[AIE2P] Add alternative calling convention for library calls #664
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In AIEs default calling convention, all vector registers are caller saved. However, most compiler-rt builtin library functions do not use vector registers. To avoid having to spill vectors to memory in the caller function, we can attach a different calling convention to these library functions.
konstantinschwarz
requested review from
abhinay-anubola,
abnikant,
andcarminati,
F-Stuckmann,
katerynamuts,
khallouh,
martien-de-jong,
niwinanto,
SagarMaheshwari99 and
stephenneuendorffer
as code owners
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This saves up to 512 bytes of stack (ArgMin/ArgMax), and some very minor code size savings. 
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| setLibcallCallingConv(RTLIB::SREM_I32, CallingConv::AIE_PreserveAll_Vec); | ||
| setLibcallCallingConv(RTLIB::SREM_I64, CallingConv::AIE_PreserveAll_Vec); | ||
| setLibcallCallingConv(RTLIB::UREM_I32, CallingConv::AIE_PreserveAll_Vec); | ||
| setLibcallCallingConv(RTLIB::UREM_I64, CallingConv::AIE_PreserveAll_Vec); |
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I see some other libcalls in the LegalizerHelper. Are these only the verified ones?
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Yes, these are only the ones I verified. Others could likely be included as well, but I wanted to keep this limited for now
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In AIEs default calling convention, all vector registers are caller saved. However, most compiler-rt builtin library functions do not use vector registers. To avoid having to spill vectors to memory in the caller function, we can attach a different calling convention to these library functions.
I manually inspected each library function where we apply the alternative calling convention to make sure none of them actually use vector registers. To make this actually save and robust, we should also add a custom calling convention attribute to the frontend that ensures vector registers are actually saved by the callee.