Correctly handle comma operator w/matrices (#3921)

The special HLSL matrix codegen didn't handle the comma operator. Since
the operation is simple enough, skip special handling and fallback to
the default behavior

Fixed #3916

tools/clang/lib/CodeGen/CGExprScalar.cpp

@@ -204,17 +204,16 @@ public:
     if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(E)) {
       if (hlsl::IsHLSLMatType(E->getType()) ||
           hlsl::IsHLSLMatType(BinOp->getLHS()->getType())) {
-          if (BinOp->getOpcode() != BO_Assign) {
-              llvm::Value *LHS = CGF.EmitScalarExpr(BinOp->getLHS());
-              llvm::Value *RHS = CGF.EmitScalarExpr(BinOp->getRHS());
-              return CGF.CGM.getHLSLRuntime().EmitHLSLMatrixOperationCall(
-                  CGF, E, ConvertType(E->getType()), { LHS, RHS });
-          }
-          else {
+          if (BinOp->getOpcode() == BO_Assign) {
               LValue LHS = CGF.EmitLValue(BinOp->getLHS());
               llvm::Value *RHS = CGF.EmitScalarExpr(BinOp->getRHS());
               CGF.CGM.getHLSLRuntime().EmitHLSLMatrixStore(CGF, RHS, LHS.getAddress(), BinOp->getLHS()->getType());
               return RHS;
+          } else if (BinOp->getOpcode() != BO_Comma) { // comma handled by standard Visit below
+              llvm::Value *LHS = CGF.EmitScalarExpr(BinOp->getLHS());
+              llvm::Value *RHS = CGF.EmitScalarExpr(BinOp->getRHS());
+              return CGF.CGM.getHLSLRuntime().EmitHLSLMatrixOperationCall(
+                  CGF, E, ConvertType(E->getType()), { LHS, RHS });
           }
       }
     } else if (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(E)) {

tools/clang/test/HLSLFileCheck/hlsl/types/matrix/matrix_comma.hlsl

@@ -0,0 +1,29 @@
+// RUN: %dxc -E vecret -T ps_6_0 %s | FileCheck %s
+// RUN: %dxc -T lib_6_3 %s | FileCheck %s -check-prefix=CHK_MAT
+
+// verify that the comma operator works with matrix types
+
+// CHECK: dx.op.loadInput
+// CHECK-NEXT: dx.op.loadInput
+// CHECK-NEXT: dx.op.loadInput
+// CHECK-NEXT: dx.op.loadInput
+
+// CHECK-NEXT: dx.op.storeOutput
+// CHECK-NEXT: dx.op.storeOutput
+// CHECK-NEXT: dx.op.storeOutput
+// CHECK-NEXT: dx.op.storeOutput
+
+// CHK_MAT: store %class.matrix.float.2.2
+// CHK_MAT: load %class.matrix.float.2.2
+
+// Check where the result IS NOT a matrix type
+float4 vecret(float2x2 pmat : M, float4 pvec : V) : SV_Target {
+  return pmat , pvec;
+}
+
+// Check where the result IS a matrix type
+export
+float2x2 matret(float2x2 pmat : M, float4 pvec : V) {
+  return pmat;
+}
+