[llvm] [VPlan] Delay adding canonical IV increment and exit branches. (PR #82270)

[Florian Hahn via llvm-commits]

================
@@ -8491,17 +8499,16 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
         VPlanTransforms::truncateToMinimalBitwidths(
             *Plan, CM.getMinimalBitwidths(), PSE.getSE()->getContext());
       VPlanTransforms::optimize(*Plan, *PSE.getSE());
-      assert(verifyVPlanIsValid(*Plan) && "VPlan is invalid");
+      assert(verifyVPlanIsValid(*Plan, /*IsAbstract*/ true) &&
+             "VPlan is invalid");
       VPlans.push_back(std::move(Plan));
     }
     VF = SubRange.End;
   }
 }
 
-// Add the necessary canonical IV and branch recipes required to control the
-// loop.
-static void addCanonicalIVRecipes(VPlan &Plan, Type *IdxTy, bool HasNUW,
-                                  DebugLoc DL) {
+// Add the required canonical IV
+static void addCanonicalIV(VPlan &Plan, Type *IdxTy, bool HasNUW, DebugLoc DL) {
----------------
fhahn wrote:

I think eventually CanonicalIVPHI could become itself an 'abstract' recipe (terminology needs to determined), that doesn't codegen itself. Instead of adding the increment as operand in `prepareToExecute` we could replace it with a generic scalar PHI recipe, which could take care of codegen for any scalar phis (including EVL phi among others).

Could introduce a temporary recipe, but once we are converging on the overall approach, I can also put up a follow-up PR to use the generic scalar PHI recipe.

https://github.com/llvm/llvm-project/pull/82270