Fix layout for structured buffers of matrices (#1184)

When using row-major layout (via command-line or API option), the following sort of declaration:

```hlsl
StructuredBuffer<float4x4> gBuffer;

... gBuffer[i] ...
```

Generates unexpected results when compiled to DXBC via fxc or DXIL via dxc, because the fxc/dxc compilers do not respect the matrix layout mode in this specific case (a structured buffer of matrices). Instead, they always use column-major layout, even if row-major was requested by the user.

A user can work around this behavior by wrapping the matrix in a `struct`:

```hlsl
struct Wrapper { float4x4 wrapped; }
SturcturedBuffer<Wrapper> gBuffer;

... gBuffer[i].wrapped ...
```

This change simply automates that workaround when compiling for an HLSL-based downstream compiler, so that we get the same behavior across all our backends.

The change adds a test case to confirm the behavior across multiple targets, but it turns out we also had a test checked in that confirmed the buggy (or at least surprising) fxc/dxc behavior, so that one had its baselines changed and can work as a regression test for this fix as well.

1 files changed, 23 insertions, 0 deletions

diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index 2a216994b..6e3ce9c56 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -15,6 +15,7 @@
 #include "slang-ir-ssa.h"
 #include "slang-ir-union.h"
 #include "slang-ir-validate.h"
+#include "slang-ir-wrap-structured-buffers.h"
 #include "slang-legalize-types.h"
 #include "slang-lower-to-ir.h"
 #include "slang-mangle.h"
@@ -384,6 +385,28 @@ Result linkAndOptimizeIR(
 #endif
     validateIRModuleIfEnabled(compileRequest, irModule);
 
+    // For HLSL (and fxc/dxc) only, we need to "wrap" any
+    // structured buffers defined over matrix types so
+    // that they instead use an intermediate `struct`.
+    // This is required to get those targets to respect
+    // the options for matrix layout set via `#pragma`
+    // or command-line options.
+    //
+    switch(target)
+    {
+    case CodeGenTarget::HLSL:
+        {
+            wrapStructuredBuffersOfMatrices(irModule);
+#if 0
+                dumpIRIfEnabled(compileRequest, irModule, "STRUCTURED BUFFERS WRAPPED");
+#endif
+                validateIRModuleIfEnabled(compileRequest, irModule);
+        }
+        break;
+
+    default:
+        break;
+    }
 
     // For GLSL only, we will need to perform "legalization" of
     // the entry point and any entry-point parameters.