[move-function] Convert an assert into an early exit.

This assert was making sure we never saw a reborrow since they shouldn't occur
in Raw SIL. Some people were reporting that they /are/ hitting this assert, so I
am converting it into an early exit + skip analyzing an address. This will
prevent the assertion and also will fulfill the same purpose as the original,
not performing the move checking.

This will still result in correctness since if we skip as a move marker
instruction as a result of us skipping processing an address, the pass will emit
a compile time diagnostic saying the checker wasn't able to understand the given
code. So not the best, but at least if this hits a move itself we will be ok.

(cherry picked from commit eb03fb6)

Author: gottesmm

lib/SILOptimizer/Mandatory/MoveKillsCopyableValuesChecker.cpp

@@ -80,8 +80,6 @@ struct CheckerLivenessInfo {
 } // end anonymous namespace
 
 bool CheckerLivenessInfo::compute() {
-  bool foundEscapes = false;
-
   LLVM_DEBUG(llvm::dbgs() << "LivenessVisitor Begin!\n");
   while (SILValue value = defUseWorklist.pop()) {
     LLVM_DEBUG(llvm::dbgs() << "New Value: " << value);
@@ -108,7 +106,8 @@ bool CheckerLivenessInfo::compute() {
       // escape. Is it legal to canonicalize ForwardingUnowned?
       case OperandOwnership::ForwardingUnowned:
       case OperandOwnership::PointerEscape:
-        foundEscapes = true;
+        // This is an escape but it is up to the user to handle this, move
+        // checking stops here.
         break;
       case OperandOwnership::InstantaneousUse:
       case OperandOwnership::UnownedInstantaneousUse:
@@ -133,8 +132,8 @@ bool CheckerLivenessInfo::compute() {
           // binding that should be tracked separately.
           if (!bbi->isLexical()) {
             bool failed = !liveness.updateForBorrowingOperand(use);
-            assert(!failed &&
-                   "Shouldn't see reborrows this early in the pipeline");
+            if (failed)
+              return false;
           }
         }
         break;
@@ -178,8 +177,8 @@ bool CheckerLivenessInfo::compute() {
     }
   }
 
-  // We succeeded if we did not find any escapes.
-  return !foundEscapes;
+  // We succeeded if we reached this point since we handled all uses.
+  return true;
 }
 
 //===----------------------------------------------------------------------===//
@@ -380,11 +379,12 @@ bool MoveKillsCopyableValuesChecker::check() {
     // Then compute liveness.
     SWIFT_DEFER { livenessInfo.clear(); };
     livenessInfo.initDef(lexicalValue);
-    // We do not care if we find an escape. We just want to make sure that any
-    // non-escaping users obey our property. If the user does something unsafe
-    // that is on them to manage.
-    bool foundEscape = livenessInfo.compute();
-    (void)foundEscape;
+
+    // We only fail to optimize if for some reason we hit reborrows. This is
+    // temporary since we really should just ban reborrows in Raw SIL.
+    bool canOptimize = livenessInfo.compute();
+    if (!canOptimize)
+      continue;
 
     // Then look at all of our found consuming uses. See if any of these are
     // _move that are within the boundary.