[move-only] Remove use after move in CopiedLoadBorrowEliminationVisitor.

Specifically, we were calling process on a visitor that was already moved. To
fix this I created a separate state structure that the visitor initializes and
moved the post-processing step onto the state data structure.

This seems to not be causing any problems today, but could in the future.

rdar://111060475

Author: gottesmm

lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp

@@ -1433,15 +1433,49 @@ class ExtendUnconsumedLiveness {
 
 namespace {
 
+struct CopiedLoadBorrowEliminationState {
+  SILFunction *fn;
+  StackList<LoadBorrowInst *> targets;
+
+  CopiedLoadBorrowEliminationState(SILFunction *fn) : fn(fn), targets(fn) {}
+
+  void process() {
+    if (targets.empty())
+      return;
+
+    while (!targets.empty()) {
+      auto *lbi = targets.pop_back_val();
+      SILBuilderWithScope builder(lbi);
+      SILValue li = builder.emitLoadValueOperation(
+          lbi->getLoc(), lbi->getOperand(), LoadOwnershipQualifier::Copy);
+      SILValue borrow = builder.createBeginBorrow(lbi->getLoc(), li);
+
+      for (auto *ebi : lbi->getEndBorrows()) {
+        auto *next = ebi->getNextInstruction();
+        SILBuilderWithScope builder(next);
+        auto loc = RegularLocation::getAutoGeneratedLocation();
+        builder.emitDestroyValueOperation(loc, li);
+      }
+
+      lbi->replaceAllUsesWith(borrow);
+      lbi->eraseFromParent();
+    }
+
+    LLVM_DEBUG(llvm::dbgs() << "After Load Borrow Elim. Func Dump Start! ";
+               fn->print(llvm::dbgs()));
+    LLVM_DEBUG(llvm::dbgs() << "After Load Borrow Elim. Func Dump End!\n");
+  }
+};
+
 /// An early transform that we run to convert any load_borrow that are copied
 /// directly or that have any subelement that is copied to a load [copy]. This
 /// lets the rest of the optimization handle these as appropriate.
 struct CopiedLoadBorrowEliminationVisitor final
     : public TransitiveAddressWalker {
-  SILFunction *fn;
-  StackList<LoadBorrowInst *> targets;
+  CopiedLoadBorrowEliminationState &state;
 
-  CopiedLoadBorrowEliminationVisitor(SILFunction *fn) : fn(fn), targets(fn) {}
+  CopiedLoadBorrowEliminationVisitor(CopiedLoadBorrowEliminationState &state)
+      : state(state) {}
 
   bool visitUse(Operand *op) override {
     LLVM_DEBUG(llvm::dbgs() << "CopiedLBElim visiting ";
@@ -1527,36 +1561,9 @@ struct CopiedLoadBorrowEliminationVisitor final
     if (!shouldConvertToLoadCopy)
       return true;
 
-    targets.push_back(lbi);
+    state.targets.push_back(lbi);
     return true;
   }
-
-  void process() {
-    if (targets.empty())
-      return;
-
-    while (!targets.empty()) {
-      auto *lbi = targets.pop_back_val();
-      SILBuilderWithScope builder(lbi);
-      SILValue li = builder.emitLoadValueOperation(
-          lbi->getLoc(), lbi->getOperand(), LoadOwnershipQualifier::Copy);
-      SILValue borrow = builder.createBeginBorrow(lbi->getLoc(), li);
-
-      for (auto *ebi : lbi->getEndBorrows()) {
-        auto *next = ebi->getNextInstruction();
-        SILBuilderWithScope builder(next);
-        auto loc = RegularLocation::getAutoGeneratedLocation();
-        builder.emitDestroyValueOperation(loc, li);
-      }
-
-      lbi->replaceAllUsesWith(borrow);
-      lbi->eraseFromParent();
-    }
-
-    LLVM_DEBUG(llvm::dbgs() << "After Load Borrow Elim. Func Dump Start! ";
-               fn->print(llvm::dbgs()));
-    LLVM_DEBUG(llvm::dbgs() << "After Load Borrow Elim. Func Dump End!\n");
-  }
 };
 
 } // namespace
@@ -3130,14 +3137,15 @@ bool MoveOnlyAddressCheckerPImpl::performSingleCheck(
   // [copy] + begin_borrow for further processing. This just eliminates a case
   // that the checker doesn't need to know about.
   {
-    CopiedLoadBorrowEliminationVisitor copiedLoadBorrowEliminator(fn);
+    CopiedLoadBorrowEliminationState state(markedAddress->getFunction());
+    CopiedLoadBorrowEliminationVisitor copiedLoadBorrowEliminator(state);
     if (AddressUseKind::Unknown ==
         std::move(copiedLoadBorrowEliminator).walk(markedAddress)) {
       LLVM_DEBUG(llvm::dbgs() << "Failed copied load borrow eliminator visit: "
                               << *markedAddress);
       return false;
     }
-    copiedLoadBorrowEliminator.process();
+    state.process();
   }
 
   // Then gather all uses of our address by walking from def->uses. We use this