[OCaml] Code simplification using string allocation functions

[jberdine]

Summary

Using the cstr_to_string function that allocates and initializes an
OCaml string value enables simplifications in several cases. This
change also has the effect of avoiding calling memcpy on NULL
pointers even if only 0 bytes are to be copied.

llvm/bindings/ocaml/llvm/llvm_ocaml.c

 CAMLprim value llvm_is_string_attr(LLVMAttributeRef A) {
   return Val_int(LLVMIsStringAttribute(A));
 }
 
 /* llattribute -> string */
 CAMLprim value llvm_get_string_attr_kind(LLVMAttributeRef A) {
   unsigned Length;
   const char *String = LLVMGetStringAttributeKind(A, &Length);
-  value Result = caml_alloc_string(Length);
-  memcpy((char *)String_val(Result), String, Length);
-  return Result;
+  return cstr_to_string (String, Length);
 }
 
 /* llattribute -> string */
 CAMLprim value llvm_get_string_attr_value(LLVMAttributeRef A) {
   unsigned Length;
   const char *String = LLVMGetStringAttributeValue(A, &Length);
-  value Result = caml_alloc_string(Length);
-  memcpy((char *)String_val(Result), String, Length);
-  return Result;
+  return cstr_to_string (String, Length);
 }
 
 /*===-- Modules -----------------------------------------------------------===*/
 
 /* llcontext -> string -> llmodule */
 CAMLprim LLVMModuleRef llvm_create_module(LLVMContextRef C, value ModuleID) {
   return LLVMModuleCreateWithNameInContext(String_val(ModuleID), C);
 }
CAMLprim LLVMMemoryBufferRef llvm_memorybuffer_of_string(value Name, value String) {
   MemBuf = LLVMCreateMemoryBufferWithMemoryRangeCopy(
                 String_val(String), caml_string_length(String), NameCStr);
 
   return MemBuf;
 }
 
 /* llmemorybuffer -> string */
 CAMLprim value llvm_memorybuffer_as_string(LLVMMemoryBufferRef MemBuf) {
-  value String = caml_alloc_string(LLVMGetBufferSize(MemBuf));
-  memcpy((char *)String_val(String), LLVMGetBufferStart(MemBuf),
-         LLVMGetBufferSize(MemBuf));
-
-  return String;
+  size_t BufferSize = LLVMGetBufferSize(MemBuf);
+  const char *BufferStart = LLVMGetBufferStart(MemBuf);
+  return cstr_to_string(BufferStart, BufferSize);
 }
 
 /* llmemorybuffer -> unit */
 CAMLprim value llvm_memorybuffer_dispose(LLVMMemoryBufferRef MemBuf) {
   LLVMDisposeMemoryBuffer(MemBuf);
   return Val_unit;
 }