Fix assert in generated direct property getter/setters due to removal of _cmd parameter.

This fixes a bug from https://reviews.llvm.org/D131424 that removed the implicit `_cmd` parameter as an argument to `objc_direct` method implementations. In many cases the generated getter/setter will call `objc_getProperty` or `objc_setProperty`, both of which require the selector of the getter/setter; since `_cmd` didn't automatically have backing storage, attempting to load the address asserted.

For direct property generated getters/setters, this now passes an undefined/uninitialized/poison value as the `_cmd` argument to `objc_getProperty`/`objc_setProperty`. Prior to removing the `_cmd` argument from the ABI of direct methods, it was left uninitialized/undefined; although references within hand-implemented methods would load the selector in the method prologue, generated getters/setters never did and just forwarded the undefined value that was passed as the argument.

This change keeps the generated code mostly similar to before, passing an uninitialized/undefined/poison value; for setters, the value argument may be moved to another register.

Added a test that triggers the assert prior to the implementation code.

Differential Revision: https://reviews.llvm.org/D135091

Author: mwyman

clang/lib/CodeGen/CGObjC.cpp

@@ -25,6 +25,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Analysis/ObjCARCUtil.h"
 #include "llvm/BinaryFormat/MachO.h"
+#include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/InlineAsm.h"
 using namespace clang;
@@ -1111,6 +1112,25 @@ static void emitCPPObjectAtomicGetterCall(CodeGenFunction &CGF,
                callee, ReturnValueSlot(), args);
 }
 
+// emitCmdValueForGetterSetterBody - Handle emitting the load necessary for
+// the `_cmd` selector argument for getter/setter bodies. For direct methods,
+// this returns an undefined/poison value; this matches behavior prior to `_cmd`
+// being removed from the direct method ABI as the getter/setter caller would
+// never load one. For non-direct methods, this emits a load of the implicit
+// `_cmd` storage.
+static llvm::Value *emitCmdValueForGetterSetterBody(CodeGenFunction &CGF,
+                                                   ObjCMethodDecl *MD) {
+  if (MD->isDirectMethod()) {
+    // Direct methods do not have a `_cmd` argument. Emit an undefined/poison
+    // value. This will be passed to objc_getProperty/objc_setProperty, which
+    // has not appeared bothered by the `_cmd` argument being undefined before.
+    llvm::Type *selType = CGF.ConvertType(CGF.getContext().getObjCSelType());
+    return llvm::PoisonValue::get(selType);
+  }
+
+  return CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(MD->getCmdDecl()), "cmd");
+}
+
 void
 CodeGenFunction::generateObjCGetterBody(const ObjCImplementationDecl *classImpl,
                                         const ObjCPropertyImplDecl *propImpl,
@@ -1189,8 +1209,7 @@ CodeGenFunction::generateObjCGetterBody(const ObjCImplementationDecl *classImpl,
     // Return (ivar-type) objc_getProperty((id) self, _cmd, offset, true).
     // FIXME: Can't this be simpler? This might even be worse than the
     // corresponding gcc code.
-    llvm::Value *cmd =
-      Builder.CreateLoad(GetAddrOfLocalVar(getterMethod->getCmdDecl()), "cmd");
+    llvm::Value *cmd = emitCmdValueForGetterSetterBody(*this, getterMethod);
     llvm::Value *self = Builder.CreateBitCast(LoadObjCSelf(), VoidPtrTy);
     llvm::Value *ivarOffset =
       EmitIvarOffset(classImpl->getClassInterface(), ivar);
@@ -1475,8 +1494,7 @@ CodeGenFunction::generateObjCSetterBody(const ObjCImplementationDecl *classImpl,
 
     // Emit objc_setProperty((id) self, _cmd, offset, arg,
     //                       <is-atomic>, <is-copy>).
-    llvm::Value *cmd =
-      Builder.CreateLoad(GetAddrOfLocalVar(setterMethod->getCmdDecl()));
+    llvm::Value *cmd = emitCmdValueForGetterSetterBody(*this, setterMethod);
     llvm::Value *self =
       Builder.CreateBitCast(LoadObjCSelf(), VoidPtrTy);
     llvm::Value *ivarOffset =

clang/test/CodeGenObjC/direct-method.m

@@ -14,6 +14,7 @@ @interface Root
 - (int)getInt __attribute__((objc_direct));
 @property(direct, readonly) int intProperty;
 @property(direct, readonly) int intProperty2;
+@property(direct, readonly) id objectProperty;
 @end
 
 @implementation Root
@@ -167,6 +168,15 @@ - (void)accessCmd __attribute__((objc_direct)) {
 @end
 // CHECK-LABEL: define hidden i32 @"\01-[Root intProperty]"
 
+// Check the synthesized objectProperty calls objc_getProperty(); this also
+// checks that the synthesized method passes undef for the `cmd` argument.
+// CHECK-LABEL: define hidden i8* @"\01-[Root objectProperty]"(
+// CHECK-LABEL: objc_direct_method.cont:
+// CHECK-NEXT: [[SELFVAL:%.*]] = load {{.*}} %self.addr,
+// CHECK-NEXT: [[SELF:%.*]] = bitcast {{.*}} [[SELFVAL]] to i8*
+// CHECK-NEXT: [[IVAR:%.*]] = load {{.*}} @"OBJC_IVAR_$_Root._objectProperty",
+// CHECK-NEXT: call i8* @objc_getProperty(i8* noundef [[SELF]], i8* noundef poison, i64 noundef [[IVAR]], {{.*}})
+
 @interface Foo : Root {
   id __strong _cause_cxx_destruct;
 }