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opt_dff: With -keepdc, never turn undef init vals into const drivers

This commit is contained in:
Jannis Harder 2022-06-29 15:35:28 +02:00
parent 869e6a1b6d
commit a47254bd10
1 changed files with 17 additions and 5 deletions
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22
passes/opt/opt_dff.cc
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@ -491,12 +491,17 @@ struct OptDffWorker
ff.has_srst = false; ff.has_srst = false;
ff.sig_d = ff.val_srst; ff.sig_d = ff.val_srst;
changed = true; 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("Handling never-active EN on %s (%s) from module %s (removing D path).\n",
log_id(cell), log_id(cell->type), log_id(module)); 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). // 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; ff.has_ce = ff.has_clk = ff.has_srst = false;
changed = true; 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)) { } else if (ff.sig_ce == (ff.pol_ce ? State::S1 : State::S0)) {
// Always-active enable. Just remove it. // Always-active enable. Just remove it.
@ -508,13 +513,20 @@ struct OptDffWorker
} }
} }
if (ff.has_clk) { if (ff.has_clk && ff.sig_clk.is_fully_const()) {
if (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). // 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("Handling const CLK on %s (%s) from module %s (removing D path).\n",
log_id(cell), log_id(cell->type), log_id(module)); log_id(cell), log_id(cell->type), log_id(module));
ff.has_ce = ff.has_clk = ff.has_srst = false; ff.has_ce = ff.has_clk = ff.has_srst = false;
changed = true; 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.has_srst = false;
ff.sig_d = ff.val_srst; ff.sig_d = ff.val_srst;
changed = true; 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). // 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("Handling D = Q on %s (%s) from module %s (removing D path).\n",
log_id(cell), log_id(cell->type), log_id(module)); 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. // 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) { if (!ff.has_arst && !ff.has_sr && (!ff.has_srst || !ff.has_ce || ff.ce_over_srst) && !opt.nosdff) {
// Try to merge sync resets. // Try to merge sync resets.
std::map<ctrls_t, std::vector<int>> groups; std::map<ctrls_t, std::vector<int>> groups;