[CombFolds] Don't canonicalize extract(shl(1, x)) if shift is multiply used #7527
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…y used There is a canonicalization for `exract(c, shl(1, x))` to `x == c` but this canonicalization introduces a bunch of comparision to constants. This harms PPA when bitwidth is large (e.g. 16 bit shift introduce 2^16 icmp op). To prevent such regressions this commit imposes restriction regarding the number of uses for shift.
seldridge
approved these changes
Aug 19, 2024
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There are substantial changes in output verilog but all of them are expected changes. The change should preserve a design intent of one-hot encoding in a much better way. |
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There is a canonicalization for
exract(c, shl(1, x))tox == cbut this canonicalization introduces a bunch of comparision to constants. This harms PPA when bitwidth is large (e.g. 16 bit shift introduce 2^16 icmp op). To prevent such regressions this commit imposes restriction regarding the number of uses for shift.