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[ARM] Some processors appear to have optional features enabled by default #113008

Open alexrp opened 2 hours ago

alexrp commented 2 hours ago

See this Zig pull request: https://github.com/ziglang/zig/pull/18498 (specifically, this hunk)

It seems that LLVM is enabling features for these processors that are actually optional, per Arm documentation. We're currently working around this in Zig by omitting these features by default in the Zig CPU model/feature data which is sourced from LLVM's.

Would there be interest in a patch to similarly disable these features by default on the LLVM side?

(Note: Please ignore the addition of trustzone to cortex-m85; as discussed in #109770, this was based on a misunderstanding and has since been reverted.)

llvmbot commented 2 hours ago

@llvm/issue-subscribers-backend-arm

Author: Alex Rønne Petersen (alexrp)

See this Zig pull request: https://github.com/ziglang/zig/pull/18498 (specifically, [this hunk](https://github.com/ziglang/zig/pull/18498/files#diff-88edb24013ad7e5428ff29aac0ebba01f919136cfcfe17d806b1892b2af7d065R382-R404)) It seems that LLVM is enabling features for these processors that are actually optional, per Arm documentation. We're currently working around this in Zig by omitting these features by default in the Zig CPU model/feature data which is sourced from LLVM's. Would there be interest in a patch to similarly disable these features by default on the LLVM side? (Note: Please ignore the addition of `trustzone` to `cortex-m85`; as discussed in #109770, this was based on a misunderstanding and has since been reverted.)