Use VPDom

Author: Mel-Chen

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -19,6 +19,7 @@
 #include "VPlan.h"
 #include "LoopVectorizationPlanner.h"
 #include "VPlanCFG.h"
+#include "VPlanDominatorTree.h"
 #include "VPlanPatternMatch.h"
 #include "VPlanTransforms.h"
 #include "VPlanUtils.h"
@@ -262,7 +263,12 @@ Value *VPTransformState::get(VPValue *Def, bool NeedsScalar) {
     return Data.VPV2Vector[Def];
 
   auto GetBroadcastInstrs = [this, Def](Value *V) {
-    bool SafeToHoist = !Def->hasDefiningRecipe();
+    VPDominatorTree VPDT(*Plan);
+    bool SafeToHoist =
+        !Def->hasDefiningRecipe() ||
+        VPDT.properlyDominates(Def->getDefiningRecipe()->getParent(),
+                               Plan->getVectorPreheader());
+
     if (VF.isScalar())
       return V;
     // Place the code for broadcasting invariant variables in the new preheader.

llvm/lib/Transforms/Vectorize/VPlanDominatorTree.h

@@ -39,8 +39,10 @@ class VPDominatorTree : public DominatorTreeBase<VPBlockBase, false> {
 
 public:
   VPDominatorTree() = default;
+  explicit VPDominatorTree(VPlan &Plan) { recalculate(Plan); }
 
   /// Returns true if \p A properly dominates \p B.
+  using Base::properlyDominates;
   bool properlyDominates(const VPRecipeBase *A, const VPRecipeBase *B);
 };