|Re: [eigen] vectorization and ABI|
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Hi, sorry, I didn't explain my idea well enough. I think that it is quick to implement, does not lengthen compilation, does not require macros, and adds only 1 line of code all in all. *** what we currently do **** in util/Constants.h : #ifdef EIGEN_VECTORIZE const unsigned int PacketAccessBit = 0x8; #else const unsigned int PacketAccessBit = 0x0; #endif in other files: Flags = PacketAccessBit | SomeMoreBits; ... if(Flags & PacketAccessBit) ... *** what I propose instead *** in util/Constants.h : const unsigned int PacketAccessBit = 0x8; #ifdef EIGEN_VECTORIZE const unsigned int ActualPacketAccess = PacketAccessBit ; #else const unsigned int PacketAccessBit = 0x0; #endif in other files: // just replace PacketAccessBit by ActualPacketAccess and you're done Flags = ActualPacketAccess | SomeMoreBits; ... if(Flags & ActualPacketAccess) ... *** That's it. Do you like it? As you can see it's just search and replace plus one line to add in util/Constants.h. Benoit On Thursday 03 July 2008 10:22:11 Gael Guennebaud wrote: > Hi, > > I'm not sure to understand what you wanna do with ActualPacketAccess, > but I see at least two other workarounds: > > - using preprocessor #if/#endif directives in Assign.h (and everywhere > we enable vectorization) > > - using a macro or a meta structure to get the actual value of > Flags&PacketAccessBit...for instance: > instead for writing : Derived::Flags&PacketAccessBit you would write: > EI_HAS_PACKET_ACCESS(Derived) > > and currently I'm in favor of such a macro: easy to use, no > compilation time penalty. > > cheers, > gael. > > On Thu, Jul 3, 2008 at 8:57 AM, Benoît Jacob <jacob@xxxxxxxxxxxxxxx> wrote: > > Hi, > > > > I think again that we need to make sure that enabling/disabling > > vectorization does not affect the ABI. The use case is for apps who want > > to make a runtime switch for vectorization. They would compile the same > > file a.cpp with and without -msse2. If a.cpp contains functions that take > > (refs to) Eigen matrices as argument, this requires the type of Eigen > > matrices to be independent of whether -msse2 is used. This is currently > > not the case since PacketAccessBit is set to 0 unless vectorization is > > enabled. So I think we must change that. I understand that setting > > PacketAccessBit to 0 was a nice convenience to quickly ensure that > > vectorized paths are never used without vectorization support, but we can > > do without... so I'm for setting PacketAccessBit regardless of the > > vectorization switch; and we could have another constant > > ActualPacketAccess that is the same thing that is currently called > > PacketAccessBit. What do you think? I know we discussed that before but I > > don't remember clearly the outcome. > > > > Cheers, > > > > Benoit
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