Fix a bug in struct inheritance (#1861)

During lowering from AST to IR, the Slang compiler translates code that uses `struct` inheritance:

```hlsl
struct Base { int a; }
struct Derived : Base {}
```

into code where the inheritance relationship is "witnessed" by a simple field:

```hlsl
struct Base { int a; }
struct Derived { Base __anonymous_field__; }
```

The underlying bug here is that the `__anonymous_field__` that the compiler generated during IR lowering was not being given any linkage decorations (no mangled name). As a result, if multiple separately-compiled modules all access that field they could disagree on its identity as an IR instruction. This could lead to output code being generated where the declaration of `__anonymous_field__` uses one IR instruction, but accesses use another.

This change includes a fix for the issue, and a test that serves as a reproducer for the original problem.

2 files changed, 10 insertions, 0 deletions

diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index 74b11079d..16164b957 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -698,6 +698,15 @@ Result linkAndOptimizeIR(
     // bit_cast on basic types.
     lowerBitCast(targetRequest, irModule);
     eliminateDeadCode(irModule);
+
+
+    // We include one final step to (optionally) dump the IR and validate
+    // it after all of the optimization passes are complete. This should
+    // reflect the IR that code is generated from as closely as possible.
+    //
+#if 0
+    dumpIRIfEnabled(compileRequest, irModule, "OPTIMIZED");
+#endif
     validateIRModuleIfEnabled(compileRequest, irModule);
 
     return SLANG_OK;
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index de5a07c0d..ab488a41f 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -5475,6 +5475,7 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
                 // a field that holds the base type...
                 //
                 auto irKey = getBuilder()->createStructKey();
+                addLinkageDecoration(context, irKey, inheritanceDecl);
                 auto keyVal = LoweredValInfo::simple(irKey);
                 setGlobalValue(context, inheritanceDecl, keyVal);
                 return keyVal;