[llvm] [VPlan] Construct immutable VPIRBBs for exit blocks at construction(NFC) (PR #128374)

[via llvm-commits]

================
@@ -984,6 +989,12 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
   }
 }
 
+VPIRBasicBlock *VPlan::getExitBlock(BasicBlock *IRBB) const {
+  return *find_if(getExitBlocks(), [IRBB](const VPIRBasicBlock *VPIRBB) {
+    return VPIRBB->getIRBasicBlock() == IRBB;
+  });
----------------
ayalz wrote:

Better to hold the (one or two) exit blocks in a map keyed by their IRBB, than by a SmallVector?

https://github.com/llvm/llvm-project/pull/128374