diff options
| -rw-r--r-- | passes/opt/opt_dff.cc | 22 |
1 files changed, 17 insertions, 5 deletions
diff --git a/passes/opt/opt_dff.cc b/passes/opt/opt_dff.cc index 0ad4acec2..6ff2d1b4b 100644 --- a/passes/opt/opt_dff.cc +++ b/passes/opt/opt_dff.cc @@ -491,12 +491,17 @@ struct OptDffWorker ff.has_srst = false; ff.sig_d = ff.val_srst; changed = true; - } else { + } else if (!opt.keepdc || ff.val_init.is_fully_def()) { log("Handling never-active EN on %s (%s) from module %s (removing D path).\n", log_id(cell), log_id(cell->type), log_id(module)); // The D input path is effectively useless, so remove it (this will be a D latch, SR latch, or a const driver). ff.has_ce = ff.has_clk = ff.has_srst = false; changed = true; + } else { + // We need to keep the undefined initival around as such + ff.sig_d = ff.sig_q; + ff.has_ce = ff.has_srst = false; + changed = true; } } else if (ff.sig_ce == (ff.pol_ce ? State::S1 : State::S0)) { // Always-active enable. Just remove it. @@ -508,13 +513,20 @@ struct OptDffWorker } } - if (ff.has_clk) { - if (ff.sig_clk.is_fully_const()) { + if (ff.has_clk && ff.sig_clk.is_fully_const()) { + if (!opt.keepdc || ff.val_init.is_fully_def()) { // Const clock — the D input path is effectively useless, so remove it (this will be a D latch, SR latch, or a const driver). log("Handling const CLK on %s (%s) from module %s (removing D path).\n", log_id(cell), log_id(cell->type), log_id(module)); ff.has_ce = ff.has_clk = ff.has_srst = false; changed = true; + } else { + // Const clock, but we need to keep the undefined initval around as such + if (ff.has_ce || ff.has_srst || ff.sig_d != ff.sig_q) { + ff.sig_d = ff.sig_q; + ff.has_ce = ff.has_srst = false; + changed = true; + } } } @@ -550,7 +562,7 @@ struct OptDffWorker ff.has_srst = false; ff.sig_d = ff.val_srst; changed = true; - } else { + } else if (!opt.keepdc || ff.val_init.is_fully_def()) { // The D input path is effectively useless, so remove it (this will be a const-input D latch, SR latch, or a const driver). log("Handling D = Q on %s (%s) from module %s (removing D path).\n", log_id(cell), log_id(cell->type), log_id(module)); @@ -567,7 +579,7 @@ struct OptDffWorker } // The cell has been simplified as much as possible already. Now try to spice it up with enables / sync resets. - if (ff.has_clk) { + if (ff.has_clk && ff.sig_d != ff.sig_q) { if (!ff.has_arst && !ff.has_sr && (!ff.has_srst || !ff.has_ce || ff.ce_over_srst) && !opt.nosdff) { // Try to merge sync resets. std::map<ctrls_t, std::vector<int>> groups; |