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Create one $shiftx per bit in width

This commit is contained in:
Eddie Hung 2019-03-25 11:16:56 -07:00
parent 2507d01b03
commit b7a3d35c6b
1 changed files with 17 additions and 10 deletions
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25
passes/proc/proc_mux.cc
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@ -340,7 +340,7 @@ RTLIL::SigSpec signal_to_mux_tree(RTLIL::Module *mod, SnippetSwCache &swcache, d
// evaluate in reverse order to give the first entry the top priority // evaluate in reverse order to give the first entry the top priority
RTLIL::SigSpec initial_val = result; RTLIL::SigSpec initial_val = result;
RTLIL::Cell *last_mux_cell = NULL; RTLIL::Cell *last_mux_cell = NULL;
bool shiftx = true; bool shiftx = initial_val.is_fully_undef();
for (size_t i = 0; i < sw->cases.size(); i++) { for (size_t i = 0; i < sw->cases.size(); i++) {
int case_idx = sw->cases.size() - i - 1; int case_idx = sw->cases.size() - i - 1;
RTLIL::CaseRule *cs2 = sw->cases[case_idx]; RTLIL::CaseRule *cs2 = sw->cases[case_idx];
@ -355,20 +355,27 @@ RTLIL::SigSpec signal_to_mux_tree(RTLIL::Module *mod, SnippetSwCache &swcache, d
// Keep checking if case condition is the same as the current case index // Keep checking if case condition is the same as the current case index
if (cs2->compare.size() == 1 && cs2->compare.front().is_fully_const()) if (cs2->compare.size() == 1 && cs2->compare.front().is_fully_const())
shiftx = (cs2->compare.front().as_int() == case_idx); shiftx = (cs2->compare.front().as_int() == case_idx);
else
shiftx = false;
} }
} }
// Transform into a $shiftx if possible // Transform into a $shiftx where possible
if (shiftx && last_mux_cell->type == "$pmux") { if (shiftx && last_mux_cell->type == "$pmux") {
// Sanity check that A port of $pmux should be 'bx // Create bit-blasted $shiftx-es that shifts by the address line used in the case statement
log_assert(last_mux_cell->getPort("\\A").is_fully_undef()); auto pmux_b_port = last_mux_cell->getPort("\\B");
// Because we went in reverse order above, un-reverse its B port here auto pmux_y_port = last_mux_cell->getPort("\\Y");
auto b_port = last_mux_cell->getPort("\\B").chunks(); int width = last_mux_cell->getParam("\\WIDTH").as_int();
std::reverse(b_port.begin(), b_port.end()); for (int i = 0; i < width; ++i) {
RTLIL::SigSpec a_port;
// Because we went in reverse order above, un-reverse $pmux's B port here
for (int j = pmux_b_port.size()/width-1; j >= 0; --j)
a_port.append(pmux_b_port.extract(j*width+i, 1));
// Create a $shiftx that shifts by the address line used in the case statement // Create a $shiftx that shifts by the address line used in the case statement
mod->addShiftx(NEW_ID, b_port, sw->signal, last_mux_cell->getPort("\\Y")); mod->addShiftx(NEW_ID, a_port, sw->signal, pmux_y_port.extract(i, 1));
}
// Disconnect $pmux by replacing its output port with a floating wire // Disconnect $pmux by replacing its output port with a floating wire
last_mux_cell->setPort("\\Y", mod->addWire(NEW_ID, last_mux_cell->getParam("\\WIDTH").as_int())); last_mux_cell->setPort("\\Y", mod->addWire(NEW_ID, width));
} }
} }