[llvm] [VPlan] Introduce recipes for VP loads and stores. (PR #87816)

[via llvm-commits]

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@@ -1203,43 +1203,48 @@ static VPActiveLaneMaskPHIRecipe *addVPLaneMaskPhiAndUpdateExitBranch(
   return LaneMaskPhi;
 }
 
-/// Replaces (ICMP_ULE, WideCanonicalIV, backedge-taken-count) pattern using
-/// the given \p Idiom.
-static void
-replaceHeaderPredicateWith(VPlan &Plan, VPValue &Idiom,
-                           function_ref<bool(VPUser &, unsigned)> Cond = {}) {
+/// Apply \p Fn to all VPInstructions matching the header mask (ICMP_ULE,
+/// WideCanonicalIV, backedge-taken-count) pattern
+static void forAllHeaderPredicates(VPlan &Plan,
+                                   function_ref<void(VPInstruction &)> Fn) {
+  SmallVector<VPValue *> WideCanonicalIVs;
   auto *FoundWidenCanonicalIVUser =
       find_if(Plan.getCanonicalIV()->users(),
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ayalz wrote:

Only a at-most one WidenCanonicalIVRecipe user expected (worth asserting?), or simply iterate over all users possibly pushing multiple candidates into the worklist, as with widen int or fp induction recipes below?

Instead of a pattern matching search for header masks, introduce an abstract HeaderMask recipe, which is later (i.e., here) lowered into an ICMP_ULE, ActiveLaneMask, EVL, whatnot?

https://github.com/llvm/llvm-project/pull/87816