[CopyPropagation] Run LexicalDestroyFolding.

Author: nate-chandler

lib/SILOptimizer/Transforms/CopyPropagation.cpp

@@ -434,21 +434,50 @@ void CopyPropagation::run() {
     }
   }
 
+  // canonicalizer performs all modifications through deleter's callbacks, so we
+  // don't need to explicitly check for changes.
+  CanonicalizeOSSALifetime canonicalizer(pruneDebug, poisonRefs,
+                                         accessBlockAnalysis, domTree, deleter);
+
   // NOTE: We assume that the function is in reverse post order so visiting the
   //       blocks and pushing begin_borrows as we see them and then popping them
   //       off the end will result in shrinking inner borrow scopes first.
   while (auto *bbi = beginBorrowsToShrink.pop()) {
-    SmallVector<CopyValueInst *, 4> modifiedCopyValueInsts;
-    changed |= shrinkBorrowScope(bbi, deleter, modifiedCopyValueInsts);
-    for (auto *cvi : modifiedCopyValueInsts)
-      defWorklist.updateForCopy(cvi);
+    bool firstRun = true;
+    // Run the sequence of utilities:
+    // - ShrinkBorrowScope
+    // - CanonicalizeOSSALifetime
+    // - LexicalDestroyFolder
+    // at least once and then until each stops making changes.
+    while (true) {
+      SmallVector<CopyValueInst *, 4> modifiedCopyValueInsts;
+      auto shrunk = shrinkBorrowScope(bbi, deleter, modifiedCopyValueInsts);
+      for (auto *cvi : modifiedCopyValueInsts)
+        defWorklist.updateForCopy(cvi);
+      changed |= shrunk;
+      if (!shrunk && !firstRun)
+        break;
+
+      // If borrowed value is not owned, neither CanonicalizeOSSALifetime nor
+      // LexicalDestroyFolding will do anything with it.  Just bail out now.
+      auto borrowee = bbi->getOperand();
+      if (borrowee.getOwnershipKind() != OwnershipKind::Owned)
+        break;
+
+      auto canonicalized = canonicalizer.canonicalizeValueLifetime(borrowee);
+      if (!canonicalized && !firstRun)
+        break;
+
+      auto folded = foldDestroysOfCopiedLexicalBorrow(bbi, *domTree, deleter);
+      if (!folded)
+        break;
+      // We don't add the produced move_value instruction to the worklist
+      // because it can't handle propagation.
+      firstRun = false;
+    }
   }
   deleter.cleanupDeadInstructions();
 
-  // canonicalizer performs all modifications through deleter's callbacks, so we
-  // don't need to explicitly check for changes.
-  CanonicalizeOSSALifetime canonicalizer(pruneDebug, poisonRefs,
-                                         accessBlockAnalysis, domTree, deleter);
   // For now, only modify forwarding instructions
   // At -Onone, we do nothing but rewrite copies of owned values.
   if (canonicalizeBorrows) {

test/SILOptimizer/shrink_borrow_scope.sil

@@ -777,13 +777,14 @@ bad(%15 : @owned $Error):
 // CHECK:       [[LEFT]]:
 // CHECK:         [[REGISTER_3:%[^,]+]] = apply undef()
 // CHECK:         end_borrow [[LIFETIME]]
+// CHECK:         destroy_value [[INSTANCE]]
 // CHECK:         br [[EXIT:bb[0-9]+]]
 // CHECK:       [[RIGHT]]:
 // CHECK:         [[REGISTER_6:%[^,]+]] = apply undef()
 // CHECK:         end_borrow [[LIFETIME]]
+// CHECK:         destroy_value [[INSTANCE]]
 // CHECK:         br [[EXIT]]
 // CHECK:       [[EXIT]]:
-// CHECK:         destroy_value [[INSTANCE]]
 // CHECK-LABEL: } // end sil function 'hoist_up_to_two_barrier_applies'
 sil [ossa] @hoist_up_to_two_barrier_applies : $@convention(thin) (@owned C) -> () {
 entry(%instance : @owned $C):