Support SPIR-V deferred linking option (#6500)

The new option "SkipDownstreamLinking" will defer final downstream IR
linking to the user application. This option only has an effect if
there are modules that were precompiled to the target IR using
precompileForTarget().

Until now, the default behavior for SPIR-V was to use deferred linking, and
the default behavior for DXIL was to use immediate/internal linking in Slang.

This change only affects the SPIR-V behavior such that both deferred and
non-deferred linking is supported based on the new option.

To support the non-deferred option, Slang will internally call into
SPIRV-Tools-link to reconstitute a complete SPIR-V shader program when
necessary (due to modules having been precompiled to target IR).
Otherwise, if SkipDownstreamLinking is enabled, the shader returned by
e.g. getTargetCode() or getEntryPointCode() may have import linkage to
the SPIR-V embedded in the constituent modules.

Closes #4994

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

Author: cheneym2

include/slang-gfx.h

@@ -163,6 +163,12 @@ class IShaderProgram : public ISlangUnknown
         SeparateEntryPointCompilation
     };
 
+    enum class DownstreamLinkMode
+    {
+        None,
+        Deferred,
+    };
+
     struct Desc
     {
         // TODO: Tess doesn't like this but doesn't know what to do about it
@@ -180,6 +186,9 @@ class IShaderProgram : public ISlangUnknown
         // An array of Slang entry points. The size of the array must be `entryPointCount`.
         // Each element must define only 1 Slang EntryPoint.
         slang::IComponentType** slangEntryPoints = nullptr;
+
+        // Indicates whether the app is responsible for final downstream linking.
+        DownstreamLinkMode downstreamLinkMode = DownstreamLinkMode::None;
     };
 
     struct CreateDesc2

include/slang.h

@@ -653,6 +653,7 @@ typedef uint32_t SlangSizeT;
         SLANG_PASS_THROUGH_SPIRV_OPT,     ///< SPIRV-opt
         SLANG_PASS_THROUGH_METAL,         ///< Metal compiler
         SLANG_PASS_THROUGH_TINT,          ///< Tint WGSL compiler
+        SLANG_PASS_THROUGH_SPIRV_LINK,    ///< SPIRV-link
         SLANG_PASS_THROUGH_COUNT_OF,
     };
 
@@ -1008,6 +1009,8 @@ typedef uint32_t SlangSizeT;
 
         EmitReflectionJSON, // bool
         SaveGLSLModuleBinSource,
+
+        SkipDownstreamLinking, // bool, experimental
         CountOf,
     };
 

source/compiler-core/slang-downstream-compiler.h

@@ -343,6 +343,19 @@ class IDownstreamCompiler : public ICastable
 
     /// True if underlying compiler uses file system to communicate source
     virtual SLANG_NO_THROW bool SLANG_MCALL isFileBased() = 0;
+
+    virtual SLANG_NO_THROW int SLANG_MCALL link(
+        const uint32_t** modules,
+        const uint32_t* moduleSizes,
+        const uint32_t moduleCount,
+        IArtifact** outArtifact)
+    {
+        SLANG_UNREFERENCED_PARAMETER(modules);
+        SLANG_UNREFERENCED_PARAMETER(moduleSizes);
+        SLANG_UNREFERENCED_PARAMETER(moduleCount);
+        SLANG_UNREFERENCED_PARAMETER(outArtifact);
+        return 0;
+    }
 };
 
 class DownstreamCompilerBase : public ComBaseObject, public IDownstreamCompiler

source/compiler-core/slang-glslang-compiler.cpp

@@ -49,6 +49,11 @@ class GlslangDownstreamCompiler : public DownstreamCompilerBase
     validate(const uint32_t* contents, int contentsSize) SLANG_OVERRIDE;
     virtual SLANG_NO_THROW SlangResult SLANG_MCALL
     disassemble(const uint32_t* contents, int contentsSize) SLANG_OVERRIDE;
+    int link(
+        const uint32_t** modules,
+        const uint32_t* moduleSizes,
+        const uint32_t moduleCount,
+        IArtifact** outArtifact) SLANG_OVERRIDE;
 
