Add a flag to control type splitting

The `-split-mixed-types` flag can be provided to command-line `slangc`, and the `SLANG_COMPILE_FLAG_SPLIT_MIXED_TYPE` flag can be passed to `spSetCompileFlags`.
Either of these turns on a mode where Slang will split types that included both resource and non-resource fields.
The declaration of such a type will just drop the resource fields, while a variable declare using such a type turns into multiple declararations: one for the non-resource fields, and then one for each resource field (recursively).

This behavior was already implemented for GLSL support, and this change just adds a flag so that the user can turn it on unconditionally.

Caveats:

- This does not apply in "full rewriter" mode, which is what happens if the user doesn't use any `import`s. I could try to fix that, but it seems like in that mode people are asking to bypass as much of the compiler as possible.

- When it *does* apply, it applies to user code as well as library/Slang code. So this will potentially rewrite the user's own HLSL in ways they wouldn't expect. I don't see a great way around it, though.

2 files changed, 15 insertions, 0 deletions

diff --git a/source/slang/lower.cpp b/source/slang/lower.cpp
index 7a12fc3b7..70c153902 100644
--- a/source/slang/lower.cpp
+++ b/source/slang/lower.cpp
@@ -2833,6 +2833,17 @@ struct LoweringVisitor
             // due to, e.g., bindless textures.
             shouldDesugarTupleTypes = true;
         }
+        else if( shared->compileRequest->compileFlags & SLANG_COMPILE_FLAG_SPLIT_MIXED_TYPES )
+        {
+            // If the user is directly asking us to do this transformation,
+            // then obviously we need to do it.
+            //
+            // TODO: The way this is defined here means it will even apply to user
+            // HLSL code (not just code written in Slang). We may want to
+            // reconsider that choice, and only split things that originated in Slang.
+            //
+            shouldDesugarTupleTypes = true;
+        }
 
         bool isResultATupleType = false;
         bool hasAnyNonTupleFields = false;
diff --git a/source/slang/options.cpp b/source/slang/options.cpp
index a360695f2..0e329ccd2 100644
--- a/source/slang/options.cpp
+++ b/source/slang/options.cpp
@@ -254,6 +254,10 @@ struct OptionsParser
                 //else
                 if (argStr == "-no-checking")
                     flags |= SLANG_COMPILE_FLAG_NO_CHECKING;
+                else if(argStr == "-split-mixed-types" )
+                {
+                    flags |= SLANG_COMPILE_FLAG_SPLIT_MIXED_TYPES;
+                }
                 else if (argStr == "-backend" || argStr == "-target")
                 {
                     String name = tryReadCommandLineArgument(arg, &argCursor, argEnd);