult_cost best_cost;
+ struct mult_cost new_limit;
+ int op_cost, op_latency;
unsigned HOST_WIDE_INT q;
int maxm = MIN (BITS_PER_WORD, GET_MODE_BITSIZE (mode));
/* Indicate that no algorithm is yet found. If no algorithm
is found, this value will be returned and indicate failure. */
- alg_out->cost = cost_limit;
+ alg_out->cost.cost = cost_limit->cost + 1;
- if (cost_limit <= 0)
+ if (cost_limit->cost < 0
+ || (cost_limit->cost == 0 && cost_limit->latency <= 0))
return;
/* Restrict the bits of "t" to the multiplication's mode. */
if (t == 1)
{
alg_out->ops = 1;
- alg_out->cost = 0;
+ alg_out->cost.cost = 0;
+ alg_out->cost.latency = 0;
alg_out->op[0] = alg_m;
return;
}
fail now. */
if (t == 0)
{
- if (zero_cost >= cost_limit)
+ if (MULT_COST_LESS (cost_limit, zero_cost))
return;
else
{
alg_out->ops = 1;
- alg_out->cost = zero_cost;
+ alg_out->cost.cost = zero_cost;
+ alg_out->cost.latency = zero_cost;
alg_out->op[0] = alg_zero;
return;
}
alg_in = alloca (sizeof (struct algorithm));
best_alg = alloca (sizeof (struct algorithm));
+ best_cost = *cost_limit;
/* If we have a group of zero bits at the low-order part of T, try
multiplying by the remaining bits and then doing a shift. */
/* The function expand_shift will choose between a shift and
a sequence of additions, so the observed cost is given as
MIN (m * add_cost[mode], shift_cost[mode][m]). */
- cost = m * add_cost[mode];
- if (shift_cost[mode][m] < cost)
- cost = shift_cost[mode][m];
- synth_mult (alg_in, q, cost_limit - cost, mode);
-
- cost += alg_in->cost;
- if (cost < cost_limit)
+ op_cost = m * add_cost[mode];
+ if (shift_cost[mode][m] < op_cost)
+ op_cost = shift_cost[mode][m];
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.latency = best_cost.latency - op_cost;
+ synth_mult (alg_in, q, &new_limit, mode);
+
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = m;
best_alg->op[best_alg->ops] = alg_shift;
- cost_limit = cost;
}
}
}
{
/* T ends with ...111. Multiply by (T + 1) and subtract 1. */
- cost = add_cost[mode];
- synth_mult (alg_in, t + 1, cost_limit - cost, mode);
+ op_cost = add_cost[mode];
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.latency = best_cost.latency - op_cost;
+ synth_mult (alg_in, t + 1, &new_limit, mode);
- cost += alg_in->cost;
- if (cost < cost_limit)
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = 0;
best_alg->op[best_alg->ops] = alg_sub_t_m2;
- cost_limit = cost;
}
}
else
{
/* T ends with ...01 or ...011. Multiply by (T - 1) and add 1. */
- cost = add_cost[mode];
- synth_mult (alg_in, t - 1, cost_limit - cost, mode);
+ op_cost = add_cost[mode];
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.latency = best_cost.latency - op_cost;
+ synth_mult (alg_in, t - 1, &new_limit, mode);
- cost += alg_in->cost;
- if (cost < cost_limit)
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = 0;
best_alg->op[best_alg->ops] = alg_add_t_m2;
- cost_limit = cost;
}
}
}
d = ((unsigned HOST_WIDE_INT) 1 << m) + 1;
if (t % d == 0 && t > d && m < maxm)
{
- cost = add_cost[mode] + shift_cost[mode][m];
- if (shiftadd_cost[mode][m] < cost)
- cost = shiftadd_cost[mode][m];
- synth_mult (alg_in, t / d, cost_limit - cost, mode);
+ /* If the target has a cheap shift-and-add instruction use
+ that in preference to a shift insn followed by an add insn.
+ Assume that the shift-and-add is "atomic" with a latency
+ equal to it's cost, otherwise assume that on superscalar
+ hardware the shift may be executed concurrently with the
+ earlier steps in the algorithm. */
+ op_cost = add_cost[mode] + shift_cost[mode][m];
+ if (shiftadd_cost[mode][m] < op_cost)
+ {
+ op_cost = shiftadd_cost[mode][m];
+ op_latency = op_cost;
+ }
+ else
+ op_latency = add_cost[mode];
+
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.latency = best_cost.latency - op_latency;
+ synth_mult (alg_in, t / d, &new_limit, mode);
- cost += alg_in->cost;
- if (cost < cost_limit)
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_latency;
+ if (alg_in->cost.latency < op_cost)
+ alg_in->cost.latency = op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = m;
best_alg->op[best_alg->ops] = alg_add_factor;
- cost_limit = cost;
}
/* Other factors will have been taken care of in the recursion. */
break;
d = ((unsigned HOST_WIDE_INT) 1 << m) - 1;
if (t % d == 0 && t > d && m < maxm)
{
- cost = add_cost[mode] + shift_cost[mode][m];
- if (shiftsub_cost[mode][m] < cost)
- cost = shiftsub_cost[mode][m];
- synth_mult (alg_in, t / d, cost_limit - cost, mode);
+ /* If the target has a cheap shift-and-subtract insn use
+ that in preference to a shift insn followed by a sub insn.
