Support __target_intrinsic modifiers in IR codegen (#401)

The standard library already has a bunch of these decorations, since they were added to support Slang->Vulkan codegen on the AST-to-AST path. This change makes the IR code generator able to exploit the modifiers so that we pick up a bunch of Vulkan support "for free" in the short term.

The basic change is in `lower-to-ir.cpp` where we copy over any `TargetIntrinsicModifier`s to become `IRTargetIntrinsicDecoration`s with the same information. We then need a bit of logic in `ir.cpp` to make sure we clone them as needed.

The core work of using the modifiers is in `emit.cpp`, where I basically just copy-pasted the existing logic that applied in the AST path (all the AST-related code there is dead, and we should clean it up soon).

The big change that comes with this logic is that when dealing with a member function, the numbering of the argument used in the intrinsic definition string changes, so that `$0` refers to the base object (whereas before the base object was looked up via the base expression of a `MemberExpr` used for the function). This requires a bunch of the definitions in the library to be updated; hopefully I caught them all.

For kicks, I've re-enabled a cross-compilation test just to confirm that we are generating valid SPIR-V for code that performs texture-fetch operations. I don't expect us to keep that test enabled as-is in the long term, though, because it would be much better to instead use render-test to do the same thing. Alas, beefing up the Vulkan support in render-test is an outstanding work item, and I didn't want to pollute this change with more work along those lines.

1 files changed, 18 insertions, 0 deletions

diff --git a/source/slang/lower-to-ir.cpp b/source/slang/lower-to-ir.cpp
index 4eb762333..bde50aa89 100644
--- a/source/slang/lower-to-ir.cpp
+++ b/source/slang/lower-to-ir.cpp
@@ -3757,6 +3757,24 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
             decoration->targetName = targetMod->targetToken.Content;
         }
 
+        // If this declaration was marked as having a target-specific lowering
+        // for a particular target, then handle that here.
+        for (auto targetMod : decl->GetModifiersOfType<TargetIntrinsicModifier>())
+        {
+            auto decoration = getBuilder()->addDecoration<IRTargetIntrinsicDecoration>(irFunc);
+            decoration->targetName = targetMod->targetToken.Content;
+
+            auto definitionToken = targetMod->definitionToken;
+            if (definitionToken.type == TokenType::StringLiteral)
+            {
+                decoration->definition = getStringLiteralTokenValue(definitionToken);
+            }
+            else
+            {
+                decoration->definition = definitionToken.Content;
+            }
+        }
+
         // For convenience, ensure that any additional global
         // values that were emitted while outputting the function
         // body appear before the function itself in the list