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, 10 insertions, 1 deletions

diff --git a/tools/gfx-unit-test/gfx-test-util.cpp b/tools/gfx-unit-test/gfx-test-util.cpp
index 2bbe65416..d7cfa0f65 100644
--- a/tools/gfx-unit-test/gfx-test-util.cpp
+++ b/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);