[spirv] Add support for casting from floatM to floatMx1 (#3905)

Fixes #3893

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -2567,9 +2567,9 @@ SpirvInstruction *SpirvEmitter::doCastExpr(const CastExpr *expr) {
     return doExpr(subExpr);
   }
   case CastKind::CK_HLSLVectorToMatrixCast: {
-    // If target type is already an 1xN matrix type, we just return the
+    // If target type is already an 1xN or Mx1 matrix type, we just return the
     // underlying vector.
-    if (is1xNMatrix(toType))
+    if (is1xNMatrix(toType) || isMx1Matrix(toType))
       return doExpr(subExpr);
 
     // A vector can have no more than 4 elements. The only remaining case

tools/clang/test/CodeGenSPIRV/cast.vec-to-mat.implicit.hlsl

@@ -0,0 +1,21 @@
+// Run: %dxc -T ps_6_0 -E main
+
+float4 main(float4 input : A) : SV_Target {
+// CHECK:       [[vec:%\d+]] = OpConstantComposite %v4float %float_1 %float_2 %float_3 %float_4
+// CHECK:                      OpStore %var1 [[vec]]
+	float4 var1 = float4(1,2,3,4);
+
+// CHECK-NEXT: [[vec1:%\d+]] = OpLoad %v4float %var1
+// CHECK-NEXT:                 OpStore %var2 [[vec1]]
+	float4x1 var2 = var1;
+
+// CHECK-NEXT:      [[vec2:%\d+]] = OpLoad %v4float %input
+// CHECK-NEXT:                 OpStore %var3 [[vec2]]
+	float1x4 var3 = input;
+
+// CHECK-NEXT: [[vec3:%\d+]] = OpLoad %v4float %input
+// CHECK-NEXT:                 OpStore %var4 [[vec3]]
+	float4x1 var4 = input;
+
+    return input;
+}

tools/clang/unittests/SPIRV/CodeGenSpirvTest.cpp

@@ -478,6 +478,9 @@ TEST_F(FileTest, CastFlatConversionDecomposeVector) {
 TEST_F(FileTest, CastExplicitVecToMat) {
   runFileTest("cast.vec-to-mat.explicit.hlsl");
 }
+TEST_F(FileTest, CastImplicitVecToMat) {
+  runFileTest("cast.vec-to-mat.implicit.hlsl");
+}
 TEST_F(FileTest, CastMatrixToVector) { runFileTest("cast.mat-to-vec.hlsl"); }
 TEST_F(FileTest, CastBitwidth) { runFileTest("cast.bitwidth.hlsl"); }