[VPBuilder] Add setInsertPoint version taking a recipe directly (NFC).

This helps to slightly simplify code when a recipe can be obtained
easily. Suggested in D158779.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -120,6 +120,13 @@ class VPBuilder {
     InsertPt = IP;
   }
 
+  /// This specifies that created instructions should be inserted at the
+  /// specified point.
+  void setInsertPoint(VPRecipeBase *IP) {
+    BB = IP->getParent();
+    InsertPt = IP->getIterator();
+  }
+
   /// Create an N-ary operation with \p Opcode, \p Operands and set \p Inst as
   /// its underlying Instruction.
   VPValue *createNaryOp(unsigned Opcode, ArrayRef<VPValue *> Operands,

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -9133,7 +9133,7 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       VPValue *CondOp = nullptr;
       if (CM.blockNeedsPredicationForAnyReason(BB)) {
         VPBuilder::InsertPointGuard Guard(Builder);
-        Builder.setInsertPoint(LinkVPBB, CurrentLink->getIterator());
+        Builder.setInsertPoint(CurrentLink);
         CondOp = RecipeBuilder.createBlockInMask(BB, *Plan);
       }
 
@@ -9153,7 +9153,7 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
   // and the live-out instruction of each reduction, at the beginning of the
   // dedicated latch block.
   if (CM.foldTailByMasking()) {
-    Builder.setInsertPoint(LatchVPBB, LatchVPBB->begin());
+    Builder.setInsertPoint(&*LatchVPBB->begin());
     for (VPRecipeBase &R :
          Plan->getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
       VPReductionPHIRecipe *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);