[PATCH] D116088: [compiler-rt] Implement ARM atomic operations for architectures without SMP support

[Eli Friedman via Phabricator via cfe-commits]

efriedma added a comment.

In D116088#3534100 <https://reviews.llvm.org/D116088#3534100>, @kpdev42 wrote:

> 1. Sets memory barrier
> 2. Calls atomic load from memory location
> 3. Modifies data
> 4. Calls atomic store to memory location
> 5. Checks that operation is consistent, if not goes to step 2.
>
> Now if we are on a platform which doesn't support SMP we can use ordinary memory operations instead
> of atomic ones, can't we?

Even on a non-SMP processor, there's a bit of magic in ldrex/strex: ldrex sets a hidden "lock" bit, and strex checks it.  If there's a context switch between the load and the store, the switch will clear that bit.  So when the code continues to execute, the store fails.


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https://reviews.llvm.org/D116088