[NFC][LoopPredication] Add parsed checks logging

[aleksandr.popov]

This have been reviewed in the https://reviews.llvm.org/D157276 and was suggested to land without additional review

llvm/lib/Transforms/Scalar/LoopPredication.cpp

for (auto &Check : Checks)
     if (ICmpInst *ICI = dyn_cast<ICmpInst>(Check))
       if (auto NewRangeCheck = widenICmpRangeCheck(ICI, Expander, Guard)) {
         NumWidened++;
         Check = *NewRangeCheck;
       }
   return NumWidened;
 }
 
-bool LoopPredication::widenGuardConditions(IntrinsicInst *Guard,
-                                           SCEVExpander &Expander) {
+static SmallVector<Value *> extractChecksFromGuard(Instruction *Guard) {
   LLVM_DEBUG(dbgs() << "Processing guard:\n");
   LLVM_DEBUG(Guard->dump());
 
-  TotalConsidered++;
   SmallVector<Value *, 4> Checks;
   parseWidenableGuard(Guard, Checks);
+  LLVM_DEBUG(dbgs() << "Found checks:\n");
+  std::for_each(Checks.begin(), Checks.end(), [](const Value *Check) {
+    LLVM_DEBUG(dbgs() << *Check << "\n");
+  });
+  return Checks;
+}
+
+bool LoopPredication::widenGuardConditions(IntrinsicInst *Guard,
+                                           SCEVExpander &Expander) {
+  TotalConsidered++;
+  auto Checks = extractChecksFromGuard(Guard);
   unsigned NumWidened = widenChecks(Checks, Expander, Guard);
   if (NumWidened == 0)
     return false;
 
   TotalWidened += NumWidened;
 
   // Emit the new guard condition
   IRBuilder<> Builder(findInsertPt(Guard, Checks));
   Value *AllChecks = Builder.CreateAnd(Checks);
   auto *OldCond = Guard->getOperand(0);
   Guard->setOperand(0, AllChecks);
   if (InsertAssumesOfPredicatedGuardsConditions) {
     Builder.SetInsertPoint(&*++BasicBlock::iterator(Guard));
     Builder.CreateAssumption(OldCond);
   }
   RecursivelyDeleteTriviallyDeadInstructions(OldCond, nullptr /* TLI */, MSSAU);
 
   LLVM_DEBUG(dbgs() << "Widened checks = " << NumWidened << "\n");
   return true;
 }
 
 bool LoopPredication::widenWidenableBranchGuardConditions(
     BranchInst *BI, SCEVExpander &Expander) {
   assert(isGuardAsWidenableBranch(BI) && "Must be!");
-  LLVM_DEBUG(dbgs() << "Processing guard:\n");
-  LLVM_DEBUG(BI->dump());
 
   Value *Cond, *WC;
   BasicBlock *IfTrueBB, *IfFalseBB;
   bool Parsed = parseWidenableBranch(BI, Cond, WC, IfTrueBB, IfFalseBB);
   assert(Parsed && "Must be able to parse widenable branch");
   (void)Parsed;
 
   TotalConsidered++;
-  SmallVector<Value *, 4> Checks;
-  parseWidenableGuard(BI, Checks);
+  auto Checks = extractChecksFromGuard(BI);
   // At the moment, our matching logic for wideable conditions implicitly
   // assumes we preserve the form: (br (and Cond, WC())).  FIXME
   Checks.push_back(WC);
   unsigned NumWidened = widenChecks(Checks, Expander, BI);
   if (NumWidened == 0)
     return false;
 
   TotalWidened += NumWidened;

llvm/test/Transforms/LoopPredication/visited.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -passes=loop-predication < %s 2>&1 | FileCheck %s
-; RUN: opt -S -passes='require<scalar-evolution>,loop-mssa(loop-predication)' -verify-memoryssa < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes=loop-predication -debug-only=loop-predication < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='require<scalar-evolution>,loop-mssa(loop-predication)' -verify-memoryssa -debug-only=loop-predication < %s 2>&1 | FileCheck %s
+; REQUIRES: asserts
 
 declare void @llvm.experimental.guard(i1, ...)
 
 define i32 @test_visited(ptr %array, i32 %length, i32 %n, i32 %x) {
+; CHECK: Found checks:
+; CHECK-NEXT: %unrelated.cond = icmp eq i32 %x, %i
+; CHECK-NEXT: %within.bounds = icmp ult i32 %i, %length
+;
 ; CHECK-LABEL: @test_visited(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP5:%.*]] = icmp eq i32 [[N:%.*]], 0
 ; CHECK-NEXT:    br i1 [[TMP5]], label [[EXIT:%.*]], label [[LOOP_PREHEADER:%.*]]
 ; CHECK:       loop.preheader:
 ; CHECK-NEXT:    [[TMP0:%.*]] = icmp ule i32 [[N]], [[LENGTH:%.*]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i32 0, [[LENGTH]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = and i1 [[TMP1]], [[TMP0]]