Forward ns_consumed delegate arguments with a move.

StartFunction enters a release cleanup for ns_consumed arguments in
ARC, so we need to balance that somehow.  We could teach StartFunction
that it's emitting a delegating function, so that the cleanup is
unnecessary, but that would be invasive and somewhat fraught.  We could
balance the consumed argument with an extra retain, but clearing the
original variable should be easier to optimize and avoid some extra work
at -O0.  And there shouldn't be any difference as long as nothing else
uses the argument, which should always be true for the places we emit
delegate arguments.

Fixes PR 27887.

llvm-svn: 287291

1 files changed, 21 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 2fc16049f6b..54468d939d3 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2912,12 +2912,30 @@ void CodeGenFunction::EmitDelegateCallArg(CallArgList &args,
   assert(!isInAllocaArgument(CGM.getCXXABI(), type) &&
          "cannot emit delegate call arguments for inalloca arguments!");
 
+  // GetAddrOfLocalVar returns a pointer-to-pointer for references,
+  // but the argument needs to be the original pointer.
+  if (type->isReferenceType()) {
+    args.add(RValue::get(Builder.CreateLoad(local)), type);
+
+  // In ARC, move out of consumed arguments so that the release cleanup
+  // entered by StartFunction doesn't cause an over-release.  This isn't
+  // optimal -O0 code generation, but it should get cleaned up when
+  // optimization is enabled.  This also assumes that delegate calls are
+  // performed exactly once for a set of arguments, but that should be safe.
+  } else if (getLangOpts().ObjCAutoRefCount &&
+             param->hasAttr<NSConsumedAttr>() &&
+             type->isObjCRetainableType()) {
+    llvm::Value *ptr = Builder.CreateLoad(local);
+    auto null =
+      llvm::ConstantPointerNull::get(cast<llvm::PointerType>(ptr->getType()));
+    Builder.CreateStore(null, local);
+    args.add(RValue::get(ptr), type);
+
   // For the most part, we just need to load the alloca, except that
   // aggregate r-values are actually pointers to temporaries.
-  if (type->isReferenceType())
-    args.add(RValue::get(Builder.CreateLoad(local)), type);
-  else
+  } else {
     args.add(convertTempToRValue(local, type, loc), type);
+  }
 }
 
 static bool isProvablyNull(llvm::Value *addr) {