dawn_native: Add a force_wgsl_step toggle.

This makes SPIRV ingestion always go through a SPIRV->WGSL step first.
This will be used to make sure that path works correctly on existing
WebGPU SPIRV sites so we're confident the SPIRV->WGSL translation will
work when compiled to WASM.

Bug: dawn:960
Change-Id: I17efd8c64d9d60ff033ba89b8fff9295e66524ef
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/56080
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: Corentin Wallez <cwallez@chromium.org>

build_overrides/tint.gni

@@ -14,10 +14,9 @@
 
 tint_root_dir = "//third_party/tint"
 tint_spirv_tools_dir = "//third_party/vulkan-deps/spirv-tools/src"
-tint_googletest_dir = "//third_party/googletest"
 tint_spirv_headers_dir = "//third_party/vulkan-deps/spirv-headers/src"
 
 tint_build_spv_reader = true
 tint_build_spv_writer = true
 tint_build_wgsl_reader = true
-tint_build_wgsl_writer = false
+tint_build_wgsl_writer = true

src/dawn_native/ShaderModule.cpp

@@ -1086,6 +1086,30 @@ namespace dawn_native {
         const ShaderModuleWGSLDescriptor* wgslDesc = nullptr;
         FindInChain(chainedDescriptor, &wgslDesc);
 
+        // We have a temporary toggle to force the SPIRV ingestion to go through a WGSL
+        // intermediate step. It is done by switching the spirvDesc for a wgslDesc below.
+        ShaderModuleWGSLDescriptor newWgslDesc;
+        std::string newWgslCode;
+        if (spirvDesc && device->IsToggleEnabled(Toggle::ForceWGSLStep)) {
+            std::vector<uint32_t> spirv(spirvDesc->code, spirvDesc->code + spirvDesc->codeSize);
+            tint::Program program;
+            DAWN_TRY_ASSIGN(program, ParseSPIRV(spirv, outMessages));
+
+            tint::writer::wgsl::Generator generator(&program);
+            if (!generator.Generate()) {
+                std::ostringstream errorStream;
+                errorStream << "Tint WGSL failure:" << std::endl;
+                errorStream << "Generator: " << generator.error() << std::endl;
+                return DAWN_VALIDATION_ERROR(errorStream.str().c_str());
+            }
+
+            newWgslCode = generator.result();
+            newWgslDesc.source = newWgslCode.c_str();
+
+            spirvDesc = nullptr;
+            wgslDesc = &newWgslDesc;
+        }
+
         if (spirvDesc) {
             if (device->IsToggleEnabled(Toggle::DisallowSpirv)) {
                 return DAWN_VALIDATION_ERROR("SPIR-V is disallowed.");

src/dawn_native/Toggles.cpp

@@ -194,7 +194,13 @@ namespace dawn_native {
               "Dump generated shaders for debug propose, dumped shaders will be log via "
               "EmitLog, thus printed in Chrome console or consumed by user-defined callback "
               "function.",
-              "https://crbug.com/dawn/792"}}
+              "https://crbug.com/dawn/792"}},
+            {Toggle::ForceWGSLStep,
+             {"force_wgsl_step",
+              "When ingesting SPIR-V shaders, force a first conversion to WGSL. This allows "
+              "testing Tint's SPIRV->WGSL translation on real content to be sure that it will "
+              "work when the same translation runs in a WASM module in the page.",
+              "https://crbug.com/dawn/960"}},
             // Dummy comment to separate the }} so it is clearer what to copy-paste to add a toggle.
         }};
     }  // anonymous namespace

src/dawn_native/Toggles.h

@@ -54,6 +54,7 @@ namespace dawn_native {
         EmitHLSLDebugSymbols,
         DisallowSpirv,
         DumpTranslatedShaders,
+        ForceWGSLStep,
 
         EnumCount,
         InvalidEnum = EnumCount,