[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, 2 insertions, 28 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 7896d55..202c17d 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -1561,7 +1561,7 @@ expandBounds(const SmallVectorImpl<RuntimePointerCheck> &PointerChecks, Loop *L,
   return ChecksWithBounds;
 }
 
-std::pair<Instruction *, Instruction *> llvm::addRuntimeChecks(
+Value *llvm::addRuntimeChecks(
     Instruction *Loc, Loop *TheLoop,
     const SmallVectorImpl<RuntimePointerCheck> &PointerChecks,
     SCEVExpander &Exp) {
@@ -1570,22 +1570,10 @@ std::pair<Instruction *, Instruction *> llvm::addRuntimeChecks(
   auto ExpandedChecks = expandBounds(PointerChecks, TheLoop, Loc, Exp);
 
   LLVMContext &Ctx = Loc->getContext();
-  Instruction *FirstInst = nullptr;
   IRBuilder<> ChkBuilder(Loc);
   // Our instructions might fold to a constant.
   Value *MemoryRuntimeCheck = nullptr;
 
-  // FIXME: this helper is currently a duplicate of the one in
-  // LoopVectorize.cpp.
-  auto GetFirstInst = [](Instruction *FirstInst, Value *V,
-                         Instruction *Loc) -> Instruction * {
-    if (FirstInst)
-      return FirstInst;
-    if (Instruction *I = dyn_cast<Instruction>(V))
-      return I->getParent() == Loc->getParent() ? I : nullptr;
-    return nullptr;
-  };
-
   for (const auto &Check : ExpandedChecks) {
     const PointerBounds &A = Check.first, &B = Check.second;
     // Check if two pointers (A and B) conflict where conflict is computed as:
@@ -1614,30 +1602,16 @@ std::pair<Instruction *, Instruction *> llvm::addRuntimeChecks(
     // bound1 = (A.Start < B.End)
     //  IsConflict = bound0 & bound1
     Value *Cmp0 = ChkBuilder.CreateICmpULT(Start0, End1, "bound0");
-    FirstInst = GetFirstInst(FirstInst, Cmp0, Loc);
     Value *Cmp1 = ChkBuilder.CreateICmpULT(Start1, End0, "bound1");
-    FirstInst = GetFirstInst(FirstInst, Cmp1, Loc);
     Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict");
-    FirstInst = GetFirstInst(FirstInst, IsConflict, Loc);
     if (MemoryRuntimeCheck) {
       IsConflict =
           ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict, "conflict.rdx");
-      FirstInst = GetFirstInst(FirstInst, IsConflict, Loc);
     }
     MemoryRuntimeCheck = IsConflict;
   }
 
-  if (!MemoryRuntimeCheck)
-    return std::make_pair(nullptr, nullptr);
-
-  // We have to do this trickery because the IRBuilder might fold the check to a
-  // constant expression in which case there is no Instruction anchored in a
-  // the block.
-  Instruction *Check =
-      BinaryOperator::CreateAnd(MemoryRuntimeCheck, ConstantInt::getTrue(Ctx));
-  ChkBuilder.Insert(Check, "memcheck.conflict");
-  FirstInst = GetFirstInst(FirstInst, Check, Loc);
-  return std::make_pair(FirstInst, Check);
+  return MemoryRuntimeCheck;
 }
 
 Optional<IVConditionInfo> llvm::hasPartialIVCondition(Loop &L,