[objc] Don't require null-check and don't emit memset when result is ignored for struct-returning method calls [clang part]

This fixes an issue with the emission of lifetime markers for struct-returning Obj-C msgSend calls. When the result of a struct-returning call is ignored, the temporary storage is only marked with lifetime markers in one of the two branches of the nil-receiver-check. The check is, however, not required when the result is unused. If we still need to emit the check (due to consumer arguments), let's not emit the memset to zero out the result if it's unused. This fixes a use-after-scope false positive with AddressSanitizer.

Differential Revision: https://reviews.llvm.org/D34834

llvm-svn: 306837

1 files changed, 22 insertions, 11 deletions

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index 224d2d6606a..98435fefbd2 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -1678,7 +1678,10 @@ struct NullReturnState {
 
   /// Complete the null-return operation.  It is valid to call this
   /// regardless of whether 'init' has been called.
-  RValue complete(CodeGenFunction &CGF, RValue result, QualType resultType,
+  RValue complete(CodeGenFunction &CGF,
+                  ReturnValueSlot returnSlot,
+                  RValue result,
+                  QualType resultType,
                   const CallArgList &CallArgs,
                   const ObjCMethodDecl *Method) {
     // If we never had to do a null-check, just use the raw result.
@@ -1745,7 +1748,8 @@ struct NullReturnState {
     // memory or (2) agg values in registers.
     if (result.isAggregate()) {
       assert(result.isAggregate() && "null init of non-aggregate result?");
-      CGF.EmitNullInitialization(result.getAggregateAddress(), resultType);
+      if (!returnSlot.isUnused())
+        CGF.EmitNullInitialization(result.getAggregateAddress(), resultType);
       if (contBB) CGF.EmitBlock(contBB);
       return result;
     }
@@ -2117,11 +2121,11 @@ CGObjCCommonMac::EmitMessageSend(CodeGen::CodeGenFunction &CGF,
     }
   }
 
-  NullReturnState nullReturn;
+  bool RequiresNullCheck = false;
 
   llvm::Constant *Fn = nullptr;
   if (CGM.ReturnSlotInterferesWithArgs(MSI.CallInfo)) {
-    if (ReceiverCanBeNull) nullReturn.init(CGF, Arg0);
+    if (ReceiverCanBeNull) RequiresNullCheck = true;
     Fn = (ObjCABI == 2) ?  ObjCTypes.getSendStretFn2(IsSuper)
       : ObjCTypes.getSendStretFn(IsSuper);
   } else if (CGM.ReturnTypeUsesFPRet(ResultType)) {
@@ -2134,23 +2138,30 @@ CGObjCCommonMac::EmitMessageSend(CodeGen::CodeGenFunction &CGF,
     // arm64 uses objc_msgSend for stret methods and yet null receiver check
     // must be made for it.
     if (ReceiverCanBeNull && CGM.ReturnTypeUsesSRet(MSI.CallInfo))
-      nullReturn.init(CGF, Arg0);
+      RequiresNullCheck = true;
     Fn = (ObjCABI == 2) ? ObjCTypes.getSendFn2(IsSuper)
       : ObjCTypes.getSendFn(IsSuper);
   }
 
+  // We don't need to emit a null check to zero out an indirect result if the
+  // result is ignored.
+  if (Return.isUnused())
+    RequiresNullCheck = false;
+
   // Emit a null-check if there's a consumed argument other than the receiver.
-  bool RequiresNullCheck = false;
-  if (ReceiverCanBeNull && CGM.getLangOpts().ObjCAutoRefCount && Method) {
+  if (!RequiresNullCheck && CGM.getLangOpts().ObjCAutoRefCount && Method) {
     for (const auto *ParamDecl : Method->parameters()) {
       if (ParamDecl->hasAttr<NSConsumedAttr>()) {
-        if (!nullReturn.NullBB)
-          nullReturn.init(CGF, Arg0);
         RequiresNullCheck = true;
         break;
       }
     }
   }
+
+  NullReturnState nullReturn;
+  if (RequiresNullCheck) {
+    nullReturn.init(CGF, Arg0);
+  }
   
   llvm::Instruction *CallSite;
   Fn = llvm::ConstantExpr::getBitCast(Fn, MSI.MessengerType);
@@ -2164,7 +2175,7 @@ CGObjCCommonMac::EmitMessageSend(CodeGen::CodeGenFunction &CGF,
     llvm::CallSite(CallSite).setDoesNotReturn();
   }
 
-  return nullReturn.complete(CGF, rvalue, ResultType, CallArgs,
+  return nullReturn.complete(CGF, Return, rvalue, ResultType, CallArgs,
                              RequiresNullCheck ? Method : nullptr);
 }
 
@@ -7073,7 +7084,7 @@ CGObjCNonFragileABIMac::EmitVTableMessageSend(CodeGenFunction &CGF,
   CGCallee callee(CGCalleeInfo(), calleePtr);
 
   RValue result = CGF.EmitCall(MSI.CallInfo, callee, returnSlot, args);
-  return nullReturn.complete(CGF, result, resultType, formalArgs,
+  return nullReturn.complete(CGF, returnSlot, result, resultType, formalArgs,
                              requiresnullCheck ? method : nullptr);
 }