From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Date: Fri, 25 May 2012 19:13:31 -0700 > One issue is just syntactic: the fact that you want to initialize > those constants just results in nasty syntax. Is gcc really so bad on > sparc that it doesn't do the obvious CSE etc on the constants? That > surprises me, because it does it on x86-64.. It CSE's them into the loop, but like I said a few days ago it doesn't CSE them into the find_zero() code block. > Do you *really* need to CSE them by hand? Yes, GCC refused to do it. It CSEs it into the loop, but not the tail code. > So how bad does the code look on sparc if you just get rid of the > "low_bits" and "high_bits" and just replace them with the constants > they are? It looks like GCC reconstituting the constants for the zero byte determination, which on 64-bit is nearly half of the instructions of the exit path. But you shouldn't really need to care about this, we can surely abstract it behind something. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
