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Re-enable atomic loads and stores for all RISC-V targets
This roughly reverts PR #66548 Atomic "CAS" are still disabled for targets without the *“A” Standard Extension for Atomic Instructions*. However this extension only adds instructions for operations more complex than simple loads and stores, which are always atomic when aligned. In the [Unprivileged Spec v. 20191213](https://riscv.org/technical/specifications/) section 2.6 *Load and Store Instructions* of chapter 2 *RV32I Base Integer Instruction Set* (emphasis mine): > Even when misaligned loads and stores complete successfully, > these accesses might run extremely slowly depending on the implementation > (e.g., when implemented via an invisible trap). Further-more, whereas > **naturally aligned loads and stores are guaranteed to execute atomically**, > misaligned loads and stores might not, and hence require > additional synchronization to ensure atomicity. Unfortunately PR #66548 did not provide much details on the bug that motivated it, but #66240 and #85736 appear related and happen with targets that do have the A extension.
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