[VPlan] Do not print mapping for Value2VPValue.

[fhahn]

Summary

The latest improvements to VPValue printing make this mapping clear when
printing the operand. Printing the mapping separately is not required
any longer.

[Ayal]

Minor nit.
Thanks for following up quickly on https://reviews.llvm.org/D76200#inline-694794

llvm/lib/Transforms/Vectorize/VPlan.cpp

585

This second if is now redundant.

Once we can assign VPValues (meaningful) names, this should be removed as well.

[fhahn]

Thanks Ayal! I've committed the change with the redundant if removed.

llvm/lib/Transforms/Vectorize/VPlan.cpp

 
 void VPlanPrinter::dump() {
   Depth = 1;
   bumpIndent(0);
   OS << "digraph VPlan {\n";
   OS << "graph [labelloc=t, fontsize=30; label=\"Vectorization Plan";
   if (!Plan.getName().empty())
     OS << "\\n" << DOT::EscapeString(Plan.getName());
-  if (!Plan.Value2VPValue.empty() || Plan.BackedgeTakenCount) {
+  if (Plan.BackedgeTakenCount) {
     OS << ", where:";
     if (Plan.BackedgeTakenCount) {
       OS << "\\n";
       Plan.BackedgeTakenCount->print(OS, SlotTracker);
       OS << " := BackedgeTakenCount";
     }
-    for (auto Entry : Plan.Value2VPValue) {
-      OS << "\\n";
-      Entry.second->print(OS, SlotTracker);
-      OS << DOT::EscapeString(" := ");
-      Entry.first->printAsOperand(OS, false);
-    }
   }
   OS << "\"]\n";
   OS << "node [shape=rect, fontname=Courier, fontsize=30]\n";
   OS << "edge [fontname=Courier, fontsize=30]\n";
   OS << "compound=true\n";
 
   for (const VPBlockBase *Block : depth_first(Plan.getEntry()))
     dumpBlock(Block);

llvm/unittests/Transforms/Vectorize/VPlanHCFGTest.cpp

TEST_F(VPlanHCFGTest, testBuildHCFGInnerLoop) {
   EXPECT_EQ(Phi, IndvarAdd->getOperand(0));
 
   VPInstruction *ICmp = dyn_cast<VPInstruction>(&*Iter++);
   EXPECT_EQ(Instruction::ICmp, ICmp->getOpcode());
   EXPECT_EQ(2u, ICmp->getNumOperands());
   EXPECT_EQ(IndvarAdd, ICmp->getOperand(0));
   EXPECT_EQ(VecBB->getCondBit(), ICmp);
 
+  // Add an external value to check we do not print the list of external values,
+  // as this is not required with the new printing.
+  Plan->addVPValue(&*F->arg_begin());
   std::string FullDump;
   raw_string_ostream(FullDump) << *Plan;
   EXPECT_EQ(R"(digraph VPlan {
 graph [labelloc=t, fontsize=30; label="Vectorization Plan"]
 node [shape=rect, fontname=Courier, fontsize=30]
 edge [fontname=Courier, fontsize=30]
 compound=true
   subgraph cluster_N0 {