Rollup merge of #91548 - luojia65:hint-spin-loop-riscv, r=Amanieu

Add spin_loop hint for RISC-V architecture

This commit uses the PAUSE instruction (https://github.com/rust-lang/stdarch/pull/1262) to implement RISC-V spin loop, and updates `stdarch` submodule to use the merged PAUSE instruction.

2 files changed, 5 insertions, 0 deletions

diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index 95798879155..f49aefea81b 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -137,6 +137,11 @@ pub fn spin_loop() {
             unsafe { crate::arch::arm::__yield() };
         }
     }
+
+    #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
+    {
+        crate::arch::riscv::pause();
+    }
 }
 
 /// An identity function that *__hints__* to the compiler to be maximally pessimistic about what
diff --git a/library/stdarch b/library/stdarch
-Subproject cfba59fccd90b3b52a614120834320f764ab08d
+Subproject b70ae88ef2a6c83acad0a1e83d5bd78f9655fd0