Precompiled SPIR-V import support (#5048)

* Precompiled SPIR-V import support

Adds appropriate linkage and function declaration syntax
for SPIR-V functions that are declared, to be imported
from another SPIR-V module.

Unlike DXIL, stripping the Slang IR for a function down
to a declaration requires retaining a block of parameters,
as the function declaration must be emitted to SPIR-V
with the same parameters as a definition. Because that
thwarts the logic in Slang to tell the difference between
a declaration and definition, and explicit decoration is
introduced to explicitly mark functions which need to be
treated as declarations during emit phase.

Fixes #4992

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/source/slang/slang-ir-redundancy-removal.cpp b/source/slang/slang-ir-redundancy-removal.cpp
index 230f356a4..b90a8705d 100644
--- a/source/slang/slang-ir-redundancy-removal.cpp
+++ b/source/slang/slang-ir-redundancy-removal.cpp
@@ -171,6 +171,7 @@ bool removeRedundancyInFunc(IRGlobalValueWithCode* func)
 void removeAvailableInDownstreamModuleDecorations(CodeGenTarget target, IRModule* module)
 {
     List<IRInst*> toRemove;
+    auto builder = IRBuilder(module);
     for (auto globalInst : module->getGlobalInsts())
     {
         if (auto funcInst = as<IRFunc>(globalInst))
@@ -181,13 +182,11 @@ void removeAvailableInDownstreamModuleDecorations(CodeGenTarget target, IRModule
                     (dec->getTarget() == target))
                 {
                     // Gut the function definition, turning it into a declaration
-                    for (auto inst : funcInst->getChildren())
+                    for (auto block : funcInst->getBlocks())
                     {
-                        if (inst->getOp() == kIROp_Block)
-                        {
-                            toRemove.add(inst);
-                        }
+                        toRemove.add(block);
                     }
+                    builder.addDecoration(funcInst, kIROp_DownstreamModuleImportDecoration);
                 }
             }
         }