[clang] [HLSL] Disable implicit constructors for user-defined structs/classes (PR #194989)

[Steven Perron via cfe-commits]

================
@@ -34,18 +36,14 @@ void main(unsigned GI : SV_GroupIndex) {
   Out2[GI] = In[GI];
 #endif
 
-  // For SPIR-V, the addrspacecast comes from `S::operator=` member function, which expects
-  // parameters in address space 0. This is why hlsl_device is a sub address
-  // space of the default address space.
-  // SPV: %[[INPTR:.*]] = call noundef align 1 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.VulkanBuffer_a0s_struct.Ss_12_1t.i32(target("spirv.VulkanBuffer", [0 x %struct.S], 12, 1) %{{.*}}, i32 %{{.*}})
-  // SPV: %[[INCAST:.*]] = addrspacecast ptr addrspace(11) %[[INPTR]] to ptr
   // SPV: %[[OUTPTR:.*]] = call noundef align 1 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.VulkanBuffer_a0s_struct.Ss_12_1t.i32(target("spirv.VulkanBuffer", [0 x %struct.S], 12, 1) %{{.*}}, i32 %{{.*}})
-  // SPV: %[[OUTCAST:.*]] = addrspacecast ptr addrspace(11) %[[OUTPTR]] to ptr
-  // SPV: call void @llvm.memcpy.p0.p0.i64(ptr align 1 %[[OUTCAST]], ptr align 1 %[[INCAST]], i64 4, i1 false)
+  // SPV: %[[INPTR:.*]] = call noundef align 1 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.VulkanBuffer_a0s_struct.Ss_12_1t.i32(target("spirv.VulkanBuffer", [0 x %struct.S], 12, 1) %{{.*}}, i32 %{{.*}})
+  // SPV: call void @llvm.memcpy.p11.p11.i64(ptr addrspace(11) align 1 %[[OUTPTR]], ptr addrspace(11) align 1 %[[INPTR]], i64 4, i1 false)
----------------
s-perron wrote:

In the past, `memcpy` has caused problems. Because the pointers are technically `void*` in memcpy, the llvm optimizer is free to create different code for it. It will sometimes replace it with loads and stores of i64 if the size is 64-bits. Then we end up with type mismatches in the generated spir-v.

If the `memcpy` stays as a memcpy, it will be turned into `OpCopyMemory`, which will work.

https://github.com/llvm/llvm-project/pull/194989