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

[via llvm-commits]

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@@ -9370,16 +9400,30 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
         // after them)
         // * Optimizing truncates to VPWidenIntOrFpInductionRecipe.
 
-        assert((HeaderVPBB->getFirstNonPhi() == VPBB->end() ||
-                CM.foldTailByMasking() || isa<TruncInst>(Instr)) &&
-               "unexpected recipe needs moving");
         Recipe->insertBefore(*HeaderVPBB, HeaderVPBB->getFirstNonPhi());
       } else
-        VPBB->appendRecipe(Recipe);
+        Recipe->insertBefore(&R);
+      if (Recipe->getNumDefinedValues() == 1)
+        SingleDef->replaceAllUsesWith(Recipe->getVPSingleValue());
+      else
+        assert(Recipe->getNumDefinedValues() == 0);
+      R.eraseFromParent();
     }
 
-    VPBlockUtils::insertBlockAfter(Plan->createVPBasicBlock(""), VPBB);
-    VPBB = cast<VPBasicBlock>(VPBB->getSingleSuccessor());
+    // 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
+    // predecessors and successors, except the exiting block. Then connect VPBB
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ayalz wrote:

What's special about the exiting block, want to retain edges that leave the loop to exit blocks?

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