Fix handling of z_digit "?" and fix optimization of cmp with "z" #1377
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Signed-off-by: Clifford Wolf <clifford@clifford.at>
whitequark
reviewed
Sep 13, 2019
| @@ -953,6 +953,10 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons | |||
| } | |||
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| if (b.is_fully_const()) { | |||
| if (b.is_fully_undef()) { | |||
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Should this be is_fully_undef and not is_any_undef? My reading of the standard is that any x or z bits in any operand cause the result to be x.
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This code is only for 1 bit expressions, so fully_undef and any_undef is the same.. However, answering the more general point, for example 2'b00 == 2'b1x is 1'b0. That's what's meant by "if [...] the relation is ambiguous".
whitequark
approved these changes
Sep 14, 2019
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See m-labs/nmigen#202 (comment) for details.