[llvm] [VPlan] Return invalid cost if any skeleton block has invalid costs. (PR #151940)

[via llvm-commits]

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@@ -1054,12 +1054,17 @@ void VPlan::execute(VPTransformState *State) {
 
 InstructionCost VPlan::cost(ElementCount VF, VPCostContext &Ctx) {
   // For now only return the cost of the vector loop region, ignoring any other
-  // blocks, like the preheader or middle blocks.
+  // blocks, like the preheader or middle blocks, expect for checking them for
+  // recipes with invalid costs.
   InstructionCost Cost = getVectorLoopRegion()->cost(VF, Ctx);
 
-  // If any instructions in the middle block are invalid return invalid.
-  // TODO: Remove once no VPlans with VF == vscale x 1 and first-order recurrences are created.
-  if (!getMiddleBlock()->cost(VF, Ctx).isValid())
+  // If the cost of the loop region is invalid or any recipe in the skeleton
+  // outside loop regions are invalid return an invalid cost.
+  if (!Cost.isValid() || any_of(VPBlockUtils::blocksOnly<VPBasicBlock>(
+                                    vp_depth_first_shallow(getEntry())),
+                                [&VF, &Ctx](VPBasicBlock *VPBB) {
+                                  return !VPBB->cost(VF, Ctx).isValid();
+                                }))
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ayalz wrote:

Worth checking the any_of() part and potentially bailing out before computing the `Cost` of the vector loop?

https://github.com/llvm/llvm-project/pull/151940