[PATCH] D61052: [compiler-rt][builtins] Implement some fetch-and-x operations for Cortex-M

[Oliver Stannard (Linaro) via Phabricator via llvm-commits]

ostannard added a comment.

> The instruction exists on A-class targets. It's just that on most A-class targets, we run in userspace, and userspace isn't allowed to disable interrupts, for obvious reasons.

M-profile also has two privilege levels, and the CPS instruction is not usable in unprivileged mode, so disabling interrupts won't always work (and the CPS instruction is a no-op in unprivileged mode, so we would silently get non-atomic accesses).


Repository:
  rCRT Compiler Runtime

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  https://reviews.llvm.org/D61052/new/

https://reviews.llvm.org/D61052