[MLton-devel] Extra instruction in (n div 2)

[Tom Murphy]

The code "n div 2" is compiled to this:

        movl %edx,%ecx
        sarl $0,%ecx
        shrl $31,%ecx
        addl %ecx,%edx
        sarl $1,%edx

The second instruction is a no-op -- a shift by zero doesn't even affect
the flags.


This can be fixed by changing
mlton/codegen/x86-codegen/x86-simplify.fun:1599 from:

   => if i > 0
       (* then emit sar instruction with count i - 1 *)

to

   => if i > 1


 - Tom

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