More aggressive $macc merging in alumacc

diff --git a/passes/techmap/alumacc.cc b/passes/techmap/alumacc.cc
index c52e0e4cac02e15d512c3315579e78bc2c2a3851..1115eead5d18614d157ec1871627d4cfbdf5974a 100644 (file)
--- a/passes/techmap/alumacc.cc
+++ b/passes/techmap/alumacc.cc
@@ -172,6 +172,42 @@ struct AlumaccWorker
                }
        }
 
+       static bool macc_may_overflow(Macc &macc, int width, bool is_signed)
+       {
+               std::vector<int> port_sizes;
+
+               for (auto &port : macc.ports) {
+                       if (port.is_signed != is_signed)
+                               return true;
+                       if (!port.is_signed && port.do_subtract)
+                               return true;
+                       if (SIZE(port.in_b))
+                               port_sizes.push_back(SIZE(port.in_a) + SIZE(port.in_b));
+                       else
+                               port_sizes.push_back(SIZE(port.in_a));
+               }
+
+               std::sort(port_sizes.begin(), port_sizes.end());
+
+               int acc_sum = 0, acc_shift = 0;
+               for (int sz : port_sizes) {
+                       while ((sz - acc_shift) > 20) {
+                               if (acc_sum & 1)
+                                       acc_sum++;
+                               acc_sum = acc_sum >> 1;
+                               acc_shift++;
+                       }
+                       acc_sum += (1 << (sz - acc_shift)) - 1;
+               }
+
+               while (acc_sum) {
+                       acc_sum = acc_sum >> 1;
+                       acc_shift++;
+               }
+
+               return acc_shift > width;
+       }
+
        void merge_macc()
        {
                while (1)
@@ -197,7 +233,7 @@ struct AlumaccWorker
                                        if (other_n->users > 1)
                                                continue;
 
-                                       if (SIZE(other_n->y) != SIZE(n->y))
+                                       if (SIZE(other_n->y) != SIZE(n->y) && macc_may_overflow(other_n->macc, SIZE(other_n->y), port.is_signed))
                                                continue;
 
                                        log("  merging $macc model for %s into %s.\n", log_id(other_n->cell), log_id(n->cell));