     /// Must be called before use
     SlangResult init(ISlangSharedLibrary* library);
@@ -66,6 +71,7 @@ class GlslangDownstreamCompiler : public DownstreamCompilerBase
     glslang_CompileFunc_1_2 m_compile_1_2 = nullptr;
     glslang_ValidateSPIRVFunc m_validate = nullptr;
     glslang_DisassembleSPIRVFunc m_disassemble = nullptr;
+    glslang_LinkSPIRVFunc m_link = nullptr;
 
     ComPtr<ISlangSharedLibrary> m_sharedLibrary;
 
@@ -80,6 +86,7 @@ SlangResult GlslangDownstreamCompiler::init(ISlangSharedLibrary* library)
     m_validate = (glslang_ValidateSPIRVFunc)library->findFuncByName("glslang_validateSPIRV");
     m_disassemble =
         (glslang_DisassembleSPIRVFunc)library->findFuncByName("glslang_disassembleSPIRV");
+    m_link = (glslang_LinkSPIRVFunc)library->findFuncByName("glslang_linkSPIRV");
 
     if (m_compile_1_0 == nullptr && m_compile_1_1 == nullptr && m_compile_1_2 == nullptr)
     {
@@ -323,6 +330,32 @@ SlangResult GlslangDownstreamCompiler::disassemble(const uint32_t* contents, int
     return SLANG_FAIL;
 }
 
+SlangResult GlslangDownstreamCompiler::link(
+    const uint32_t** modules,
+    const uint32_t* moduleSizes,
+    const uint32_t moduleCount,
+    IArtifact** outArtifact)
+{
+    glslang_LinkRequest request;
+    memset(&request, 0, sizeof(request));
+
+    request.modules = modules;
+    request.moduleSizes = moduleSizes;
+    request.moduleCount = moduleCount;
+
+    if (!m_link(&request))
+    {
+        return SLANG_FAIL;
+    }
+
+    auto artifact = ArtifactUtil::createArtifactForCompileTarget(SLANG_SPIRV);
+    artifact->addRepresentationUnknown(
+        Slang::RawBlob::create(request.linkResult, request.linkResultSize * sizeof(uint32_t)));
+
+    *outArtifact = artifact.detach();
+    return SLANG_OK;
+}
+
 bool GlslangDownstreamCompiler::canConvert(const ArtifactDesc& from, const ArtifactDesc& to)
 {
     // Can only disassemble blobs that are SPIR-V
@@ -467,6 +500,14 @@ SlangResult SpirvDisDownstreamCompilerUtil::locateCompilers(
     return locateGlslangSpirvDownstreamCompiler(path, loader, set, SLANG_PASS_THROUGH_SPIRV_DIS);
 }
 
+SlangResult SpirvLinkDownstreamCompilerUtil::locateCompilers(
+    const String& path,
+    ISlangSharedLibraryLoader* loader,
+    DownstreamCompilerSet* set)
+{
+    return locateGlslangSpirvDownstreamCompiler(path, loader, set, SLANG_PASS_THROUGH_SPIRV_LINK);
+}
+
 #else // SLANG_ENABLE_GLSLANG_SUPPORT
 
 /* static */ SlangResult GlslangDownstreamCompilerUtil::locateCompilers(

source/compiler-core/slang-glslang-compiler.h

@@ -32,6 +32,14 @@ struct SpirvDisDownstreamCompilerUtil
         DownstreamCompilerSet* set);
 };
 
+struct SpirvLinkDownstreamCompilerUtil
+{
+    static SlangResult locateCompilers(
+        const String& path,
+        ISlangSharedLibraryLoader* loader,
+        DownstreamCompilerSet* set);
+};
+
 } // namespace Slang
 
