Introduce TARGET fallbacks in CMake #1752
Conversation
X86(-64) targets for cross-compilation are likely to be for a simulator/testing and not a production environment. Regardless, we do not know information about the target yet, so choose a default of core2/penryn.
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I am not sure if this premise is correct, and I expect the performance hit from using old kernels on new hardware would be much more noticable than on ARM. Perhaps just expanding the error message with a hint on exactly how to specify the TARGET to cmake would be better ? |
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Well that's why I originally left it empty because we cannot work out what hardware it will be targeting automatically. |
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Maybe I am confused, but isn't the hunter ticket you linked to about cross-compiling from (whatever) to ARMV8 anyway ? And your emulator target scenario may be likely when the cross-compiler name suggests an Android NDK or the IOS equivalent coupled with x86 hardware (but I am not sure it would make sense to try to parse all that in the cmake file), but less so for general Linux/Windows cross builds. |
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No there is no issue on arm cause we can just target v8 or v7 and done. |
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Alright, but how do we (or rather cmake) know someone wants to target IOS or Android simulator, rather than just cross-compile for a production environment with different OS ? |
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If it is iOS and x86, it has to be the simulator. |
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X86 default is overly modern. While good for current 32bit windows (which you really dont simulate test much), modern 32bit linux would base at pentium or pentimpro (no MMX) |
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As stated above I am not convinced we would want a fallback for x86 at all, where both the variety of targets and the loss of performance from choosing a lowest common denominator would be much greater than on other the other supported architectures. |
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Indeed. Better to bail out early and get cpuid via bug report |
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As I understand it this is about cross-compiling where there is no chance to autodetect the target platform, so it would be "tell them how to name their target to cmake" with no need for a bug report or cpuid. |
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How about if we detect iOS and x86_64, we use a sane default? They likely won't care about performance so much for simulator. |
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I disagree with statement about minimal specification in emulator. Look no further than qemu and intel SDE. |
X86(-64) targets for cross-compilation are likely to be for a simulator/testing and not a production environment. Regardless, we do not know information about the target yet, so choose a default of core2/penryn.