manually optimized code for 8 bit integer bit reverse builtin, instruction count reduced from 14 to 11, slight performance gain
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The performance implications on PR31810 need to be settled before this can be taken any further
lib/CodeGen/SelectionDAG/LegalizeDAG.cpp | ||
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2613 | This is general legalization code - we should ensure that ISD::ROTL is legalorcustom before attempting this path, otherwise the additional shift/mask code will definitely be a regression. With that in place you can probably drop the VT.isScalarInteger() requirement. | |
test/CodeGen/X86/bitreverse.ll | ||
338 | Please use the update_llc_test_checks.py script |
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The performance measurement testing did not show any performance benefit for the proposed 8bit bit reversal intrinsic implementation over the existing one.