On Tue, Aug 28, 2012 at 11:48 AM, JMGross <msp...@grossibaer.de> wrote: > > I think it's a flaw in the compiler that it doesn't use BIS Rx, &y for an |= > instruction where the result of the right-side value is in Rx. > It only does so if the rvalue is a compile-time constant. [...] > There is apparently still some room for improvements.
Yes. > I guess (and it's only a guess) that the compiler will also push > parameters on stack by loading them into a register and pushing the > register instead of just pushing the immediate value or the > memory content to the stack. No. I really don't understand why you create and publish fantasies like this about things that mspgcc might do poorly but doesn't. "But I said it was a guess!" is an unworthy excuse for somebody with your reputation. Since it takes you about thirty seconds to create the FUD and takes me significant effort to rebut it, I'm not going to even try. I'll just make my annual plea that folks remember: JM's expertise on the MSP430 itself is unquestioned, but he doesn't know how today's mspgcc works and unless things have changed doesn't even use it. You're probably best off ignoring what he guesses about how it might behave. [...] > Nobody denied that. Only operations with an rvalue that has no > volatile parts could be made atomic. And apparently only constant > rvalues lead to an atomic operation with the current compiler version. Not true. See my previous email for the mechanism by which this is done, and run some experiments to see the situations where it's successful and where it isn't. If it isn't, look for intervening instructions from complex calculation of the RHS that prevent recognition of read-modify-write pattern expected by the the peephole optimization. It's pretty easy to come up with an example where a register RHS is applied in a single instruction even in the current compiler, and only slightly harder to trick the compiler into making the right choice in other cases too (hint: volatile local variable named "rhs"). That the optimization can apply less frequently with 20120406 than with 20110716 is unfortunate, but suboptimal code is preferable to incorrect code, and mspgcc up through 20110716 managed volatiles incorrectly. Peter ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Mspgcc-users mailing list Mspgcc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mspgcc-users
