[arcmt] Remove an unused -autorelease, without failing with error, for this

idiom that is used commonly in setters:

   [backingValue autorelease];
   backingValue = [newValue retain]; // in general a +1 assign

rdar://9914061

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157347 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 129 insertions, 18 deletions

diff --git a/lib/ARCMigrate/TransProperties.cpp b/lib/ARCMigrate/TransProperties.cpp
index 8f65fc3a8b..5ec918fe93 100644
--- a/lib/ARCMigrate/TransProperties.cpp
+++ b/lib/ARCMigrate/TransProperties.cpp
@@ -309,17 +309,8 @@ private:
         if (RE->getDecl() != Ivar)
           return true;
 
-      if (ObjCMessageExpr *
-            ME = dyn_cast<ObjCMessageExpr>(E->getRHS()->IgnoreParenCasts()))
-        if (ME->getMethodFamily() == OMF_retain)
+        if (isPlusOneAssign(E))
           return false;
-
-      ImplicitCastExpr *implCE = dyn_cast<ImplicitCastExpr>(E->getRHS());
-      while (implCE && implCE->getCastKind() ==  CK_BitCast)
-        implCE = dyn_cast<ImplicitCastExpr>(implCE->getSubExpr());
-
-      if (implCE && implCE->getCastKind() == CK_ARCConsumeObject)
-        return false;
       }
 
       return true;
diff --git a/lib/ARCMigrate/TransRetainReleaseDealloc.cpp b/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
index 11a6553341..df3cd5858e 100644
--- a/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
+++ b/lib/ARCMigrate/TransRetainReleaseDealloc.cpp
@@ -64,14 +64,16 @@ public:
       return true;
     case OMF_autorelease:
       if (isRemovable(E)) {
-        // An unused autorelease is badness. If we remove it the receiver
-        // will likely die immediately while previously it was kept alive
-        // by the autorelease pool. This is bad practice in general, leave it
-        // and emit an error to force the user to restructure his code.
-        Pass.TA.reportError("it is not safe to remove an unused 'autorelease' "
-            "message; its receiver may be destroyed immediately",
-            E->getLocStart(), E->getSourceRange());
-        return true;
+        if (!isCommonUnusedAutorelease(E)) {
+          // An unused autorelease is badness. If we remove it the receiver
+          // will likely die immediately while previously it was kept alive
+          // by the autorelease pool. This is bad practice in general, leave it
+          // and emit an error to force the user to restructure his code.
+          Pass.TA.reportError("it is not safe to remove an unused 'autorelease' "
+              "message; its receiver may be destroyed immediately",
+              E->getLocStart(), E->getSourceRange());
+          return true;
+        }
       }
       // Pass through.
     case OMF_retain:
@@ -156,6 +158,80 @@ public:
   }
 
