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Added opt_expr support for div/mod by power-of-two

This commit is contained in:
Clifford Wolf 2016-05-29 12:17:36 +02:00
parent 766032c5f8
commit 11f7b8a2a1
2 changed files with 96 additions and 0 deletions
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69
passes/opt/opt_expr.cc
View File

@ -1098,6 +1098,75 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
}
}
if (!keepdc && cell->type.in("$div", "$mod"))
{
bool b_signed = cell->parameters["\\B_SIGNED"].as_bool();
SigSpec sig_b = assign_map(cell->getPort("\\B"));
SigSpec sig_y = assign_map(cell->getPort("\\Y"));
if (sig_b.is_fully_def() && sig_b.size() <= 32)
{
int b_val = sig_b.as_int();
if (b_val == 0)
{
cover("opt.opt_expr.divmod_zero");
log("Replacing divide-by-zero cell `%s' in module `%s' with undef-driver.\n",
cell->name.c_str(), module->name.c_str());
module->connect(RTLIL::SigSig(sig_y, RTLIL::SigSpec(State::Sx, sig_y.size())));
module->remove(cell);
did_something = true;
goto next_cell;
}
for (int i = 1; i < (b_signed ? sig_b.size()-1 : sig_b.size()); i++)
if (b_val == (1 << i))
{
if (cell->type == "$div")
{
cover("opt.opt_expr.div_shift");
log("Replacing divide-by-%d cell `%s' in module `%s' with shift-by-%d.\n",
b_val, cell->name.c_str(), module->name.c_str(), i);
std::vector<RTLIL::SigBit> new_b = RTLIL::SigSpec(i, 6);
while (GetSize(new_b) > 1 && new_b.back() == RTLIL::State::S0)
new_b.pop_back();
cell->type = "$shr";
cell->parameters["\\B_WIDTH"] = GetSize(new_b);
cell->parameters["\\B_SIGNED"] = false;
cell->setPort("\\B", new_b);
cell->check();
}
else
{
cover("opt.opt_expr.mod_mask");
log("Replacing modulo-by-%d cell `%s' in module `%s' with bitmask.\n",
b_val, cell->name.c_str(), module->name.c_str());
std::vector<RTLIL::SigBit> new_b = RTLIL::SigSpec(State::S1, i);
if (b_signed)
new_b.push_back(State::S0);
cell->type = "$and";
cell->parameters["\\B_WIDTH"] = GetSize(new_b);
cell->setPort("\\B", new_b);
cell->check();
}
did_something = true;
goto next_cell;
}
}
}
next_cell:;
#undef ACTION_DO
#undef ACTION_DO_Y

27
tests/simple/constmuldivmod.v Normal file
View File

@ -0,0 +1,27 @@
module constmuldivmod(input [7:0] A, input [2:0] mode, output reg [7:0] Y);
always @* begin
case (mode)
0: Y = A / 8'd0;
1: Y = A % 8'd0;
2: Y = A * 8'd0;
3: Y = A / 8'd1;
4: Y = A % 8'd1;
5: Y = A * 8'd1;
6: Y = A / 8'd2;
7: Y = A % 8'd2;
8: Y = A * 8'd2;
9: Y = A / 8'd4;
10: Y = A % 8'd4;
11: Y = A * 8'd4;
12: Y = A / 8'd8;
13: Y = A % 8'd8;
14: Y = A * 8'd8;
default: Y = 8'd16 * A;
endcase
end
endmodule