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>

1 files changed, 13 insertions, 0 deletions

diff --git a/source/compiler-core/slang-downstream-compiler.h b/source/compiler-core/slang-downstream-compiler.h
index 82aaef107..c96003cc4 100644
--- a/source/compiler-core/slang-downstream-compiler.h
+++ b/source/compiler-core/slang-downstream-compiler.h
@@ -343,6 +343,19 @@ public:
 
     /// 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