add nvptx_target_feature

Add target features for sm_* and ptx*, both of which form a partial
order, but cannot be combined to a single partial order. These mirror
the LLVM target features, but we do not provide LLVM target
processors (which imply both an sm_* and ptx* feature).

Add some documentation for the nvptx target.

Author: jedbrown

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -271,6 +271,15 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         // Filter out features that are not supported by the current LLVM version
         ("aarch64", "fpmr") => None, // only existed in 18
         ("arm", "fp16") => Some(LLVMFeature::new("fullfp16")),
+        // NVPTX targets added in LLVM 20
+        ("nvptx64", "sm_100") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_100a") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_101") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_101a") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_120") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_120a") if get_version().0 < 20 => None,
+        ("nvptx64", "ptx86") if get_version().0 < 20 => None,
+        ("nvptx64", "ptx87") if get_version().0 < 20 => None,
         // Filter out features that are not supported by the current LLVM version
         ("riscv32" | "riscv64", "zacas") if get_version().0 < 20 => None,
         // Enable the evex512 target feature if an avx512 target feature is enabled.

compiler/rustc_feature/src/unstable.rs

@@ -325,6 +325,7 @@ declare_features! (
     (unstable, m68k_target_feature, "1.85.0", Some(134328)),
     (unstable, mips_target_feature, "1.27.0", Some(44839)),
     (unstable, movrs_target_feature, "CURRENT_RUSTC_VERSION", Some(137976)),
+    (unstable, nvptx_target_feature, "CURRENT_RUSTC_VERSION", Some(44839)),
     (unstable, powerpc_target_feature, "1.27.0", Some(44839)),
     (unstable, prfchw_target_feature, "1.78.0", Some(44839)),
     (unstable, riscv_target_feature, "1.45.0", Some(44839)),

compiler/rustc_span/src/symbol.rs

@@ -1472,6 +1472,7 @@ symbols! {
         not,
         notable_trait,
         note,
+        nvptx_target_feature,
         object_safe_for_dispatch,
         of,
         off,

compiler/rustc_target/src/target_features.rs

@@ -488,6 +488,70 @@ const MIPS_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-end
 ];
 
