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

[via llvm-commits]

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@@ -8902,29 +8913,26 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
   }
 }
 
-// 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 along with its loop branch, but w/o its
+// increment - which is introduced later.
+static void addCanonicalIV(VPlan &Plan, Type *IdxTy, DebugLoc DL) {
   Value *StartIdx = ConstantInt::get(IdxTy, 0);
   auto *StartV = Plan.getOrAddLiveIn(StartIdx);
 
   // Add a VPCanonicalIVPHIRecipe starting at 0 to the header.
+  // TODO: Introduce a separate scalar phi recipe that can be used for codegen,
+  // turning VPCanonicalIVPHIRecipe into an 'abstract' recipe which cannot be
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ayalz wrote:

VPCanonicalIVPHIRecipe, as a phi recipe in the header block, and BranchOnCount as a recipe in the latch, seem to retain their individual concrete semantics, even if the increment is introduced later between them.

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