Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on February 18, 2013 5:33 pm wrote:
> I don't think you get what I'm saying. Non-compare ALU instructions which set the flags
> are almost exclusively used for equality comparisons. See my other posts with all the
> statistics. That means if you support an adds instruction, setting the single condition
> bit on equality is the correct thing to do as it catches almost all cases.
>
> Of course you have to move the condition field from the branch to compares.
>
> You don't need extra versions of CC setting instructions. Supporting equality alone gets you 94% of cases
> compared to setting 4 condition bits. This can be done by adding a few extra encodings for add/sub/mov
> that set the flag on equal (thus avoiding using a bit on all ALU instructions like most RISCs).
>
> Indeed. Flag setting ALU instructions are just not very useful in general.

And by looking only at GCC you missed a very specifc and yet important case, arbitrary precision arithmetic.

By the numbers you posted on your other post, Alpha did the right thing.