+const NVPTX_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
+    // tidy-alphabetical-start
+    ("sm_20", Unstable(sym::nvptx_target_feature), &[]),
+    ("sm_21", Unstable(sym::nvptx_target_feature), &["sm_20"]),
+    ("sm_30", Unstable(sym::nvptx_target_feature), &["sm_21"]),
+    ("sm_32", Unstable(sym::nvptx_target_feature), &["sm_30"]),
+    ("sm_35", Unstable(sym::nvptx_target_feature), &["sm_32"]),
+    ("sm_37", Unstable(sym::nvptx_target_feature), &["sm_35"]),
+    ("sm_50", Unstable(sym::nvptx_target_feature), &["sm_37"]),
+    ("sm_52", Unstable(sym::nvptx_target_feature), &["sm_50"]),
+    ("sm_53", Unstable(sym::nvptx_target_feature), &["sm_52"]),
+    ("sm_60", Unstable(sym::nvptx_target_feature), &["sm_53"]),
+    ("sm_61", Unstable(sym::nvptx_target_feature), &["sm_60"]),
+    ("sm_62", Unstable(sym::nvptx_target_feature), &["sm_61"]),
+    ("sm_70", Unstable(sym::nvptx_target_feature), &["sm_62"]),
+    ("sm_72", Unstable(sym::nvptx_target_feature), &["sm_70"]),
+    ("sm_75", Unstable(sym::nvptx_target_feature), &["sm_72"]),
+    ("sm_80", Unstable(sym::nvptx_target_feature), &["sm_75"]),
+    ("sm_86", Unstable(sym::nvptx_target_feature), &["sm_80"]),
+    ("sm_87", Unstable(sym::nvptx_target_feature), &["sm_86"]),
+    ("sm_90", Unstable(sym::nvptx_target_feature), &["sm_87"]),
+    ("sm_90a", Unstable(sym::nvptx_target_feature), &["sm_90"]),
+    // tidy-alphabetical-end
+    // tidy-alphabetical-start
+    ("sm_100", Unstable(sym::nvptx_target_feature), &["sm_90"]),
+    ("sm_100a", Unstable(sym::nvptx_target_feature), &["sm_100"]),
+    ("sm_101", Unstable(sym::nvptx_target_feature), &["sm_100"]),
+    ("sm_101a", Unstable(sym::nvptx_target_feature), &["sm_101"]),
+    ("sm_120", Unstable(sym::nvptx_target_feature), &["sm_101"]),
+    ("sm_120a", Unstable(sym::nvptx_target_feature), &["sm_120"]),
+    // tidy-alphabetical-end
+    // tidy-alphabetical-start
+    ("ptx32", Unstable(sym::nvptx_target_feature), &[]),
+    ("ptx40", Unstable(sym::nvptx_target_feature), &["ptx32"]),
+    ("ptx41", Unstable(sym::nvptx_target_feature), &["ptx40"]),
+    ("ptx42", Unstable(sym::nvptx_target_feature), &["ptx41"]),
+    ("ptx43", Unstable(sym::nvptx_target_feature), &["ptx42"]),
+    ("ptx50", Unstable(sym::nvptx_target_feature), &["ptx43"]),
+    ("ptx60", Unstable(sym::nvptx_target_feature), &["ptx50"]),
+    ("ptx61", Unstable(sym::nvptx_target_feature), &["ptx60"]),
+    ("ptx62", Unstable(sym::nvptx_target_feature), &["ptx61"]),
+    ("ptx63", Unstable(sym::nvptx_target_feature), &["ptx62"]),
+    ("ptx64", Unstable(sym::nvptx_target_feature), &["ptx63"]),
+    ("ptx65", Unstable(sym::nvptx_target_feature), &["ptx64"]),
+    ("ptx70", Unstable(sym::nvptx_target_feature), &["ptx65"]),
+    ("ptx71", Unstable(sym::nvptx_target_feature), &["ptx70"]),
+    ("ptx72", Unstable(sym::nvptx_target_feature), &["ptx71"]),
+    ("ptx73", Unstable(sym::nvptx_target_feature), &["ptx72"]),
+    ("ptx74", Unstable(sym::nvptx_target_feature), &["ptx73"]),
+    ("ptx75", Unstable(sym::nvptx_target_feature), &["ptx74"]),
+    ("ptx76", Unstable(sym::nvptx_target_feature), &["ptx75"]),
+    ("ptx77", Unstable(sym::nvptx_target_feature), &["ptx76"]),
+    ("ptx78", Unstable(sym::nvptx_target_feature), &["ptx77"]),
+    ("ptx80", Unstable(sym::nvptx_target_feature), &["ptx78"]),
+    ("ptx81", Unstable(sym::nvptx_target_feature), &["ptx80"]),
+    ("ptx82", Unstable(sym::nvptx_target_feature), &["ptx81"]),
+    ("ptx83", Unstable(sym::nvptx_target_feature), &["ptx82"]),
+    ("ptx84", Unstable(sym::nvptx_target_feature), &["ptx83"]),
+    ("ptx85", Unstable(sym::nvptx_target_feature), &["ptx84"]),
+    ("ptx86", Unstable(sym::nvptx_target_feature), &["ptx85"]),
+    ("ptx87", Unstable(sym::nvptx_target_feature), &["ptx86"]),
+    // tidy-alphabetical-end
+];
+
 static RISCV_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-start
     ("a", Stable, &["zaamo", "zalrsc"]),
@@ -726,6 +790,7 @@ pub fn all_rust_features() -> impl Iterator<Item = (&'static str, Stability)> {
         .chain(HEXAGON_FEATURES.iter())
         .chain(POWERPC_FEATURES.iter())
         .chain(MIPS_FEATURES.iter())
+        .chain(NVPTX_FEATURES.iter())
         .chain(RISCV_FEATURES.iter())
         .chain(WASM_FEATURES.iter())
         .chain(BPF_FEATURES.iter())
@@ -791,6 +856,7 @@ impl Target {
             "x86" | "x86_64" => X86_FEATURES,
             "hexagon" => HEXAGON_FEATURES,
             "mips" | "mips32r6" | "mips64" | "mips64r6" => MIPS_FEATURES,
+            "nvptx64" => NVPTX_FEATURES,
             "powerpc" | "powerpc64" => POWERPC_FEATURES,
             "riscv32" | "riscv64" => RISCV_FEATURES,
             "wasm32" | "wasm64" => WASM_FEATURES,
@@ -817,6 +883,7 @@ impl Target {
             "sparc" | "sparc64" => SPARC_FEATURES_FOR_CORRECT_VECTOR_ABI,
             "hexagon" => HEXAGON_FEATURES_FOR_CORRECT_VECTOR_ABI,
             "mips" | "mips32r6" | "mips64" | "mips64r6" => MIPS_FEATURES_FOR_CORRECT_VECTOR_ABI,
+            "nvptx64" => &[],      // no vector ABI
             "bpf" | "m68k" => &[], // no vector ABI
             "csky" => CSKY_FEATURES_FOR_CORRECT_VECTOR_ABI,
             // FIXME: for some tier3 targets, we are overly cautious and always give warnings

