Author: Robert Hyatt
Date: 20:24:28 02/28/03
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On February 28, 2003 at 18:00:06, Jeremiah Penery wrote: >http://ccc.it.ro/search/ccc.php?art_id=189071 > >In case the link doesn't work, here's what it says: I'm not sure why this is related. IA64 is non-trivial to optimize for. But not because it has a boatload of registers. For example, use gcc on a sparc and look at the code. With 32 registers, it does quite well and can use 'em all with no problems. I'd be happy to post some sparc .s files if you want to see that this isn't a problem... Now, as for IA64, I have looked at some prelim docs very _lightly_ and it reminds me of other attempts at VLIW computers, with the same bundling difficulties they all had. But this wasn't about IA64 as I was reading it, it was about "large numbers of registers are bad for gcc" and I don't believe that is true in general. > >---- > >Posted by : Eugene Nalimov on September 16, 2001 at 18:07:01 > >Bob, > >Here Vincent is right. GCC core was written in 80's with VAX and 68k as its >primary targets, and it dis not contain optimizations that were unnecessary >than. Developers were able to add some optimizations later, but unfortunately, >to implement some optimizations correctly, total redesign is necessary, and it >was not done (yet?). > >Look, for example, at the minutes of the IA-64 GCC IA-64 Summit >(http://gcc.gnu.org/ml/gcc/2001-06/msg01634.html) for the current state of the >IA-64 gcc port. Compiler is functional, but it produces *very* inefficient code. >Main problem is memory disambiguation (interference information, aliases >analysis). It is very hard to do it properly on GCC's program internal >representation (RTL), as too much information is lost during early compilation >phases. > >Problem affects GCC code quality on all modern CPUs, but it's *vital* for the >IA-64. Vincent is right, the more registers the CPU has, the more severe is the >problem -- to efficiently use large number of registers compiler must have good >interference information. > >Small numbers of registers on x86 helps GCC there, genereated code is suboptimal >due to other reasons. > >Eugene
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