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tuning bit-vector operations

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2015-12-21 13:09:03 +02:00
parent 1eebab355c
commit 8e26c97782
9 changed files with 271 additions and 94 deletions
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118
src/ast/rewriter/bv_rewriter.cpp
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@ -1968,7 +1968,63 @@ void bv_rewriter::mk_t1_add_t2_eq_c(expr * t1, expr * t2, expr * c, expr_ref & r
result = m().mk_eq(t1, m_util.mk_bv_sub(c, t2));
}
#include "ast_pp.h"
bool bv_rewriter::isolate_term(expr* lhs, expr* rhs, expr_ref& result) {
if (!m_util.is_numeral(lhs) || !is_add(rhs)) {
std::swap(lhs, rhs);
}
if (!m_util.is_numeral(lhs) || !is_add(rhs)) {
return false;
}
unsigned sz = to_app(rhs)->get_num_args();
expr_ref t1(m()), t2(m());
t1 = to_app(rhs)->get_arg(0);
if (sz > 2) {
t2 = m().mk_app(get_fid(), OP_BADD, sz-1, to_app(rhs)->get_args()+1);
}
else {
SASSERT(sz == 2);
t2 = to_app(rhs)->get_arg(1);
}
mk_t1_add_t2_eq_c(t1, t2, lhs, result);
return true;
}
bool bv_rewriter::is_add_mul_const(expr* e) const {
if (!m_util.is_bv_add(e)) {
return false;
}
unsigned num = to_app(e)->get_num_args();
for (unsigned i = 0; i < num; i++) {
expr * arg = to_app(e)->get_arg(i);
expr * c2, * x2;
if (m_util.is_numeral(arg))
continue;
if (m_util.is_bv_mul(arg, c2, x2) && m_util.is_numeral(c2))
continue;
return false;
}
return true;
}
bool bv_rewriter::is_concat_target(expr* lhs, expr* rhs) const {
return
m_util.is_concat(lhs) && (is_concat_split_target(rhs) || has_numeral(to_app(lhs))) ||
m_util.is_concat(rhs) && (is_concat_split_target(lhs) || has_numeral(to_app(rhs)));
}
bool bv_rewriter::has_numeral(app* a) const {
for (unsigned i = 0; i < a->get_num_args(); ++i) {
if (is_numeral(a->get_arg(i))) {
return true;
}
}
return false;
}
br_status bv_rewriter::mk_mul_eq(expr * lhs, expr * rhs, expr_ref & result) {
expr * c, * x;
numeral c_val, c_inv_val;
unsigned sz;
@ -2001,24 +2057,30 @@ br_status bv_rewriter::mk_mul_eq(expr * lhs, expr * rhs, expr_ref & result) {
// c * x = t_1 + ... + t_n
// and t_i's have non-unary coefficients (this condition is used to make sure we are actually reducing the number of multipliers).
if (m_util.is_bv_add(rhs)) {
if (is_add_mul_const(rhs)) {
// Potential problem: this simplification may increase the number of adders by reducing the amount of sharing.
unsigned num = to_app(rhs)->get_num_args();
unsigned i;
for (i = 0; i < num; i++) {
expr * arg = to_app(rhs)->get_arg(i);
expr * c2, * x2;
if (m_util.is_numeral(arg))
continue;
if (m_util.is_bv_mul(arg, c2, x2) && m_util.is_numeral(c2))
continue;
break;
}
if (i == num) {
result = m().mk_eq(x, m_util.mk_bv_mul(m_util.mk_numeral(c_inv_val, sz), rhs));
return BR_REWRITE2;
result = m().mk_eq(x, m_util.mk_bv_mul(m_util.mk_numeral(c_inv_val, sz), rhs));
return BR_REWRITE2;
}
}
if (m_util.is_numeral(lhs, c_val, sz) && is_add_mul_const(rhs)) {
unsigned sz = to_app(rhs)->get_num_args();
unsigned i = 0;
expr* c2, *x2;
numeral c2_val, c2_inv_val;
bool found = false;
for (; !found && i < sz; ++i) {
expr* arg = to_app(rhs)->get_arg(i);
if (m_util.is_bv_mul(arg, c2, x2) && m_util.is_numeral(c2, c2_val, sz) &&
m_util.mult_inverse(c2_val, sz, c2_inv_val)) {
found = true;
}
}
if (found) {
result = m().mk_eq(m_util.mk_numeral(c2_inv_val*c_val, sz),
m_util.mk_bv_mul(m_util.mk_numeral(c2_inv_val, sz), rhs));
return BR_REWRITE3;
}
}
return BR_FAILED;
}
@ -2065,9 +2127,10 @@ br_status bv_rewriter::mk_eq_core(expr * lhs, expr * rhs, expr_ref & result) {
return st;
}
expr_ref new_lhs(m());
expr_ref new_rhs(m());
if (m_util.is_bv_add(lhs) || m_util.is_bv_mul(lhs) || m_util.is_bv_add(rhs) || m_util.is_bv_mul(rhs)) {
expr_ref new_lhs(m());
expr_ref new_rhs(m());
st = cancel_monomials(lhs, rhs, false, new_lhs, new_rhs);
if (st != BR_FAILED) {
if (is_numeral(new_lhs) && is_numeral(new_rhs)) {
@ -2080,28 +2143,27 @@ br_status bv_rewriter::mk_eq_core(expr * lhs, expr * rhs, expr_ref & result) {
new_rhs = rhs;
}
lhs = new_lhs;
rhs = new_rhs;
// Try to rewrite t1 + t2 = c --> t1 = c - t2
// Reason: it is much cheaper to bit-blast.
expr * t1, * t2;
if (m_util.is_bv_add(new_lhs, t1, t2) && is_numeral(new_rhs)) {
mk_t1_add_t2_eq_c(t1, t2, new_rhs, result);
if (isolate_term(lhs, rhs, result)) {
return BR_REWRITE2;
}
if (m_util.is_bv_add(new_rhs, t1, t2) && is_numeral(new_lhs)) {
mk_t1_add_t2_eq_c(t1, t2, new_lhs, result);
return BR_REWRITE2;
if (is_concat_target(lhs, rhs)) {
return mk_eq_concat(lhs, rhs, result);
}
if (st != BR_FAILED) {
result = m().mk_eq(new_lhs, new_rhs);
result = m().mk_eq(lhs, rhs);
return BR_DONE;
}
}
if ((m_util.is_concat(lhs) && is_concat_split_target(rhs)) ||
(m_util.is_concat(rhs) && is_concat_split_target(lhs)))
if (is_concat_target(lhs, rhs)) {
return mk_eq_concat(lhs, rhs, result);
}
if (swapped) {
result = m().mk_eq(lhs, rhs);
return BR_DONE;