[LLVM-C] Allow For Creating a BasicBlock without a Parent Function

[CodaFi]

Summary

Add a utility function for creating a basic block without a parent function. A useful operation for compilers that need to synthesize and conditionally insert code without having to bother with appending and immediately unlinking a block.

[whitequark]

LGTM

include/llvm-c/Core.h

  * Obtain the basic block that corresponds to the entry point of a
  * function.
  *
  * @see llvm::Function::getEntryBlock()
  */
 LLVMBasicBlockRef LLVMGetEntryBasicBlock(LLVMValueRef Fn);
 
 /**
+ * Create a new basic block without inserting it into a function.
+ *
+ * @see llvm::BasicBlock::Create()
+ */
+LLVMBasicBlockRef LLVMCreateBasicBlockInContext(LLVMContextRef C,
+                                                const char *Name,
+                                                unsigned NameLen);
+
+/**
  * Append a basic block to the end of a function.
  *
  * @see llvm::BasicBlock::Create()
  */
 LLVMBasicBlockRef LLVMAppendBasicBlockInContext(LLVMContextRef C,
                                                 LLVMValueRef Fn,
                                                 const char *Name);
 

lib/IR/Core.cpp

 LLVMBasicBlockRef LLVMGetPreviousBasicBlock(LLVMBasicBlockRef BB) {
   BasicBlock *Block = unwrap(BB);
   Function::iterator I(Block);
   if (I == Block->getParent()->begin())
     return nullptr;
   return wrap(&*--I);
 }
 
+LLVMBasicBlockRef LLVMCreateBasicBlockInContext(LLVMContextRef C,
+                                                const char *Name,
+                                                unsigned NameLen) {
+  return wrap(llvm::BasicBlock::Create(*unwrap(C), StringRef(Name, NameLen)));
+}
+
 LLVMBasicBlockRef LLVMAppendBasicBlockInContext(LLVMContextRef C,
                                                 LLVMValueRef FnRef,
                                                 const char *Name) {
   return wrap(BasicBlock::Create(*unwrap(C), Name, unwrap<Function>(FnRef)));
 }
 
 LLVMBasicBlockRef LLVMAppendBasicBlock(LLVMValueRef FnRef, const char *Name) {
   return LLVMAppendBasicBlockInContext(LLVMGetGlobalContext(), FnRef, Name);