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Optimize shift ops with constant rhs in opt_const

This commit is contained in:
Clifford Wolf 2014-08-24 17:08:07 +02:00
parent 641501203c
commit 7bbbe3580d
1 changed files with 35 additions and 0 deletions
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35
passes/opt/opt_const.cc
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@ -558,6 +558,41 @@ static void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bo
}
}
if (cell->type.in("$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx") && assign_map(cell->getPort("\\B")).is_fully_const())
{
bool sign_ext = cell->type == "$sshr" && cell->getParam("\\A_SIGNED").as_bool();
int shift_bits = assign_map(cell->getPort("\\B")).as_int(cell->type.in("$shift", "$shiftx") && cell->getParam("\\B_SIGNED").as_bool());
if (cell->type.in("$shl", "$sshl"))
shift_bits *= -1;
RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
RTLIL::SigSpec sig_y(cell->type == "$shiftx" ? RTLIL::State::Sx : RTLIL::State::S0, cell->getParam("\\Y_WIDTH").as_int());
if (SIZE(sig_a) < SIZE(sig_y))
sig_a.extend(SIZE(sig_y), cell->getParam("\\A_SIGNED").as_bool());
for (int i = 0; i < SIZE(sig_y); i++) {
int idx = i + shift_bits;
if (0 <= idx && idx < SIZE(sig_a))
sig_y[i] = sig_a[idx];
else if (SIZE(sig_a) <= idx && sign_ext)
sig_y[i] = sig_a[SIZE(sig_a)-1];
}
cover_list("opt.opt_const.constshift", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", cell->type.str());
log("Replacing %s cell `%s' (B=%s, SHR=%d) in module `%s' with fixed wiring: %s\n",
log_id(cell->type), log_id(cell), log_signal(assign_map(cell->getPort("\\B"))), shift_bits, log_id(module), log_signal(sig_y));
module->connect(cell->getPort("\\Y"), sig_y);
module->remove(cell);
OPT_DID_SOMETHING = true;
did_something = true;
goto next_cell;
}
if (!keepdc)
{
bool identity_bu0 = false;