[LoopVersioning] Add utility to fetch the runtime check basic block

[eopXD]

Summary

This allow user to get the basic block, get the BranchInst from BB.
The utility is needed when other passes that versions the loops want to
append more conditions to the runtime check.

[eopXD]

Update the code.

[eopXD]

This comment was removed by eopXD.

[Whitney]

This change looks like part of the change in https://reviews.llvm.org/D104631?

[eopXD]

In D104620#2962982, @Whitney wrote:

This change looks like part of the change in https://reviews.llvm.org/D104631?

Yes. I originally thought of splitting the modifications into two patches to make commits more obvious. Now I think a single patch would be good.
Aborting this patch and heading to D104631 to finish it.

llvm/include/llvm/Transforms/Utils/LoopVersioning.h

 //===- LoopVersioning.h - Utility to version a loop -------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
public:
   /// loop don't alias (i.e. all memchecks passed).  (This loop is actually the
   /// same as the original loop that we got constructed with.)
   Loop *getVersionedLoop() { return VersionedLoop; }
 
   /// Returns the fall-back loop.  Control flows here if pointers in the
   /// loop may alias (i.e. one of the memchecks failed).
   Loop *getNonVersionedLoop() { return NonVersionedLoop; }
 
+  /// Returns the basic block that contains the runtime check BranchInst
+  BasicBlock *getRuntimeCheckBB() { return RuntimeCheckBB; }
+
   /// Annotate memory instructions in the versioned loop with no-alias
   /// metadata based on the memchecks issued.
   ///
   /// This is just wrapper that calls prepareNoAliasMetadata and
   /// annotateInstWithNoAlias on the instructions of the versioned loop.
   void annotateLoopWithNoAlias();
 
   /// Set up the aliasing scopes based on the memchecks.  This needs to
private:
 
   /// The original loop.  This becomes the "versioned" one.  I.e.,
   /// control flows here if pointers in the loop don't alias.
   Loop *VersionedLoop;
   /// The fall-back loop.  I.e. control flows here if pointers in the
   /// loop may alias (memchecks failed).
   Loop *NonVersionedLoop;
 
+  /// The basic Block that stores the BranchInst to Versioned / NonVersioned
+  BasicBlock *RuntimeCheckBB;
+
   /// This maps the instructions from VersionedLoop to their counterpart
   /// in NonVersionedLoop.
   ValueToValueMapTy VMap;
 
   /// The set of alias checks that we are versioning for.
   SmallVector<RuntimePointerCheck, 4> AliasChecks;
 
   /// The set of SCEV checks that we are versioning for.

llvm/lib/Transforms/Utils/LoopVersioning.cpp

 //===- LoopVersioning.cpp - Utility to version a loop ---------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
assert(VersionedLoop->isLoopSimplifyForm() &&
          "Loop is not in loop-simplify form");
 
   Instruction *FirstCheckInst;
   Instruction *MemRuntimeCheck;
   Value *SCEVRuntimeCheck;
   Value *RuntimeCheck = nullptr;
 
   // Add the memcheck in the original preheader (this is empty initially).
-  BasicBlock *RuntimeCheckBB = VersionedLoop->getLoopPreheader();
+  RuntimeCheckBB = VersionedLoop->getLoopPreheader();
   const auto &RtPtrChecking = *LAI.getRuntimePointerChecking();
 
   SCEVExpander Exp2(*RtPtrChecking.getSE(),
                     VersionedLoop->getHeader()->getModule()->getDataLayout(),
                     "induction");
   std::tie(FirstCheckInst, MemRuntimeCheck) = addRuntimeChecks(
       RuntimeCheckBB->getTerminator(), VersionedLoop, AliasChecks, Exp2);