[LoopUtils] Simplify addRuntimeCheck to return a single value.

This simplifies the return value of addRuntimeCheck from a pair of
instructions to a single `Value *`.

The existing users of addRuntimeChecks were ignoring the first element
of the pair, hence there is not reason to track FirstInst and return
it.

Additionally all users of addRuntimeChecks use the second returned
`Instruction *` just as `Value *`, so there is no need to return an
`Instruction *`. Therefore there is no need to create a redundant
dummy `and X, true` instruction any longer.

Effectively this change should not impact the generated code because the
redundant AND will be folded by later optimizations. But it is easy to
avoid creating it in the first place and it allows more accurately
estimating the cost of the runtime checks.

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopVersioning.cpp b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
index 3498f29..771b7d2 100644
--- a/llvm/lib/Transforms/Utils/LoopVersioning.cpp
+++ b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
@@ -52,8 +52,7 @@ void LoopVersioning::versionLoop(
   assert(VersionedLoop->isLoopSimplifyForm() &&
          "Loop is not in loop-simplify form");
 
-  Instruction *FirstCheckInst;
-  Instruction *MemRuntimeCheck;
+  Value *MemRuntimeCheck;
   Value *SCEVRuntimeCheck;
   Value *RuntimeCheck = nullptr;
 
@@ -64,8 +63,8 @@ void LoopVersioning::versionLoop(
   SCEVExpander Exp2(*RtPtrChecking.getSE(),
                     VersionedLoop->getHeader()->getModule()->getDataLayout(),
                     "induction");
-  std::tie(FirstCheckInst, MemRuntimeCheck) = addRuntimeChecks(
-      RuntimeCheckBB->getTerminator(), VersionedLoop, AliasChecks, Exp2);
+  MemRuntimeCheck = addRuntimeChecks(RuntimeCheckBB->getTerminator(),
+                                     VersionedLoop, AliasChecks, Exp2);
 
   SCEVExpander Exp(*SE, RuntimeCheckBB->getModule()->getDataLayout(),
                    "scev.check");