[Serialization] Replace fixed-width fields with smaller VBR fields #26887
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VBR fields can store up to 64 bits of info in N-bit units, where the top bit describes whether there are further units to come. See http://llvm.org/docs/BitCodeFormat.html for more information. In the cases of the fields changed here, these are all usually-small values that can /occasionally/ get a lot larger; a VBR field allows us to pick a reasonable default while still not setting a maximum. Swiftmodule size micro-optimization. No functionality change; due to LLVM bitstream being a self-describing container format, this does not actually break compatibility.
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varungandhi-apple
approved these changes
Aug 27, 2019
rjmccall
approved these changes
Aug 28, 2019
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VBR fields can store up to 64 bits of info in N-bit units, where the top bit describes whether there are further units to come. See http://llvm.org/docs/BitCodeFormat.html for more information. In the cases of the fields changed here, these are all usually-small values that can occasionally get a lot larger; a VBR field allows us to pick a reasonable default while still not setting a maximum.
Swiftmodule size micro-optimization. No functionality change; due to LLVM bitstream being a self-describing container format, this does not actually break compatibility.