wgsl: add spirv-unknown-wgsl target, transpiling with naga

Author: Firestar99

Cargo.lock

@@ -59,6 +59,9 @@ impl SpirvTargetEnv {
             SpirvTargetEnv::Vulkan_1_4 => {
                 include_str!("../target-specs/spirv-unknown-vulkan1.4.json")
             }
+            SpirvTargetEnv::Wgsl => {
+                include_str!("../target-specs/spirv-unknown-wgsl.json")
+            }
         }
     }
 }

crates/rustc_codegen_spirv-target-specs/src/include_str.rs

@@ -58,6 +58,8 @@ pub enum SpirvTargetEnv {
     Vulkan_1_3,
     #[strum(to_string = "vulkan1.4")]
     Vulkan_1_4,
+    #[strum(to_string = "wgsl")]
+    Wgsl,
 }
 
 #[derive(Error)]

crates/rustc_codegen_spirv-target-specs/src/lib.rs

@@ -0,0 +1,26 @@
+{
+  "allows-weak-linkage": false,
+  "arch": "spirv",
+  "crt-objects-fallback": "false",
+  "crt-static-allows-dylibs": true,
+  "data-layout": "e-m:e-p:32:32:32-i64:64-n8:16:32:64",
+  "dll-prefix": "",
+  "dll-suffix": ".spv.json",
+  "dynamic-linking": true,
+  "emit-debug-gdb-scripts": false,
+  "env": "wgsl",
+  "linker-flavor": "unix",
+  "linker-is-gnu": false,
+  "llvm-target": "spirv-unknown-wgsl",
+  "main-needs-argc-argv": false,
+  "metadata": {
+    "description": null,
+    "host_tools": null,
+    "std": null,
+    "tier": null
+  },
+  "os": "unknown",
+  "panic-strategy": "abort",
+  "simd-types-indirect": false,
+  "target-pointer-width": "32"
+}

crates/rustc_codegen_spirv-target-specs/target-specs/spirv-unknown-wgsl.json

@@ -60,6 +60,7 @@ itertools = "0.10.5"
 tracing.workspace = true
 tracing-subscriber.workspace = true
 tracing-tree = "0.3.0"
+naga = { version = "25.0.1", features = ["spv-in", "wgsl-out"] }
 
 # required for cargo gpu to resolve the needed target specs
 rustc_codegen_spirv-target-specs.workspace = true

crates/rustc_codegen_spirv/Cargo.toml

@@ -129,6 +129,7 @@ mod custom_decorations;
 mod custom_insts;
 mod link;
 mod linker;
+mod naga_transpile;
 mod spirv_type;
 mod spirv_type_constraints;
 mod symbols;

crates/rustc_codegen_spirv/src/lib.rs

@@ -2,6 +2,7 @@
 use crate::maybe_pqp_cg_ssa as rustc_codegen_ssa;
 
 use crate::codegen_cx::{CodegenArgs, SpirvMetadata};
+use crate::naga_transpile::should_transpile;
 use crate::{SpirvCodegenBackend, SpirvModuleBuffer, SpirvThinBuffer, linker};
 use ar::{Archive, GnuBuilder, Header};
 use rspirv::binary::Assemble;
@@ -311,6 +312,10 @@ fn post_link_single_module(
 
         drop(save_modules_timer);
     }
+
+    if let Some(transpile) = should_transpile(sess) {
+        transpile(sess, cg_args, &spv_binary, out_filename).ok();
+    }
 }
 
 fn do_spirv_opt(

crates/rustc_codegen_spirv/src/link.rs

@@ -0,0 +1,75 @@
+use crate::codegen_cx::CodegenArgs;
+use rustc_codegen_spirv_target_specs::SpirvTargetEnv;
+use rustc_session::Session;
+use rustc_span::ErrorGuaranteed;
+use std::path::Path;
+
+pub type NagaTranspile = fn(
+    sess: &Session,
+    cg_args: &CodegenArgs,
+    spv_binary: &[u32],
+    out_filename: &Path,
+) -> Result<(), ErrorGuaranteed>;
+
+pub fn should_transpile(sess: &Session) -> Option<NagaTranspile> {
+    let target = SpirvTargetEnv::parse_triple(sess.opts.target_triple.tuple())
+        .expect("parsing should fail earlier");
+    match target {
+        SpirvTargetEnv::Wgsl => Some(transpile::wgsl_transpile),
+        _ => None,
+    }
+}
+
+mod transpile {
+    use crate::codegen_cx::CodegenArgs;
+    use naga::error::ShaderError;
+    use naga::valid::Capabilities;
+    use rustc_session::Session;
+    use rustc_span::ErrorGuaranteed;
+    use std::path::Path;
+
+    pub fn wgsl_transpile(
+        sess: &Session,
+        _cg_args: &CodegenArgs,
+        spv_binary: &[u32],
+        out_filename: &Path,
+    ) -> Result<(), ErrorGuaranteed> {
+        // these should be params via spirv-builder
+        let opts = naga::front::spv::Options::default();
+        let capabilities = Capabilities::default();
+        let writer_flags = naga::back::wgsl::WriterFlags::empty();
+
+        let module = naga::front::spv::parse_u8_slice(bytemuck::cast_slice(spv_binary), &opts)
+            .map_err(|err| {
+                sess.dcx()
+                    .err(format!("Naga failed to parse spv: \n{}", ShaderError {
+                        source: String::new(),
+                        label: None,
+                        inner: Box::new(err),
+                    }))
+            })?;
+        let mut validator =
+            naga::valid::Validator::new(naga::valid::ValidationFlags::default(), capabilities);
+        let info = validator.validate(&module).map_err(|err| {
+            sess.dcx()
+                .err(format!("Naga validation failed: \n{}", ShaderError {
+                    source: String::new(),
+                    label: None,
+                    inner: Box::new(err),
+                }))
+        })?;
+
+        let wgsl_dst = out_filename.with_extension("wgsl");
+        let wgsl = naga::back::wgsl::write_string(&module, &info, writer_flags).map_err(|err| {
+            sess.dcx()
+                .err(format!("Naga failed to write wgsl : \n{}", err))
+        })?;
+
+        std::fs::write(&wgsl_dst, wgsl).map_err(|err| {
+            sess.dcx()
+                .err(format!("failed to write wgsl to file: {}", err))
+        })?;
+
+        Ok(())
+    }
+}

crates/rustc_codegen_spirv/src/naga_transpile.rs

@@ -33,6 +33,8 @@ impl TargetsExt for SpirvTargetEnv {
             | SpirvTargetEnv::Vulkan_1_2
             | SpirvTargetEnv::Vulkan_1_3
             | SpirvTargetEnv::Vulkan_1_4 => MemoryModel::Vulkan,
+
+            SpirvTargetEnv::Wgsl => MemoryModel::Vulkan,
         }
     }
 
@@ -57,6 +59,8 @@ impl TargetsExt for SpirvTargetEnv {
             SpirvTargetEnv::Vulkan_1_2 => spirv_tools::TargetEnv::Vulkan_1_2,
             SpirvTargetEnv::Vulkan_1_3 => spirv_tools::TargetEnv::Vulkan_1_3,
             SpirvTargetEnv::Vulkan_1_4 => spirv_tools::TargetEnv::Vulkan_1_4,
+
+            SpirvTargetEnv::Wgsl => spirv_tools::TargetEnv::Vulkan_1_2,
         }
     }