[VPlan] Add VPlan::getTrue/getFalse convenience helpers (NFC).

Makes it slightly more convenient to create true/false constants.
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index 39f5e36..c13fe45 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -4132,6 +4132,18 @@
     return It->second;
   }
 
+  /// Return a VPValue wrapping i1 true.
+  VPValue *getTrue() {
+    LLVMContext &Ctx = getContext();
+    return getOrAddLiveIn(ConstantInt::getTrue(Ctx));
+  }
+
+  /// Return a VPValue wrapping i1 false.
+  VPValue *getFalse() {
+    LLVMContext &Ctx = getContext();
+    return getOrAddLiveIn(ConstantInt::getFalse(Ctx));
+  }
+
   /// Return the live-in VPValue for \p V, if there is one or nullptr otherwise.
   VPValue *getLiveIn(Value *V) const { return Value2VPValue.lookup(V); }
 
diff --git a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
index a66c4a7..1b91901 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
@@ -570,8 +570,7 @@
   VPBuilder Builder(MiddleVPBB);
   VPValue *Cmp;
   if (!RequiresScalarEpilogueCheck)
-    Cmp = Plan.getOrAddLiveIn(
-        ConstantInt::getFalse(IntegerType::getInt1Ty(Plan.getContext())));
+    Cmp = Plan.getFalse();
   else if (TailFolded)
     Cmp = Plan.getOrAddLiveIn(
         ConstantInt::getTrue(IntegerType::getInt1Ty(Plan.getContext())));
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 3ecffc7..99b6914 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1502,10 +1502,8 @@
   } else {
     // The vector region contains header phis for which we cannot remove the
     // loop region yet.
-    LLVMContext &Ctx = SE.getContext();
-    auto *BOC = new VPInstruction(
-        VPInstruction::BranchOnCond,
-        {Plan.getOrAddLiveIn(ConstantInt::getTrue(Ctx))}, Term->getDebugLoc());
+    auto *BOC = new VPInstruction(VPInstruction::BranchOnCond, {Plan.getTrue()},
+                                  Term->getDebugLoc());
     ExitingVPBB->appendRecipe(BOC);
   }
 
@@ -2171,7 +2169,7 @@
   Type *CanonicalIVType = Plan.getCanonicalIV()->getScalarType();
   VPTypeAnalysis TypeInfo(CanonicalIVType);
   LLVMContext &Ctx = CanonicalIVType->getContext();
-  VPValue *AllOneMask = Plan.getOrAddLiveIn(ConstantInt::getTrue(Ctx));
+  VPValue *AllOneMask = Plan.getTrue();
   VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
   VPBasicBlock *Header = LoopRegion->getEntryBasicBlock();