 #endif

source/slang-glslang/slang-glslang.cpp

@@ -1037,7 +1037,7 @@ extern "C"
             request->linkResultSize = linkedBinary.size();
         }
 
-        return success;
+        return success == SPV_SUCCESS;
     }
     catch (...)
     {

source/slang/slang-compiler.cpp

@@ -2669,6 +2669,12 @@ bool CodeGenContext::shouldDumpIR()
     return getTargetProgram()->getOptionSet().getBoolOption(CompilerOptionName::DumpIr);
 }
 
+bool CodeGenContext::shouldSkipDownstreamLinking()
+{
+    return getTargetProgram()->getOptionSet().getBoolOption(
+        CompilerOptionName::SkipDownstreamLinking);
+}
+
 bool CodeGenContext::shouldReportCheckpointIntermediates()
 {
     return getTargetProgram()->getOptionSet().getBoolOption(

source/slang/slang-compiler.h

@@ -1384,7 +1384,8 @@ enum class PassThroughMode : SlangPassThroughIntegral
     LLVM = SLANG_PASS_THROUGH_LLVM,                  ///< LLVM 'compiler'
     SpirvOpt = SLANG_PASS_THROUGH_SPIRV_OPT,         ///< pass thorugh spirv to spirv-opt
     MetalC = SLANG_PASS_THROUGH_METAL,
-    Tint = SLANG_PASS_THROUGH_TINT, ///< pass through spirv to Tint API
+    Tint = SLANG_PASS_THROUGH_TINT,            ///< pass through spirv to Tint API
+    SpirvLink = SLANG_PASS_THROUGH_SPIRV_LINK, ///< pass through spirv to spirv-link
     CountOf = SLANG_PASS_THROUGH_COUNT_OF,
 };
 void printDiagnosticArg(StringBuilder& sb, PassThroughMode val);
@@ -2886,6 +2887,12 @@ struct CodeGenContext
     // removed between IR linking and target source generation.
     bool removeAvailableInDownstreamIR = false;
 
+    // Determines if program level compilation like getTargetCode() or getEntryPointCode()
+    // should return a fully linked downstream program or just the glue SPIR-V/DXIL that
+    // imports and uses the precompiled SPIR-V/DXIL from constituent modules.
+    // This is a no-op if modules are not precompiled.
+    bool shouldSkipDownstreamLinking();
+
 protected:
     CodeGenTarget m_targetFormat = CodeGenTarget::Unknown;
     ExtensionTracker* m_extensionTracker = nullptr;

source/slang/slang-emit.cpp

@@ -2093,10 +2093,71 @@ SlangResult emitSPIRVForEntryPointsDirectly(
     if (compiler)
     {
 #if 0
-        // Dump the unoptimized SPIRV after lowering from slang IR -> SPIRV
+        // Dump the unoptimized/unlinked SPIRV after lowering from slang IR -> SPIRV
         compiler->disassemble((uint32_t*)spirv.getBuffer(), int(spirv.getCount() / 4));
 #endif
 
