Add RISC-V platform and PAUSE instruction

.github/workflows/main.yml

@@ -72,6 +72,7 @@ jobs:
         - arm-unknown-linux-gnueabihf
         - armv7-unknown-linux-gnueabihf
         - aarch64-unknown-linux-gnu
+        - riscv64gc-unknown-linux-gnu
         - powerpc64le-unknown-linux-gnu
         - mips-unknown-linux-gnu
         - mips64-unknown-linux-gnuabi64

crates/core_arch/src/core_arch_docs.md

@@ -185,6 +185,7 @@ others at:
 * [`x86_64`]
 * [`arm`]
 * [`aarch64`]
+* [`riscv`]
 * [`mips`]
 * [`mips64`]
 * [`powerpc`]
@@ -196,6 +197,7 @@ others at:
 [`x86_64`]: x86_64/index.html
 [`arm`]: arm/index.html
 [`aarch64`]: aarch64/index.html
+[`riscv`]: riscv/index.html
 [`mips`]: mips/index.html
 [`mips64`]: mips64/index.html
 [`powerpc`]: powerpc/index.html

crates/core_arch/src/mod.rs

@@ -55,6 +55,16 @@ pub mod arch {
         pub use crate::core_arch::aarch64::*;
     }
 
+    /// Platform-specific intrinsics for the `riscv` platform.
+    ///
+    /// See the [module documentation](../index.html) for more details.
+    #[cfg(any(target_arch = "riscv32", target_arch = "riscv64", doc))]
+    #[doc(cfg(any(target_arch = "riscv32", target_arch = "riscv64")))]
+    #[unstable(feature = "stdsimd", issue = "27731")]
+    pub mod riscv {
+        pub use crate::core_arch::riscv::*;
+    }
+
     /// Platform-specific intrinsics for the `wasm32` platform.
     ///
     /// This module provides intrinsics specific to the WebAssembly
@@ -251,6 +261,10 @@ mod aarch64;
 #[doc(cfg(any(target_arch = "arm")))]
 mod arm;
 
+#[cfg(any(target_arch = "riscv32", target_arch = "riscv64", doc))]
+#[doc(cfg(any(target_arch = "riscv32", target_arch = "riscv64")))]
+mod riscv;
+
 #[cfg(any(target_family = "wasm", doc))]
 #[doc(cfg(target_family = "wasm"))]
 mod wasm32;

crates/core_arch/src/riscv/mod.rs

@@ -0,0 +1,10 @@
+//! RISC-V intrinsics
+
+/// Generates the `PAUSE` instruction
+/// 
+/// The PAUSE instruction is a HINT that indicates the current hart's rate of instruction retirement
+/// should be temporarily reduced or paused. The duration of its effect must be bounded and may be zero.
+#[inline(always)]
+pub unsafe fn pause() {
+    asm!(".word 0x0100000F")
+}