+ Assume that the shift-and-sub is "atomic" with a latency
+ equal to it's cost, otherwise assume that on superscalar
+ hardware the shift may be executed concurrently with the
+ earlier steps in the algorithm. */
+ op_cost = add_cost[mode] + shift_cost[mode][m];
+ if (shiftsub_cost[mode][m] < op_cost)
+ {
+ op_cost = shiftsub_cost[mode][m];
+ op_latency = op_cost;
+ }
+ else
+ op_latency = add_cost[mode];
+
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.cost = best_cost.cost - op_latency;
+ synth_mult (alg_in, t / d, &new_limit, mode);
- cost += alg_in->cost;
- if (cost < cost_limit)
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_latency;
+ if (alg_in->cost.latency < op_cost)
+ alg_in->cost.latency = op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = m;
best_alg->op[best_alg->ops] = alg_sub_factor;
- cost_limit = cost;
}
break;
}
m = exact_log2 (q);
if (m >= 0 && m < maxm)
{
- cost = shiftadd_cost[mode][m];
- synth_mult (alg_in, (t - 1) >> m, cost_limit - cost, mode);
-
- cost += alg_in->cost;
- if (cost < cost_limit)
+ op_cost = shiftadd_cost[mode][m];
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.latency = best_cost.latency - op_cost;
+ synth_mult (alg_in, (t - 1) >> m, &new_limit, mode);
+
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = m;
best_alg->op[best_alg->ops] = alg_add_t2_m;
- cost_limit = cost;
}
}
m = exact_log2 (q);
if (m >= 0 && m < maxm)
{
- cost = shiftsub_cost[mode][m];
- synth_mult (alg_in, (t + 1) >> m, cost_limit - cost, mode);
-
- cost += alg_in->cost;
- if (cost < cost_limit)
+ op_cost = shiftsub_cost[mode][m];
+ new_limit.cost = best_cost.cost - op_cost;
+ new_limit.latency = best_cost.latency - op_cost;
+ synth_mult (alg_in, (t + 1) >> m, &new_limit, mode);
+
+ alg_in->cost.cost += op_cost;
+ alg_in->cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
{
struct algorithm *x;
+ best_cost = alg_in->cost;
x = alg_in, alg_in = best_alg, best_alg = x;
best_alg->log[best_alg->ops] = m;
best_alg->op[best_alg->ops] = alg_sub_t2_m;
- cost_limit = cost;
}
}
}
- /* If cost_limit has not decreased since we stored it in alg_out->cost,
- we have not found any algorithm. */
- if (cost_limit == alg_out->cost)
- return;
-
/* If we are getting a too long sequence for `struct algorithm'
to record, make this search fail. */
if (best_alg->ops == MAX_BITS_PER_WORD)
return;
+ /* If best_cost has not decreased, we have not found any algorithm. */
+ if (!CHEAPER_MULT_COST (&best_cost, cost_limit))
+ return;
+
/* Copy the algorithm from temporary space to the space at alg_out.
We avoid using structure assignment because the majority of
best_alg is normally undefined, and this is a critical function. */
alg_out->ops = best_alg->ops + 1;
- alg_out->cost = cost_limit;
+ alg_out->cost = best_cost;
memcpy (alg_out->op, best_alg->op,
alg_out->ops * sizeof *alg_out->op);
memcpy (alg_out->log, best_alg->log,
int mult_cost)
{
struct algorithm alg2;
+ struct mult_cost limit;
+ int op_cost;
*variant = basic_variant;
- synth_mult (alg, val, mult_cost, mode);
+ limit.cost = mult_cost;
+ limit.latency = mult_cost;
+ synth_mult (alg, val, &limit, mode);
/* This works only if the inverted value actually fits in an
`unsigned int' */
if (HOST_BITS_PER_INT >= GET_MODE_BITSIZE (mode))
{
- synth_mult (&alg2, -val, MIN (alg->cost, mult_cost) - neg_cost[mode],
- mode);
- alg2.cost += neg_cost[mode];
- if (alg2.cost < alg->cost)
+ op_cost = neg_cost[mode];
+ if (MULT_COST_LESS (&alg->cost, mult_cost))
+ {
+ limit.cost = alg->cost.cost - op_cost;
+ limit.latency = alg->cost.latency - op_cost;
+ }
+ else
+ {
+ limit.cost = mult_cost - op_cost;
+ limit.latency = mult_cost - op_cost;
+ }
+
+ synth_mult (&alg2, -val, &limit, mode);
+ alg2.cost.cost += op_cost;
+ alg2.cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg2.cost, &alg->cost))
*alg = alg2, *variant = negate_variant;
}
/* This proves very useful for division-by-constant. */
- synth_mult (&alg2, val - 1, MIN (alg->cost, mult_cost) - add_cost[mode],
- mode);
- alg2.cost += add_cost[mode];
- if (alg2.cost < alg->cost)
+ op_cost = add_cost[mode];
+ if (MULT_COST_LESS (&alg->cost, mult_cost))
+ {
+ limit.cost = alg->cost.cost - op_cost;
+ limit.latency = alg->cost.latency - op_cost;
+ }
+ else
+ {
+ limit.cost = mult_cost - op_cost;
+ limit.latency = mult_cost - op_cost;
+ }
+
+ synth_mult (&alg2, val - 1, &limit, mode);
+ alg2.cost.cost += op_cost;
+ alg2.cost.latency += op_cost;
+ if (CHEAPER_MULT_COST (&alg2.cost, &alg->cost))
*alg = alg2, *variant = add_variant;
- return alg->cost < mult_cost;
+ return MULT_COST_LESS (&alg->cost, mult_cost);
}
/* A subroutine of expand_mult, used for constant multiplications.
{
/* See whether the specialized multiplication optabs are
cheaper than the shift/add version. */
- tem = expand_mult_highpart_optab (mode, op0, op1, target,
- unsignedp, alg.cost + extra_cost);
+ tem = expand_mult_highpart_optab (mode, op0, op1, target, unsignedp,
+ alg.cost.cost + extra_cost);
if (tem)
return tem;
projects / gcc.git / commitdiff