[SemanticARC] NFC: Extracted opt from visit.

In preparation to attempt two variations of the optimization, added
performLoadCopyToLoadBorrowOptimization and call it from visitLoadInst.

Author: nate-chandler

lib/SILOptimizer/SemanticARC/LoadCopyToLoadBorrowOpt.cpp

@@ -319,8 +319,6 @@ static bool isWrittenTo(Context &ctx, LoadInst *load,
 //                            Top Level Entrypoint
 //===----------------------------------------------------------------------===//
 
-// Convert a load [copy] from unique storage [read] that has all uses that can
-// accept a guaranteed parameter to a load_borrow.
 bool SemanticARCOptVisitor::visitLoadInst(LoadInst *li) {
   // This optimization can use more complex analysis. We should do some
   // experiments before enabling this by default as a guaranteed optimization.
@@ -334,9 +332,19 @@ bool SemanticARCOptVisitor::visitLoadInst(LoadInst *li) {
   if (li->getOwnershipQualifier() != LoadOwnershipQualifier::Copy)
     return false;
 
-  // Ok, we have our load [copy]. Make sure its value is truly a dead live range
-  // implying it is only ever consumed by destroy_value instructions. If it is
-  // consumed, we need to pass off a +1 value, so bail.
+  // Ok, we have our load [copy].  Try to optimize.
+  return performLoadCopyToLoadBorrowOptimization(li);
+}
+
+// Convert a load [copy] from unique storage [read] that has all uses that can
+// accept a guaranteed parameter to a load_borrow.
+bool SemanticARCOptVisitor::performLoadCopyToLoadBorrowOptimization(
+    LoadInst *li) {
+  assert(li->getOwnershipQualifier() == LoadOwnershipQualifier::Copy);
+
+  // Make sure its value is truly a dead live range implying it is only ever
+  // consumed by destroy_value instructions. If it is consumed, we need to pass
+  // off a +1 value, so bail.
   //
   // FIXME: We should consider if it is worth promoting a load [copy]
   // -> load_borrow if we can put a copy_value on a cold path and thus
@@ -355,8 +363,8 @@ bool SemanticARCOptVisitor::visitLoadInst(LoadInst *li) {
   // load_borrow.
   auto *lbi =
       SILBuilderWithScope(li).createLoadBorrow(li->getLoc(), li->getOperand());
-
   lr.insertEndBorrowsAtDestroys(lbi, getDeadEndBlocks(), ctx.lifetimeFrontier);
-  std::move(lr).convertToGuaranteedAndRAUW(lbi, getCallbacks());
+  SILValue replacement = lbi;
+  std::move(lr).convertToGuaranteedAndRAUW(replacement, getCallbacks());
   return true;
 }

lib/SILOptimizer/SemanticARC/SemanticARCOptVisitor.h

@@ -202,6 +202,7 @@ struct LLVM_LIBRARY_VISIBILITY SemanticARCOptVisitor
   bool optimize();
   bool optimizeWithoutFixedPoint();
 
+  bool performLoadCopyToLoadBorrowOptimization(LoadInst *li);
   bool performGuaranteedCopyValueOptimization(CopyValueInst *cvi);
   bool eliminateDeadLiveRangeCopyValue(CopyValueInst *cvi);
   bool tryJoiningCopyValueLiveRangeWithOperand(CopyValueInst *cvi);