library/core/src/lib.rs

@@ -190,6 +190,7 @@
 //
 // Target features:
 // tidy-alphabetical-start
+#![cfg_attr(not(bootstrap), feature(nvptx_target_feature))]
 #![feature(aarch64_unstable_target_feature)]
 #![feature(arm_target_feature)]
 #![feature(avx512_target_feature)]

src/doc/rustc/src/platform-support/nvptx64-nvidia-cuda.md

@@ -10,6 +10,40 @@ platform.
 - Riccardo D'Ambrosio, https://github.com/RDambrosio016
 - Kjetil Kjeka, https://github.com/kjetilkjeka
 
+## Requirements
+
+This target is `no_std` and will typically be built with crate-type `cdylib` and `-C linker-flavor=llbc`, which generates PTX.
+The necessary components for this workflow are:
+
+- `rustup toolchain add nightly`
+- `rustup component add llvm-tools --toolchain nightly`
+- `rustup component add llvm-bitcode-linker --toolchain nightly`
+
+There are two options for using the core library:
+
+- `rustup component add rust-src --toolchain nightly` and build using `-Z build-std=core`.
+- `rustup target add nvptx64-nvidia-cuda --toolchain nightly`
+
+### Target and features
+
+It is necessary to specify the target, such as `-C target-cpu=sm_89`. This implies two target features: `sm_89` and `ptx78` (and all preceding features within `sm_*` and `ptx*`). Rust will default to using the oldest PTX version that supports the target processor (see [this table](https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#release-notes-ptx-release-history)), which maximizes driver compatibility.
+One can use `-C target-feature=+ptx80` to choose a later PTX version without changing the target (the default `ptx78` requires CUDA driver version 11.8, while `ptx80` would require driver version 12.0).
+
+Although `ptx*` is represented as a target feature, it is a compile-time property and it is not possible to build a crate that uses instructions not present in the PTX version specified at compile-time (either via `target-cpu` or `target-feature`).
+For example, consider an unaligned barrier `barrier.sync`, which requires both `sm_70` and `ptx60`.
+If one wants to support building for older devices (e.g., `-C target-cpu=sm_62`; ensuring that this unaligned barrier is unreachable at run-time on such devices), the relevant function could use attributes:
+```
+#[cfg(target_feature = "ptx60")]
+#[target_feature(enable = "sm_70")]
+```
+
+## Building Rust kernels
+
+A `no_std` crate containing one or more functions with `extern "ptx-kernel"` can be compiled to PTX using a command like the following.
+
+```console
+$ cargo +nightly rustc --target=nvptx64-nvidia-cuda -Zbuild-std=core --crate-type=cdylib -- -Clinker-flavor=llbc -Ctarget-cpu=sm_89 -Zunstable-options
+```
 <!-- FIXME: fill this out
 
 ## Requirements

tests/ui/target-feature/gate.rs

@@ -7,6 +7,7 @@
 // gate-test-arm_target_feature
 // gate-test-hexagon_target_feature
 // gate-test-mips_target_feature
+// gate-test-nvptx_target_feature
 // gate-test-wasm_target_feature
 // gate-test-adx_target_feature
 // gate-test-cmpxchg16b_target_feature