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https://rise4fun.com/Alive/8BY - valid for lshr+trunc+variable sext https://rise4fun.com/Alive/7jk - the variable sext can be redundant https://rise4fun.com/Alive/Qslu - 'exact'-ness of first shift can be preserver https://rise4fun.com/Alive/IF63 - without trunc we could view this as more general "drop redundant mask before right-shift", but let's handle it here for now https://rise4fun.com/Alive/iip - likewise, without trunc, variable sext can be redundant. There's more patterns for sure - e.g. we can have 'lshr' as the final shift, but that might be best handled by some more generic transform, e.g. "drop redundant masking before right-shift" (PR42456) I'm singling-out this sext patch because you can only extract high bits with `*shr` (unlike abstract bit masking), and i *know* this fold is wanted by existing code. I don't believe there is much to review here, so i'm gonna opt into post-review mode here. https://bugs.llvm.org/show_bug.cgi?id=43523 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373542 91177308-0d34-0410-b5e6-96231b3b80d8
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