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4 Commits

Author SHA1 Message Date
whitequark bf8db55ef3 opt_expr: improve simplification of comparisons with large constants. 
The idea behind this simplification is that a N-bit signal X being
compared with an M-bit constant where M>N and the constant has Nth
or higher bit set, it either always succeeds or always fails.

However, the existing implementation only worked with one-hot signals
for some reason. It also printed incorrect messages.

This commit adjusts the simplification to have as much power as
possible, and fixes other bugs.
 2019-01-02 15:45:28 +00:00
whitequark 4fd458290c opt_expr: refactor simplification of unsigned X<onehot and X>=onehot. NFCI. 2019-01-02 05:11:29 +00:00
whitequark 9e9846a6ea opt_expr: refactor simplification of signed X>=0 and X<0. NFCI. 2019-01-02 03:01:25 +00:00
whitequark 8e53d2e0bf opt_expr: simplify any unsigned comparisons with all-0 and all-1. 
Before this commit, only unsigned comparisons with all-0 would be
simplified. This commit also makes the code handling such comparisons
to be more rigorous and not abort on unexpected input.
 2019-01-02 02:45:49 +00:00