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Consistent $mux undef handling

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* Change simlib's $mux cell to use the ternary operator as $_MUX_
  already does
* Stop opt_expr -keepdc from changing S=x to S=0
* Change const eval of $mux and $pmux to match the updated simlib
  (fixes sim)
* The sat behavior of $mux already matches the updated simlib

The verilog frontend uses $mux for the ternary operators and this
changes all interpreations of the $mux cell (that I found) to match the
verilog simulation behavior for the ternary operator. For 'if' and
'case' expressions the frontend may also use $mux but uses $eqx if the
verilog simulation behavior is requested with the '-ifx' option.

For $pmux there is a remaining mismatch between the sat behavior and the
simlib behavior. Resolving this requires more discussion, as the $pmux
cell does not directly correspond to a specific verilog construct.
This commit is contained in:
Jannis Harder 2022-10-21 15:41:20 +02:00
parent 4f4cff0080
commit c77b7343d0
5 changed files with 38 additions and 15 deletions
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2
passes/opt/opt_expr.cc
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@ -1494,7 +1494,7 @@ skip_identity:
RTLIL::SigSpec input = assign_map(cell->getPort(ID::S));
RTLIL::SigSpec inA = assign_map(cell->getPort(ID::A));
RTLIL::SigSpec inB = assign_map(cell->getPort(ID::B));
if (input.is_fully_const())
if (input.is_fully_const() && (!keepdc || input.is_fully_def()))
ACTION_DO(ID::Y, input.as_bool() ? cell->getPort(ID::B) : cell->getPort(ID::A));
else if (inA == inB)
ACTION_DO(ID::Y, cell->getPort(ID::A));