Thanks for this! I'm wary of the duplication being added here though, and amode rules are some of the most sensitive in Cranelift so we ideally want as little duplication as possible. For example the offset=0 rules are duplicates of above rules, and even using AMode.UnsignedOffset is a duplicate of prior rules as well. Would it be possible to shuffle rules around and add if-let clauses perhaps to tweak existing rules? For example rules could use if-let or some sort of extraction matcher to ensure that offset is 0. Either that or the rule using AMode.UnsignedOffset could be given higher priority.

For example the offset=0 rules are duplicates of above rules, and even using AMode.UnsignedOffset is a duplicate of prior rules as well. Would it be possible to shuffle rules around and add if-let clauses perhaps to tweak existing rules? For example rules could use if-let or some sort of extraction matcher to ensure that offset is 0. Either that or the rule using AMode.UnsignedOffset could be given higher priority.

I have removed the duplication. Also added uimm12_scaled_nonzero_from_i64 (+ its verifier spec) so rules 8/9's UnsignedOffset only matches non-zero offsets and takes higher priority than 4/5; a zero offset falls through to the existing RegExtended rules naturally.

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cc @cfallin, @fitzgen

This helps remove some duplication, yeah, but this is still effectively a duplication of rule (2), however, and it's also a duplication of 3/4/5 in terms of matching pattern. My thinking is that what you want can be achieved by raising the priority of rule 2 because the premise here is that the static offset should have the highest priority for getting folded into the instruction itself while leaving all other computations in a CSE-able form.

This helps remove some duplication, yeah, but this is still effectively a duplication of rule (2), however, and it's also a duplication of 3/4/5 in terms of matching pattern. My thinking is that what you want can be achieved by raising the priority of rule 2 because the premise here is that the static offset should have the highest priority for getting folded into the instruction itself while leaving all other computations in a CSE-able form.

It's done! I have replaced the four rules with a single generic highest-priority UnsignedOffset rule (non-zero uimm12), so it's rule 2's action raised in priority with no pattern duplication. Zero offsets fall through to the reg-folding rules. It also now folds plain-iadd/scaled cases, dropping an instruction in one amodes.clif function.