ARC: fix epilog-release-matcher. It has to handle dealloc_ref instructions.

This fixes a problem which might result in converting the owned self argument of a deallocating deinitializer into a guaranteed argument.

rdar://problem/28096460

Author: eeckstein

lib/SILOptimizer/Analysis/ARCAnalysis.cpp

@@ -777,6 +777,11 @@ collectMatchingReleases(SILBasicBlock *BB) {
   for (auto II = std::next(BB->rbegin()), IE = BB->rend(); II != IE; ++II) {
     // If we do not have a release_value or strong_release. We can continue
     if (!isa<ReleaseValueInst>(*II) && !isa<StrongReleaseInst>(*II)) {
+
+      // We cannot match a final release if it is followed by a dealloc_ref.
+      if (isa<DeallocRefInst>(*II))
+        break;
+
       // We do not know what this instruction is, do a simple check to make sure
       // that it does not decrement the reference count of any of its operand. 
       //

test/SILOptimizer/epilogue_release_dumper.sil

@@ -94,6 +94,19 @@ bb0(%0 : $foo, %1 : $*foo):
   return %3 : $()
 }
 
+// CHECK-LABEL: START: sil @dealloc_ref_after_last_release
+// CHECK: [[IN1:%.*]] = argument of bb0 : $foo
+// CHECK-NOT: strong_release [[IN1]] : $foo
+// CHECK: END: sil @dealloc_ref_after_last_release
+sil @dealloc_ref_after_last_release : $@convention(thin) (@owned foo) -> () {
+bb0(%0 : $foo):
+  strong_retain %0 : $foo
+  strong_release %0 : $foo
+  dealloc_ref %0 : $foo
+  %3 = tuple ()
+  return %3 : $()
+}
+
 // CHECK-LABEL: START: sil @single_release_bar
 // CHECK: [[IN1:%.*]] = argument of bb0 : $bar
 // CHECK: strong_release [[IN1]] : $bar