+        bool isPrecompilation = codeGenContext->getTargetProgram()->getOptionSet().getBoolOption(
+            CompilerOptionName::EmbedDownstreamIR);
+
+        if (!isPrecompilation && !codeGenContext->shouldSkipDownstreamLinking())
+        {
+            ComPtr<IArtifact> linkedArtifact;
+
+            // collect spirv files
+            List<uint32_t*> spirvFiles;
+            List<uint32_t> spirvSizes;
+
+            // Start with the SPIR-V we just generated.
+            // SPIRV-Tools-link expects the size in 32-bit words
+            // whereas the spirv blob size is in bytes.
+            spirvFiles.add((uint32_t*)spirv.getBuffer());
+            spirvSizes.add(int(spirv.getCount()) / 4);
+
+            // Iterate over all modules in the linkedIR. For each module, if it
+            // contains an embedded downstream ir instruction, add it to the list
+            // of spirv files.
+            auto program = codeGenContext->getProgram();
+
+            program->enumerateIRModules(
+                [&](IRModule* irModule)
+                {
+                    for (auto globalInst : irModule->getModuleInst()->getChildren())
+                    {
+                        if (auto inst = as<IREmbeddedDownstreamIR>(globalInst))
+                        {
+                            if (inst->getTarget() == CodeGenTarget::SPIRV)
+                            {
+                                auto slice = inst->getBlob()->getStringSlice();
+                                spirvFiles.add((uint32_t*)slice.begin());
+                                spirvSizes.add(int(slice.getLength()) / 4);
+                            }
+                        }
+                    }
+                });
+
+            SLANG_ASSERT(int(spirv.getCount()) % 4 == 0);
+            SLANG_ASSERT(spirvFiles.getCount() == spirvSizes.getCount());
+
+            if (spirvFiles.getCount() > 1)
+            {
+                SlangResult linkresult = compiler->link(
+                    (const uint32_t**)spirvFiles.getBuffer(),
+                    (const uint32_t*)spirvSizes.getBuffer(),
+                    (uint32_t)spirvFiles.getCount(),
+                    linkedArtifact.writeRef());
+
+                if (linkresult != SLANG_OK)
+                {
+                    return SLANG_FAIL;
+                }
+
+                ComPtr<ISlangBlob> blob;
+                linkedArtifact->loadBlob(ArtifactKeep::No, blob.writeRef());
+                artifact = _Move(linkedArtifact);
+            }
+        }
+
         if (!codeGenContext->shouldSkipSPIRVValidation())
         {
             StringBuilder runSpirvValEnvVar;

tools/gfx-unit-test/gfx-test-util.cpp

@@ -80,7 +80,8 @@ Slang::Result loadComputeProgram(
     Slang::ComPtr<gfx::IShaderProgram>& outShaderProgram,
     const char* shaderModuleName,
     const char* entryPointName,
-    slang::ProgramLayout*& slangReflection)
+    slang::ProgramLayout*& slangReflection,
+    PrecompilationMode precompilationMode)
 {
     Slang::ComPtr<slang::IBlob> diagnosticsBlob;
     slang::IModule* module = slangSession->loadModule(shaderModuleName, diagnosticsBlob.writeRef());
@@ -115,6 +116,14 @@ Slang::Result loadComputeProgram(
 
     gfx::IShaderProgram::Desc programDesc = {};
     programDesc.slangGlobalScope = composedProgram.get();
+    if (precompilationMode == PrecompilationMode::ExternalLink)
+    {
+        programDesc.downstreamLinkMode = gfx::IShaderProgram::DownstreamLinkMode::Deferred;
+    }
+    else
+    {
+        programDesc.downstreamLinkMode = gfx::IShaderProgram::DownstreamLinkMode::None;
+    }
 
     auto shaderProgram = device->createProgram(programDesc);
 

tools/gfx-unit-test/gfx-test-util.h

@@ -7,6 +7,13 @@
 
 namespace gfx_test
 {
+enum class PrecompilationMode
+{
+    None,
+    SlangIR,
+    InternalLink,
+    ExternalLink,
+};
 /// Helper function for print out diagnostic messages output by Slang compiler.
 void diagnoseIfNeeded(slang::IBlob* diagnosticsBlob);
 
@@ -24,7 +31,8 @@ Slang::Result loadComputeProgram(
     Slang::ComPtr<gfx::IShaderProgram>& outShaderProgram,
     const char* shaderModuleName,
     const char* entryPointName,
-    slang::ProgramLayout*& slangReflection);
+    slang::ProgramLayout*& slangReflection,
+    PrecompilationMode precompilationMode = PrecompilationMode::None);
 
 Slang::Result loadComputeProgramFromSource(
     gfx::IDevice* device,