[llvm] [VPlan] Build initial VPlan 0 using HCFGBuilder for inner loops. (NFC) (PR #124432)

[via llvm-commits]

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@@ -9376,25 +9419,29 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
         Recipe = RecipeBuilder.handleReplication(Instr, Operands, Range);
 
       RecipeBuilder.setRecipe(Instr, Recipe);
-      if (isa<VPHeaderPHIRecipe>(Recipe)) {
-        // VPHeaderPHIRecipes must be kept in the phi section of HeaderVPBB. In
-        // the following cases, VPHeaderPHIRecipes may be created after non-phi
-        // recipes and need to be moved to the phi section of HeaderVPBB:
-        // * tail-folding (non-phi recipes computing the header mask are
-        // introduced earlier than regular header phi recipes, and should appear
-        // after them)
-        // * Optimizing truncates to VPWidenIntOrFpInductionRecipe.
-
-        assert((HeaderVPBB->getFirstNonPhi() == VPBB->end() ||
-                CM.foldTailByMasking() || isa<TruncInst>(Instr)) &&
-               "unexpected recipe needs moving");
+      if (isa<VPWidenIntOrFpInductionRecipe>(Recipe) && isa<TruncInst>(Instr)) {
+        // Optimized a truncate to VPWidenIntOrFpInductionRecipe. It needs to be
+        // moved to the phi section in the header.
         Recipe->insertBefore(*HeaderVPBB, HeaderVPBB->getFirstNonPhi());
-      } else
-        VPBB->appendRecipe(Recipe);
-    }
-
-    VPBlockUtils::insertBlockAfter(Plan->createVPBasicBlock(""), VPBB);
-    VPBB = cast<VPBasicBlock>(VPBB->getSingleSuccessor());
+      } else {
+        Builder.insert(Recipe);
+      }
+      if (Recipe->getNumDefinedValues() == 1)
+        SingleDef->replaceAllUsesWith(Recipe->getVPSingleValue());
+      else
+        assert(Recipe->getNumDefinedValues() == 0 &&
+               "Unexpected multidef recipe");
+      R.eraseFromParent();
+    }
+
+    // Flatten the CFG in the loop. Masks for blocks have already been generated
+    // and added to recipes as needed. To do so, first disconnect VPBB from its
+    // successors. Then connect VPBB to the previously visited$ VPBB.
----------------
ayalz wrote:

```suggestion
    // successors. Then connect VPBB to the previously visited VPBB.
```

https://github.com/llvm/llvm-project/pull/124432