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Re: CSE not combining equivalent expressions.
> I'm not immediately aware of too many cases where lowering the IL is
> going to expose new opportunities to track and optimize nonzero/zero
> bits stuff.
Bitfield are the big one. If you have both bitfield and logical operations,
you can often merge the logical operations with those used to retrieve
and/or store the field.
Things such as
x.y |= 1;
where Y is a bitfield and X non-BLKmode would be a large sequence of logical
operations that can all be replaced by a single OR insn at the RTL level
but presents no optimization opportunities at the tree level.