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Gowin. BUGFIX. Alu optimization. 

Adding freeing of the addition/subtraction mode switch PIP.

We're limiting optimization to just one constant input—cases with two
constant inputs are rare, and this raises questions about how such ALUs
are generated in synthesis.

LUT knowledge calculations have been replaced with table
constants—faster and easier to verify.

Addresses https://github.com/YosysHQ/apicula/issues/514

Signed-off-by: YRabbit <rabbit@yrabbit.cyou>
This commit is contained in:
YRabbit 2026-06-16 16:52:30 +10:00
parent 2dfdba6efc
commit ae9a7dc865
1 changed files with 16 additions and 43 deletions
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59
himbaechel/uarch/gowin/pack_luts.cc
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@ -270,13 +270,6 @@ std::unique_ptr<CellInfo> GowinPacker::alu_add_dummy_block(Context *ctx, CellInf
// 0110 -> 0011
void GowinPacker::optimize_alu_lut(CellInfo *ci, int mode)
{
auto uni_shift = [&](unsigned int val, int amount) {
if (amount < 0) {
return val >> -amount;
}
return val << amount;
};
IdString vcc_net_name = ctx->id("$PACKER_VCC");
IdString gnd_net_name = ctx->id("$PACKER_GND");
bool optimized = false;
@ -288,57 +281,37 @@ void GowinPacker::optimize_alu_lut(CellInfo *ci, int mode)
// representation.
// If ADDSUB dynamically switches between + and -,
// optimization is not possible.
int possible_carry = 0b1100U;
IdString inp_net_name = ci->getPort(id_I3)->name;
if (inp_net_name != vcc_net_name && inp_net_name != gnd_net_name) {
break;
}
if (inp_net_name == gnd_net_name) {
possible_carry = 0b0011U;
}
unsigned int alu_lut = 0b0110000010011010U;
for (int i = 0; i < 3; ++i) {
if (i == 2) {
break;
}
bool addition = inp_net_name == vcc_net_name;
unsigned int alu_lut;
for (int i = 0; i < 2; ++i) {
IdString inp_name = ctx->idf("I%d", i);
inp_net_name = ci->getPort(inp_name)->name;
if (inp_net_name == vcc_net_name || inp_net_name == gnd_net_name) {
ci->disconnectPort(inp_name);
// disconnect +/- selector
ci->disconnectPort(id_I3);
optimized = true;
// fix the carry
if (i == 0) {
if (inp_net_name == vcc_net_name) {
alu_lut |= 0xfU;
alu_lut = addition ? 0x303fU : 0xc0cfU;
} else {
alu_lut &= ~0xfU;
alu_lut |= possible_carry;
alu_lut = addition ? 0xc0c0U : 0x3030U;
}
} else {
if (inp_net_name == vcc_net_name) {
alu_lut = addition ? 0x505aU : 0xa0aaU;
} else {
alu_lut = addition ? 0xa0aaU : 0x505aU;
}
}
// We rearrange bits to account for constant networks
int bit_n = 4;
int copy_dist = 1 << i;
if (inp_net_name == vcc_net_name) {
bit_n += copy_dist;
copy_dist = -copy_dist;
}
for (int j = 0; j < 4; ++j) {
alu_lut &= ~(1 << (bit_n + copy_dist));
alu_lut |= uni_shift(alu_lut & (1 << bit_n), copy_dist);
switch (i) {
case 0: // skip the service bits
bit_n += j == 1 ? 5 : 1;
break;
case 1: // skip the service bits
bit_n += j == 1 ? 6 : 0;
break;
default:
break;
}
++bit_n;
}
break;
}
}
if (optimized) {