Bug 744

Summary:	llvm expects predicate vectors <N x i1> to have same endianness as byte-endianness
Product:	Libre-SOC's first SoC	Reporter:	Jacob Lifshay <programmerjake>
Component:	Specification	Assignee:	Luke Kenneth Casson Leighton <lkcl>
Status:	CONFIRMED ---
Severity:	enhancement	CC:	libre-soc-isa
Priority:	---
Version:	unspecified
Hardware:	Other
OS:	Linux
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Description Jacob Lifshay 2021-11-10 01:45:43 GMT

llvm expects bit endianness to be identical to byte endianness:
https://github.com/llvm/llvm-project/blob/18334a1c1afe1b8a83c2a6108413bc48d80107df/llvm/lib/Analysis/ConstantFolding.cpp#L218

this will cause problems with big-endian and SV declaring integer predicates to be little-endian (lsb0)

Comment 1 Jacob Lifshay 2021-11-10 01:49:10 GMT

it may be easier for us to just switch predicate endian-ness on big-endian mode rather than add support to llvm for different bit/byte endianness which would require going through a lot of llvm's code.