From 94c3b169785c0a0ae650c724dcf2c22ff65f5e24 Mon Sep 17 00:00:00 2001
From: David Chisnall <github@theravensnest.org>
Date: Sun, 24 Jul 2022 11:56:12 +0100
Subject: [PATCH] Fix crash in ObjC codegen introduced with
 5ab6ee75994d645725264e757d67bbb1c96fb2b6

5ab6ee75994d645725264e757d67bbb1c96fb2b6 assumed that if `RValue::isScalar()` returns true then `RValue::getScalarVal` will return a valid value.  This is not the case when the return value is `void` and so void message returns would crash if they hit this path.  This is triggered only for cases where the nil-handling path needs to do something non-trivial (destroy arguments that should be consumed by the callee).

Reviewed By: triplef

Differential Revision: https://reviews.llvm.org/D123898
---
 clang/lib/CodeGen/CGObjCGNU.cpp                    | 12 +++++++-----
 .../gnustep2-nontrivial-destructor-argument.mm     | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+), 5 deletions(-)
 create mode 100644 clang/test/CodeGenObjC/gnustep2-nontrivial-destructor-argument.mm

diff --git a/clang/lib/CodeGen/CGObjCGNU.cpp b/clang/lib/CodeGen/CGObjCGNU.cpp
index ec459f0..7bbe9af 100644
--- a/clang/lib/CodeGen/CGObjCGNU.cpp
+++ b/clang/lib/CodeGen/CGObjCGNU.cpp
@@ -2837,11 +2837,13 @@ CGObjCGNU::GenerateMessageSend(CodeGenFunction &CGF,
     // Enter the continuation block and emit a phi if required.
     CGF.EmitBlock(continueBB);
     if (msgRet.isScalar()) {
-      llvm::Value *v = msgRet.getScalarVal();
-      llvm::PHINode *phi = Builder.CreatePHI(v->getType(), 2);
-      phi->addIncoming(v, nonNilPathBB);
-      phi->addIncoming(CGM.EmitNullConstant(ResultType), nilPathBB);
-      msgRet = RValue::get(phi);
+      // If the return type is void, do nothing
+      if (llvm::Value *v = msgRet.getScalarVal()) {
+        llvm::PHINode *phi = Builder.CreatePHI(v->getType(), 2);
+        phi->addIncoming(v, nonNilPathBB);
+        phi->addIncoming(CGM.EmitNullConstant(ResultType), nilPathBB);
+        msgRet = RValue::get(phi);
+      }
     } else if (msgRet.isAggregate()) {
       // Aggregate zeroing is handled in nilCleanupBB when it's required.
     } else /* isComplex() */ {
diff --git a/clang/test/CodeGenObjC/gnustep2-nontrivial-destructor-argument.mm b/clang/test/CodeGenObjC/gnustep2-nontrivial-destructor-argument.mm
new file mode 100644
index 0000000..a7de79b
--- /dev/null
+++ b/clang/test/CodeGenObjC/gnustep2-nontrivial-destructor-argument.mm
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -triple x86_64-unknow-windows-msvc -S -emit-llvm -fobjc-runtime=gnustep-2.0 -o - %s 
+
+// Regression test.  Ensure that C++ arguments with non-trivial destructors
+// don't crash the compiler.
+
+struct X
+{
+  int a;
+  ~X();
+};
+
+@protocol Y
+- (void)foo: (X)bar;
+@end
+
+
+void test(id<Y> obj)
+{
+  X a{12};
+  [obj foo: a];
+}
+
-- 
2.7.4