 private:
+  /// \brief Checks for idioms where an unused -autorelease is common.
+  ///
+  /// Currently only returns true for this idiom which is common in property
+  /// setters:
+  ///
+  ///   [backingValue autorelease];
+  ///   backingValue = [newValue retain]; // in general a +1 assign
+  ///
+  bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
+    Expr *Rec = E->getInstanceReceiver();
+    if (!Rec)
+      return false;
+
+    Decl *RefD = getReferencedDecl(Rec);
+    if (!RefD)
+      return false;
+
+    Stmt *OuterS = E, *InnerS;
+    do {
+      InnerS = OuterS;
+      OuterS = StmtMap->getParent(InnerS);
+    }
+    while (OuterS && (isa<ParenExpr>(OuterS) ||
+                      isa<CastExpr>(OuterS) ||
+                      isa<ExprWithCleanups>(OuterS)));
+    
+    if (!OuterS)
+      return false;
+
+    // Find next statement after the -autorelease.
+
+    Stmt::child_iterator currChildS = OuterS->child_begin();
+    Stmt::child_iterator childE = OuterS->child_end();
+    for (; currChildS != childE; ++currChildS) {
+      if (*currChildS == InnerS)
+        break;
+    }
+    if (currChildS == childE)
+      return false;
+    ++currChildS;
+    if (currChildS == childE)
+      return false;
+
+    Stmt *nextStmt = *currChildS;
+    if (!nextStmt)
+      return false;
+    nextStmt = nextStmt->IgnoreImplicit();
+
+    // Check for "RefD = [+1 retained object];".
+    
+    if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(nextStmt)) {
+      if (RefD != getReferencedDecl(Bop->getLHS()))
+        return false;
+      if (isPlusOneAssign(Bop))
+        return true;
+    }
+    return false;
+  }
+
+  Decl *getReferencedDecl(Expr *E) {
+    if (!E)
+      return 0;
+
+    E = E->IgnoreParenCasts();
+    if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
+      return DRE->getDecl();
+    if (MemberExpr *ME = dyn_cast<MemberExpr>(E))
+      return ME->getMemberDecl();
+    if (ObjCIvarRefExpr *IRE = dyn_cast<ObjCIvarRefExpr>(E))
+      return IRE->getDecl();
+
+    return 0;
+  }
+
   /// \brief Check if the retain/release is due to a GCD/XPC macro that are
   /// defined as:
   ///
diff --git a/lib/ARCMigrate/Transforms.cpp b/lib/ARCMigrate/Transforms.cpp
index 50bea95f12..24b650561c 100644
--- a/lib/ARCMigrate/Transforms.cpp
+++ b/lib/ARCMigrate/Transforms.cpp
@@ -14,6 +14,7 @@
 #include "clang/AST/StmtVisitor.h"
 #include "clang/Lex/Lexer.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Analysis/DomainSpecific/CocoaConventions.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/DenseSet.h"
 #include <map>
@@ -56,6 +57,47 @@ bool trans::canApplyWeak(ASTContext &Ctx, QualType type,
   return true;
 }
 
+bool trans::isPlusOneAssign(const BinaryOperator *E) {
+  if (E->getOpcode() != BO_Assign)
+    return false;
+
+  if (const ObjCMessageExpr *
+        ME = dyn_cast<ObjCMessageExpr>(E->getRHS()->IgnoreParenCasts()))
+    if (ME->getMethodFamily() == OMF_retain)
+      return true;
+
+  if (const CallExpr *
+        callE = dyn_cast<CallExpr>(E->getRHS()->IgnoreParenCasts())) {
+    if (const FunctionDecl *FD = callE->getDirectCallee()) {
+      if (FD->getAttr<CFReturnsRetainedAttr>())
+        return true;
+
+      if (FD->isGlobal() &&
+          FD->getIdentifier() &&
+          FD->getParent()->isTranslationUnit() &&
+          FD->getLinkage() == ExternalLinkage &&
+          ento::cocoa::isRefType(callE->getType(), "CF",
+                                 FD->getIdentifier()->getName())) {
+        StringRef fname = FD->getIdentifier()->getName();
+        if (fname.endswith("Retain") ||
+            fname.find("Create") != StringRef::npos ||
+            fname.find("Copy") != StringRef::npos) {
+          return true;
+        }
+      }
+    }
+  }
+
+  const ImplicitCastExpr *implCE = dyn_cast<ImplicitCastExpr>(E->getRHS());
+  while (implCE && implCE->getCastKind() ==  CK_BitCast)
+    implCE = dyn_cast<ImplicitCastExpr>(implCE->getSubExpr());
+
+  if (implCE && implCE->getCastKind() == CK_ARCConsumeObject)
+    return true;
+
+  return false;
+}
+
 /// \brief 'Loc' is the end of a statement range. This returns the location
 /// immediately after the semicolon following the statement.
 /// If no semicolon is found or the location is inside a macro, the returned
diff --git a/lib/ARCMigrate/Transforms.h b/lib/ARCMigrate/Transforms.h
index 445c3e599d..7abc0304b1 100644
--- a/lib/ARCMigrate/Transforms.h
+++ b/lib/ARCMigrate/Transforms.h
@@ -154,6 +154,8 @@ public:
 bool canApplyWeak(ASTContext &Ctx, QualType type,
                   bool AllowOnUnknownClass = false);
 
+bool isPlusOneAssign(const BinaryOperator *E);
+
 /// \brief 'Loc' is the end of a statement range. This returns the location
 /// immediately after the semicolon following the statement.
 /// If no semicolon is found or the location is inside a macro, the returned