[spirv] Support struct -> struct FlatConversion.

tools/clang/test/CodeGenSPIRV/cast.flat-conversion.no-op.struct.hlsl

@@ -0,0 +1,60 @@
+// Run: %dxc -T cs_6_0 -E main
+
+// Processing FlatConversion when source and destination
+// are both structures with identical members.
+
+struct FirstStruct {
+  float3 anArray[4];
+  float2x3 mats[1];
+  int2 ints[3];
+};
+
+struct SecondStruct {
+  float3 anArray[4];
+  float2x3 mats[1];
+  int2 ints[3];
+};
+
+RWStructuredBuffer<FirstStruct> rwBuf : register(u0);
+[ numthreads ( 16 , 16 , 1 ) ]
+void main() {
+  SecondStruct values;
+  FirstStruct v;
+
+// Yes, this is a FlatConversion!
+// CHECK:      [[v0ptr:%\d+]] = OpAccessChain %_ptr_Function__arr_v3float_uint_4_0 %values %int_0
+// CHECK-NEXT:    [[v0:%\d+]] = OpLoad %_arr_v3float_uint_4_0 [[v0ptr]]
+// CHECK-NEXT: [[v1ptr:%\d+]] = OpAccessChain %_ptr_Function__arr_mat2v3float_uint_1_0 %values %int_1
+// CHECK-NEXT:    [[v1:%\d+]] = OpLoad %_arr_mat2v3float_uint_1_0 [[v1ptr]]
+// CHECK-NEXT: [[v2ptr:%\d+]] = OpAccessChain %_ptr_Function__arr_v2int_uint_3_0 %values %int_2
+// CHECK-NEXT:    [[v2:%\d+]] = OpLoad %_arr_v2int_uint_3_0 [[v2ptr]]
+// CHECK-NEXT:     [[v:%\d+]] = OpCompositeConstruct %FirstStruct_0 [[v0]] [[v1]] [[v2]]
+// CHECK-NEXT:                  OpStore %v [[v]]
+  v = values;
+
+// CHECK:          [[v0ptr:%\d+]] = OpAccessChain %_ptr_Function__arr_v3float_uint_4_0 %values %int_0
+// CHECK-NEXT:        [[v0:%\d+]] = OpLoad %_arr_v3float_uint_4_0 [[v0ptr]]
+// CHECK-NEXT:     [[v1ptr:%\d+]] = OpAccessChain %_ptr_Function__arr_mat2v3float_uint_1_0 %values %int_1
+// CHECK-NEXT:        [[v1:%\d+]] = OpLoad %_arr_mat2v3float_uint_1_0 [[v1ptr]]
+// CHECK-NEXT:     [[v2ptr:%\d+]] = OpAccessChain %_ptr_Function__arr_v2int_uint_3_0 %values %int_2
+// CHECK-NEXT:        [[v2:%\d+]] = OpLoad %_arr_v2int_uint_3_0 [[v2ptr]]
+// CHECK-NEXT:    [[values:%\d+]] = OpCompositeConstruct %FirstStruct_0 [[v0]] [[v1]] [[v2]]
+// CHECK-NEXT: [[rwBuf_ptr:%\d+]] = OpAccessChain %_ptr_Uniform_FirstStruct %rwBuf %int_0 %uint_0
+// CHECK-NEXT:   [[anArray:%\d+]] = OpCompositeExtract %_arr_v3float_uint_4_0 [[values]] 0
+// CHECK-NEXT:  [[anArray1:%\d+]] = OpCompositeExtract %v3float [[anArray]] 0
+// CHECK-NEXT:  [[anArray2:%\d+]] = OpCompositeExtract %v3float [[anArray]] 1
+// CHECK-NEXT:  [[anArray3:%\d+]] = OpCompositeExtract %v3float [[anArray]] 2
+// CHECK-NEXT:  [[anArray4:%\d+]] = OpCompositeExtract %v3float [[anArray]] 3
+// CHECK-NEXT:      [[res1:%\d+]] = OpCompositeConstruct %_arr_v3float_uint_4 [[anArray1]] [[anArray2]] [[anArray3]] [[anArray4]]
+// CHECK-NEXT:      [[mats:%\d+]] = OpCompositeExtract %_arr_mat2v3float_uint_1_0 [[values]] 1
+// CHECK-NEXT:       [[mat:%\d+]] = OpCompositeExtract %mat2v3float [[mats]] 0
+// CHECK-NEXT:      [[res2:%\d+]] = OpCompositeConstruct %_arr_mat2v3float_uint_1 [[mat]]
+// CHECK-NEXT:      [[ints:%\d+]] = OpCompositeExtract %_arr_v2int_uint_3_0 [[values]] 2
+// CHECK-NEXT:     [[ints1:%\d+]] = OpCompositeExtract %v2int [[ints]] 0
+// CHECK-NEXT:     [[ints2:%\d+]] = OpCompositeExtract %v2int [[ints]] 1
+// CHECK-NEXT:     [[ints3:%\d+]] = OpCompositeExtract %v2int [[ints]] 2
+// CHECK-NEXT:      [[res3:%\d+]] = OpCompositeConstruct %_arr_v2int_uint_3 [[ints1]] [[ints2]] [[ints3]]
+// CHECK-NEXT:    [[result:%\d+]] = OpCompositeConstruct %FirstStruct [[res1]] [[res2]] [[res3]]
+// CHECK-NEXT:                      OpStore [[rwBuf_ptr]] [[result]]
+  rwBuf[0] = values;
+}