[llvm] [VPlan] Introduces explicit broadcast for live-in constants. (PR #133213)

[David Sherwood via llvm-commits]

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@@ -3093,8 +3090,25 @@ void VPlanTransforms::materializeBroadcasts(VPlan &Plan) {
                "All users must be in the vector preheader or dominated by it");
     }
 
-    VPBuilder Builder(cast<VPBasicBlock>(HoistBlock), HoistPoint);
-    auto *Broadcast = Builder.createNaryOp(VPInstruction::Broadcast, {VPV});
+    VPInstruction *Broadcast;
+    if (VPV->isLiveIn() && isa_and_nonnull<Constant>(VPV->getLiveInIRValue())) {
+      // We cannot replace the constant live-ins for PHIs by broadcast in the
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david-arm wrote:

I'm not sure I understand the relevance of PHIs in this code, since nothing else in this function seems to use or create them?

https://github.com/llvm/llvm-project/pull/133213