On Thu, Oct 13, 2011 at 2:30 PM, Richard Kenner <ken...@vlsi1.ultra.nyu.edu> wrote: >> It is because mask 0xffffffff is optimized to 0xfffffffc by keeping track >> of non-zero bits in registers and the above code doesn't take that >> into account. > > Then I'd suggest modifying that code so that it does rather than > essentially duplicating it. But I'd recommend running some > performance tests to verify that you're not pessimizing things when > you do that: this stuff can be very tricky and you want to make sure > that you're not converting something like (and X 3) into a bit > extraction unnecessarily. >
But the current code converts (and X 3) into a bit extraction since ((i = exact_log2 (UINTVAL (XEXP (x, 1)) + 1)) >= 0) is true when UINTVAL (XEXP (x, 1)) == 3. Should we do it or not? -- H.J.
