Insert end_borrow before any destroy_value while ending lifetime of a reborrow with dependencies

Author: meg-gupta

lib/SILOptimizer/Transforms/DeadCodeElimination.cpp

@@ -557,15 +557,32 @@ bool DCE::removeDead() {
         BranchesChanged = true;
         continue;
       }
+
+      auto *phiArg = cast<SILPhiArgument>(arg);
       // In OSSA, we have to delete a dead phi argument and insert destroy or
       // end_borrow at its predecessors if the incoming values are live.
       // This is not necessary in non-OSSA, and will infact be incorrect.
       // Because, passing a value as a phi argument does not imply end of
       // lifetime in non-OSSA.
       for (auto *pred : BB.getPredecessorBlocks()) {
         auto *predTerm = pred->getTerminator();
-        auto predArg = predTerm->getAllOperands()[i].get();
-        endLifetimeOfLiveValue(predArg, predTerm);
+        SILInstruction *insertPt = predTerm;
+        if (phiArg->getOwnershipKind() == OwnershipKind::Guaranteed) {
+          // If the phiArg is dead and had reborrow dependencies, its baseValue
+          // may also have been dead and a destroy_value of its baseValue may
+          // have been inserted before the pred's terminator. Make sure to
+          // adjust the insertPt before any destroy_value.
+          for (SILInstruction &predInst : llvm::reverse(*pred)) {
+            if (&predInst == predTerm)
+              continue;
+            if (!isa<DestroyValueInst>(&predInst)) {
+              insertPt = &*std::next(predInst.getIterator());
+              break;
+            }
+          }
+        }
+
+        endLifetimeOfLiveValue(phiArg->getIncomingPhiValue(pred), insertPt);
       }
       erasePhiArgument(&BB, i);
       Changed = true;

test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil

@@ -375,6 +375,91 @@ bb1(%copy2 : @owned $NonTrivialStruct, %borrow2 : @guaranteed $NonTrivialStruct)
   return %newcopy : $NonTrivialStruct
 }
 
+// CHECK-LABEL: sil [ossa] @dce_borrowlifetime2 :
+// CHECK: bb1:
+// CHECK-LABEL: } // end sil function 'dce_borrowlifetime2'
+sil [ossa] @dce_borrowlifetime2 : $@convention(thin) (@guaranteed Klass) -> () {
+bb0(%0 : @guaranteed $Klass):
+  %copy = copy_value %0 : $Klass
+  %borrow = begin_borrow %copy : $Klass
+  %2 = function_ref @$use_klass2 : $@convention(thin) (@guaranteed Klass) -> ()
+  %3 = apply %2(%borrow) : $@convention(thin) (@guaranteed Klass) -> ()
+  %5 = apply %2(%copy) : $@convention(thin) (@guaranteed Klass) -> ()
+  br bb1(%copy : $Klass, %borrow : $Klass)
+
+bb1(%copy2 : @owned $Klass, %borrow2 : @guaranteed $Klass):
+  end_borrow %borrow2 : $Klass
+  destroy_value %copy2 : $Klass
+  %res = tuple ()
+  return %res : $()
+}
+
+// CHECK-LABEL: sil [ossa] @dce_borrowlifetime3 :
+// CHECK: bb1:
+// CHECK-LABEL: } // end sil function 'dce_borrowlifetime3'
+sil [ossa] @dce_borrowlifetime3 : $@convention(thin) (@guaranteed Klass) -> () {
+bb0(%0 : @guaranteed $Klass):
+  %copy = copy_value %0 : $Klass
+  %borrow = begin_borrow %copy : $Klass
+  %2 = function_ref @$use_klass2 : $@convention(thin) (@guaranteed Klass) -> ()
+  %3 = apply %2(%borrow) : $@convention(thin) (@guaranteed Klass) -> ()
+  %5 = apply %2(%copy) : $@convention(thin) (@guaranteed Klass) -> ()
+  br bb1(%borrow : $Klass, %copy : $Klass)
+
+bb1(%borrow2 : @guaranteed $Klass, %copy2 : @owned $Klass):
+  end_borrow %borrow2 : $Klass
+  destroy_value %copy2 : $Klass
+  %res = tuple ()
+  return %res : $()
+}
+
+// CHECK-LABEL: sil [ossa] @dce_borrowlifetime4 :
+// CHECK: bb1:
+// CHECK-LABEL: } // end sil function 'dce_borrowlifetime4'
+sil [ossa] @dce_borrowlifetime4 : $@convention(thin) (@guaranteed Klass) -> () {
+bb0(%0 : @guaranteed $Klass):
+  %copy = copy_value %0 : $Klass
+  %borrow = begin_borrow %copy : $Klass
+  %2 = function_ref @$use_klass2 : $@convention(thin) (@guaranteed Klass) -> ()
+  %3 = apply %2(%borrow) : $@convention(thin) (@guaranteed Klass) -> ()
+  %5 = apply %2(%copy) : $@convention(thin) (@guaranteed Klass) -> ()
+  br bb1(%borrow : $Klass)
+
+bb1(%borrow2 : @guaranteed $Klass):
+  end_borrow %borrow2 : $Klass
+  br bb2(%copy : $Klass)
+
+bb2(%copy2 : @owned $Klass):
+  destroy_value %copy2 : $Klass
+  %res = tuple ()
+  return %res : $()
+}
+
+// CHECK-LABEL: sil [ossa] @dce_borrowlifetime5 :
+// CHECK: bb1:
+// CHECK-LABEL: } // end sil function 'dce_borrowlifetime5'
+sil [ossa] @dce_borrowlifetime5 : $@convention(thin) (@guaranteed Klass) -> () {
+bb0(%0 : @guaranteed $Klass):
+  %copy1 = copy_value %0 : $Klass
+  %copy2 = copy_value %0 : $Klass
+  %borrow1 = begin_borrow %copy1 : $Klass
+  %borrow2 = begin_borrow %copy2 : $Klass
+  %2 = function_ref @$use_klass2 : $@convention(thin) (@guaranteed Klass) -> ()
+  %3 = apply %2(%borrow1) : $@convention(thin) (@guaranteed Klass) -> ()
+  %4 = apply %2(%borrow2) : $@convention(thin) (@guaranteed Klass) -> ()
+  %5 = apply %2(%copy1) : $@convention(thin) (@guaranteed Klass) -> ()
+  %6 = apply %2(%copy2) : $@convention(thin) (@guaranteed Klass) -> ()
+  br bb1(%copy1 : $Klass, %borrow1 : $Klass, %borrow2 : $Klass)
+
+bb1(%newcopy : @owned $Klass, %newborrow1 : @guaranteed $Klass, %newborrow2 : @guaranteed $Klass):
+  end_borrow %newborrow1 : $Klass
+  end_borrow %newborrow2 : $Klass
+  destroy_value %newcopy : $Klass
+  destroy_value %copy2 : $Klass
+  %res = tuple ()
+  return %res : $()
+}
+
 // CHECK-LABEL: sil [ossa] @infinite_loop :
 // CHECK-NOT: copy_value
 // CHECK-LABEL: } // end sil function 'infinite_loop'