[VPlan] Add VPSingleDefRecipe::dump() to resolve ambigous lookup (NFC).

This allows calling ::dump() on various sub-classes of VPSingleDefRecipe
directly, as it resolves an ambigous name lookup.

Previously, calling VPWidenRecipe::dump() (and others), would result in

the following errors:
llvm/unittests/Transforms/Vectorize/VPlanTest.cpp:1284:19: error: member 'dump' found in multiple base classes of different types
 1284 |           WidenR->dump();
      |                   ^
llvm/include/../lib/Transforms/Vectorize/VPlanValue.h:434:8: note: member found by ambiguous name lookup
  434 |   void dump() const;
      |        ^
llvm/include/../lib/Transforms/Vectorize/VPlanValue.h:108:8: note: member found by ambiguous name lookup
  108 |   void dump() const;
      |        ^
1 error generated.

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -954,6 +954,11 @@ public:
   /// Return the cost of this VPSingleDefRecipe.
   InstructionCost computeCost(ElementCount VF,
                               VPCostContext &Ctx) const override;
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  /// Print this VPSingleDefRecipe to dbgs() (for debugging).
+  LLVM_DUMP_METHOD void dump() const;
+#endif
 };
 
 /// Class to record LLVM IR flag for a recipe along with it.

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -343,6 +343,10 @@ FastMathFlags VPRecipeWithIRFlags::getFastMathFlags() const {
   return Res;
 }
 
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+void VPSingleDefRecipe::dump() const { VPDef::dump(); }
+#endif
+
 template <unsigned PartOpIdx>
 VPValue *
 VPUnrollPartAccessor<PartOpIdx>::getUnrollPartOperand(VPUser &U) const {

llvm/unittests/Transforms/Vectorize/VPlanTest.cpp

@@ -1279,6 +1279,21 @@ TEST(VPRecipeTest, dumpRecipeInPlan) {
         },
         testing::ExitedWithCode(0), "WIDEN ir<%a> = add ir<1>, ir<2>");
 
+    VPDef *Def = WidenR;
+    EXPECT_EXIT(
+        {
+          Def->dump();
+          exit(0);
+        },
+        testing::ExitedWithCode(0), "WIDEN ir<%a> = add ir<1>, ir<2>");
+
+    EXPECT_EXIT(
+        {
+          WidenR->dump();
+          exit(0);
+        },
+        testing::ExitedWithCode(0), "WIDEN ir<%a> = add ir<1>, ir<2>");
+
     // Test VPRecipeBase::dump().
     VPRecipeBase *R = WidenR;
     EXPECT_EXIT(