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opt_expr: refactor simplification of signed X>=0 and X<0. NFCI.

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This commit is contained in:
whitequark 2019-01-02 03:01:25 +00:00
parent 8e53d2e0bf
commit 9e9846a6ea
2 changed files with 40 additions and 32 deletions
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50
passes/opt/opt_expr.cc
View file

@ -1373,38 +1373,59 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
if (const_sig.is_fully_def() && const_sig.is_fully_const())
{
const char *condition, *replacement;
std::string condition, replacement;
SigSpec result_sig(State::S0, GetSize(cell->getPort("\\Y")));
result_sig[0] = State::Sx;
bool replace = false;
if (!is_signed)
{
{ /* unsigned */
if (const_sig.is_fully_zero() && cmp_type == "$lt") {
condition = "unsigned X<0";
replacement = "constant 0";
result_sig[0] = State::S0;
replace = true;
}
if (const_sig.is_fully_zero() && cmp_type == "$ge") {
condition = "unsigned X>=0";
replacement = "constant 1";
result_sig[0] = State::S1;
replace = true;
}
if (const_width == var_width && const_sig.is_fully_ones() && cmp_type == "$gt") {
condition = "unsigned X>~0";
replacement = "constant 0";
result_sig[0] = State::S0;
replace = true;
}
if (const_width == var_width && const_sig.is_fully_ones() && cmp_type == "$le") {
condition = "unsigned X<=~0";
replacement = "constant 1";
result_sig[0] = State::S1;
replace = true;
}
}
else
{ /* signed */
if (const_sig.is_fully_zero() && cmp_type == "$lt")
{
condition = "signed X<0";
replacement = stringf("X[%d]", var_width - 1);
result_sig[0] = var_sig[var_width - 1];
replace = true;
}
if (const_sig.is_fully_zero() && cmp_type == "$ge")
{
condition = "signed X>=0";
replacement = stringf("X[%d]", var_width - 1);
module->addNot(NEW_ID, var_sig[var_width - 1], result_sig);
replace = true;
}
}
if (result_sig.is_fully_def())
if (replace)
{
log("Replacing %s cell `%s' (implementing %s) with %s.\n",
log_id(cell->type), log_id(cell), condition, replacement);
log_id(cell->type), log_id(cell), condition.c_str(), replacement.c_str());
module->connect(cell->getPort("\\Y"), result_sig);
module->remove(cell);
did_something = true;
@ -1453,25 +1474,6 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
} else
log_abort();
// replace a(signed) < 0 with the high bit of a
if (sigConst.is_fully_const() && sigConst.is_fully_zero() && var_signed == true)
{
RTLIL::SigSpec a_prime(RTLIL::State::S0, cell->parameters["\\Y_WIDTH"].as_int());
a_prime[0] = sigVar[width - 1];
if (is_lt) {
log("Replacing %s cell `%s' (implementing X<0) with X[%d]: %s\n",
log_id(cell->type), log_id(cell), width-1, log_signal(a_prime));
module->connect(cell->getPort("\\Y"), a_prime);
module->remove(cell);
} else {
log("Replacing %s cell `%s' (implementing X>=0) with ~X[%d]: %s\n",
log_id(cell->type), log_id(cell), width-1, log_signal(a_prime));
module->addNot(NEW_ID, a_prime, cell->getPort("\\Y"));
module->remove(cell);
}
did_something = true;
goto next_cell;
} else
if (sigConst.is_fully_const() && sigConst.is_fully_def() && var_signed == false)
{
int const_bit_set = get_onehot_bit_index(sigConst);

22
tests/opt/opt_expr_cmp.v
View file

@ -1,11 +1,17 @@
module top(...);
input [3:0] a;
output o1 = 4'b0000 > a;
output o2 = 4'b0000 <= a;
output o3 = 4'b1111 < a;
output o4 = 4'b1111 >= a;
output o5 = a < 4'b0000;
output o6 = a >= 4'b0000;
output o7 = a > 4'b1111;
output o8 = a <= 4'b1111;
output o1_1 = 4'b0000 > a;
output o1_2 = 4'b0000 <= a;
output o1_3 = 4'b1111 < a;
output o1_4 = 4'b1111 >= a;
output o1_5 = a < 4'b0000;
output o1_6 = a >= 4'b0000;
output o1_7 = a > 4'b1111;
output o1_8 = a <= 4'b1111;
output o2_1 = 4'sb0000 > $signed(a);
output o2_2 = 4'sb0000 <= $signed(a);
output o2_3 = $signed(a) < 4'sb0000;
output o2_4 = $signed(a) >= 4'sb0000;
endmodule