chandlerc, 4 months ago

Is there a good reason #LLVM targeting #AArch64 doesn't seem to fold shifts into operands when it would require shifting in multiple operands?

I'm seeing lots of:

lsr xN, xN, #7  
and x?, x?, xN  
...  
and x?, x?, xN  

With no other uses of xN.

Is there a reason to prefer this over:

and x?, x?, xN, lsr #7  
...  
and x?, x?, xN, lsr #7  

While "duplicated", it seems like it would save an instruction at least in decode?