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Add fanout limit

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This commit is contained in:
Akash Levy 2024-10-25 19:55:57 -07:00
parent dd17e4c133
commit 751f463994
3 changed files with 18 additions and 4 deletions
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18
passes/cmds/splitfanout.cc
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@ -89,7 +89,7 @@ struct SplitfanoutWorker
toposort.sort(); toposort.sort();
} }
int split(Cell *cell) int split(Cell *cell, int limit)
{ {
// Get output signal/port // Get output signal/port
SigSpec outsig; SigSpec outsig;
@ -119,6 +119,12 @@ struct SplitfanoutWorker
if (GetSize(bit_users) <= 1) if (GetSize(bit_users) <= 1)
return 0; return 0;
// Skip if fanout is above limit
if (limit != -1 && GetSize(bit_users) > limit) {
log("Skipping %s cell %s/%s with high fanout %d.\n", log_id(cell->type), log_id(module), log_id(cell), GetSize(bit_users)-1);
return 0;
}
// Iterate over bit users and create a new cell for each one // Iterate over bit users and create a new cell for each one
log("Splitting %s cell %s/%s into %d copies based on fanout\n", log_id(cell->type), log_id(module), log_id(cell), GetSize(bit_users)-1); log("Splitting %s cell %s/%s into %d copies based on fanout\n", log_id(cell->type), log_id(module), log_id(cell), GetSize(bit_users)-1);
int foi = 0; int foi = 0;
@ -193,15 +199,23 @@ struct SplitfanoutPass : public Pass {
log("This command operates only on cells with 1 output and no 'bit split' on that\n"); log("This command operates only on cells with 1 output and no 'bit split' on that\n");
log("output.\n"); log("output.\n");
log("\n"); log("\n");
log(" -limit n\n");
log(" max fanout to split.\n");
log("\n");
} }
void execute(std::vector<std::string> args, RTLIL::Design *design) override void execute(std::vector<std::string> args, RTLIL::Design *design) override
{ {
int limit = -1;
log_header(design, "Executing SPLITFANOUT pass (splitting up cells with >1 fanout into copies).\n"); log_header(design, "Executing SPLITFANOUT pass (splitting up cells with >1 fanout into copies).\n");
size_t argidx; size_t argidx;
for (argidx = 1; argidx < args.size(); argidx++) for (argidx = 1; argidx < args.size(); argidx++)
{ {
// No options currently. When adding in the future make sure to update docstring with [options] // No options currently. When adding in the future make sure to update docstring with [options]
if (args[argidx] == "-limit" && argidx+1 < args.size()) {
limit = std::stoi(args[++argidx]);
continue;
}
break; break;
} }
extra_args(args, argidx, design); extra_args(args, argidx, design);
@ -213,7 +227,7 @@ struct SplitfanoutPass : public Pass {
SplitfanoutWorker worker(module); SplitfanoutWorker worker(module);
for (auto cell : worker.toposort.sorted) { for (auto cell : worker.toposort.sorted) {
int n = worker.split(module->cell(cell)); int n = worker.split(module->cell(cell), limit);
count_split_pre += (n != 0); count_split_pre += (n != 0);
count_split_post += n; count_split_post += n;
} }

2
passes/opt/muxpack.cc
View file

@ -370,7 +370,7 @@ struct MuxpackPass : public Pass {
extra_args(args, argidx, design); extra_args(args, argidx, design);
if (splitfanout) if (splitfanout)
Pass::call(design, "splitfanout t:$mux t:$pmux"); Pass::call(design, "splitfanout -limit 512 t:$mux t:$pmux");
int mux_count = 0; int mux_count = 0;
int pmux_count = 0; int pmux_count = 0;

2
passes/opt/opt_balance_tree.cc
View file

@ -330,7 +330,7 @@ struct OptBalanceTreePass : public Pass {
// Run splitfanout pass first // Run splitfanout pass first
if (splitfanout) if (splitfanout)
Pass::call(design, "splitfanout t:$and t:$or t:$xor t:$xnor t:$add t:$mul"); Pass::call(design, "splitfanout -limit 512 t:$and t:$or t:$xor t:$xnor t:$add t:$mul");
// Count of all cells that were packed // Count of all cells that were packed
dict<IdString, int> cell_count; dict<IdString, int> cell_count;