Fixes 574. Eliminate empty structs during type legalization (shader-slang#577)

Author: csyonghe

source/slang/ir-legalize-types.cpp

@@ -818,6 +818,8 @@ static LegalVal legalizeInst(
             args,
             inst->getOperandCount());
 
+    case kIROp_undefined:
+        return LegalVal();
     default:
         // TODO: produce a user-visible diagnostic here
         SLANG_UNEXPECTED("non-simple operand(s)!");

source/slang/legalize-types.cpp

@@ -301,6 +301,12 @@ struct TupleTypeBuilder
 
     LegalType getResult()
     {
+        // If this is an empty struct, return a none type
+        // This helps get rid of emtpy structs that often trips up the 
+        // downstream compiler
+        if (!anyOrdinary && !anySpecial && !anyComplex)
+            return LegalType::tuple(new TuplePseudoType());
+
         // If we didn't see anything "special"
         // then we can use the type as-is.
         // we can conceivably just use the type as-is

tests/compute/empty-struct.slang

@@ -0,0 +1,19 @@
+//TEST(smoke,compute):COMPARE_COMPUTE:
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+// Confirm that generics syntax can be used in user
+// code and generates valid output.
+
+RWStructuredBuffer<float> outputBuffer;
+
+struct Simple
+{
+    float getVal() {return 1.0;}
+};
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    Simple s;
+	float outVal = s.getVal();
+	outputBuffer[dispatchThreadID.x] = outVal;
+}

tests/compute/empty-struct.slang.expected.txt

@@ -0,0 +1,4 @@
+3F800000
+3F800000
+3F800000
+3F800000