[IR] Adds Function::erase() for erasing a range of basic blocks

[vporpo]

Summary

This is part of a series of patches that aim at making Function::getBasicBlockList() private.

llvm/include/llvm/IR/Function.h

public:
   }
 
   /// Transfer a range of basic blocks that belong to \p FromF from \p
   /// FromBeginIt to \p FromEndIt, to this function at \p ToIt.
   void splice(Function::iterator ToIt, Function *FromF,
               Function::iterator FromBeginIt,
               Function::iterator FromEndIt);
 
+  /// Erases a range of BasicBlocks from \p FromIt to (not including) \p ToIt.
+  /// \Returns \p ToIt.
+  Function::iterator erase(Function::iterator FromIt, Function::iterator ToIt);
+
   /// Get the underlying elements of the Function... the basic block list is
   /// empty for external functions.
   ///
   const BasicBlockListType &getBasicBlockList() const { return BasicBlocks; }
         BasicBlockListType &getBasicBlockList()       { return BasicBlocks; }
 
   static BasicBlockListType Function::*getSublistAccess(BasicBlock*) {
     return &Function::BasicBlocks;

llvm/lib/IR/Function.cpp

#ifdef EXPENSIVE_CHECKS
   // Check that FromBeginIt is before FromEndIt.
   auto FromFEnd = FromF->end();
   for (auto It = FromBeginIt; It != FromEndIt; ++It)
     assert(It != FromFEnd && "FromBeginIt not before FromEndIt!");
 #endif // EXPENSIVE_CHECKS
   BasicBlocks.splice(ToIt, FromF->BasicBlocks, FromBeginIt, FromEndIt);
 }
 
+Function::iterator Function::erase(Function::iterator FromIt,
+                                   Function::iterator ToIt) {
+  return BasicBlocks.erase(FromIt, ToIt);
+}
+
 //===----------------------------------------------------------------------===//
 // Function Implementation
 //===----------------------------------------------------------------------===//
 
 static unsigned computeAddrSpace(unsigned AddrSpace, Module *M) {
   // If AS == -1 and we are passed a valid module pointer we place the function
   // in the program address space. Otherwise we default to AS0.
   if (AddrSpace == static_cast<unsigned>(-1))

llvm/unittests/IR/FunctionTest.cpp

)");
   Function *ToF = M->getFunction("to");
   BasicBlock *ToBB2 = getBBWithName(ToF, "to_bb2");
 
   EXPECT_DEATH(ToF->splice(ToBB2->getIterator(), FromF, FromBB2->getIterator(),
                            FromBB1->getIterator()),
                "FromBeginIt not before FromEndIt!");
 }
 #endif //EXPENSIVE_CHECKS
+
+TEST(FunctionTest, EraseBBs) {
+  LLVMContext Ctx;
+  std::unique_ptr<Module> M = parseIR(Ctx, R"(
+    define void @foo() {
+     bb1:
+       br label %bb2
+     bb2:
+       br label %bb3
+     bb3:
+       br label %bb4
+     bb4:
+       br label %bb5
+     bb5:
+       ret void
+    }
+)");
+
+  Function *F = M->getFunction("foo");
+  BasicBlock *BB1 = getBBWithName(F, "bb1");
+  BasicBlock *BB2 = getBBWithName(F, "bb2");
+  BasicBlock *BB3 = getBBWithName(F, "bb3");
+  BasicBlock *BB4 = getBBWithName(F, "bb4");
+  BasicBlock *BB5 = getBBWithName(F, "bb5");
+  EXPECT_EQ(F->size(), 5u);
+
+  // Erase BB2.
+  BB1->getTerminator()->eraseFromParent();
+  auto It = F->erase(BB2->getIterator(), std::next(BB2->getIterator()));
+  EXPECT_EQ(F->size(), 4u);
+  // Check that the iterator returned matches the node after the erased one.
+  EXPECT_EQ(It, BB3->getIterator());
+
+  It = F->begin();
+  EXPECT_EQ(&*It++, BB1);
+  EXPECT_EQ(&*It++, BB3);
+  EXPECT_EQ(&*It++, BB4);
+  EXPECT_EQ(&*It++, BB5);
+
+  // Erase all BBs.
+  It = F->erase(F->begin(), F->end());
+  EXPECT_EQ(F->size(), 0u);
+}
 } // end namespace