Add extract-over-extend simplification for partial-width extracts - #800
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the-mr-dave wants to merge 2 commits into
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Add extract-over-extend simplification for partial-width extracts#800the-mr-dave wants to merge 2 commits into
the-mr-dave wants to merge 2 commits into
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sign_extend/zero_extend only add bits above the original value, so extracting bits [hi:0] where hi falls anywhere between the original width and the full extended width always gives back a smaller extend of the original value (or the original value itself, if no padding bits survive). Co-authored-by: rvinton <rvinton@users.noreply.github.com>
Covers extract fully undoing an extend, partial reduction (extract width between the original and the fully extended width), and the two guard cases where the rule must not apply (extract of the full extended width, extract of a plain variable). Co-authored-by: rvinton <rvinton@users.noreply.github.com>
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Summary
extracting bits [hi:0] where hi falls between the original width and the
full extended width always gives back a smaller extend of the original
value (or the original value itself, if no padding bits survive).
cases (extract of the full extended width, extract of a plain variable)
that must not trigger the rule.