[clang] Fix Objective-C++ Sret of non-trivial data types on Windows ARM64 (PR #88671)

[David Chisnall via cfe-commits]

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@@ -2911,12 +2911,25 @@ CGObjCGNU::GenerateMessageSend(CodeGenFunction &CGF,
                                       "objc_msgSend_fpret")
                 .getCallee();
       } else if (CGM.ReturnTypeUsesSRet(MSI.CallInfo)) {
+        StringRef name = "objc_msgSend_stret";
+
+        // The address of the memory block is be passed in x8 for POD type,
+        // or in x0 for non-POD type (marked as inreg).
+        bool shouldCheckForInReg =
+            CGM.getContext()
+                .getTargetInfo()
+                .getTriple()
+                .isWindowsMSVCEnvironment() &&
+            CGM.getContext().getTargetInfo().getTriple().isAArch64();
+        if (shouldCheckForInReg && CGM.ReturnTypeHasInReg(MSI.CallInfo)) {
+          name = "objc_msgSend_stret2_np";
+        }
+
         // The actual types here don't matter - we're going to bitcast the
         // function anyway
-        imp =
-            CGM.CreateRuntimeFunction(llvm::FunctionType::get(IdTy, IdTy, true),
-                                      "objc_msgSend_stret")
-                .getCallee();
+        imp = CGM.CreateRuntimeFunction(
+                     llvm::FunctionType::get(IdTy, IdTy, true), name)
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davidchisnall wrote:

If you're making this generic over `name`, it would be nice to pull the `objc_msgSend` case (next one down) out as well.

https://github.com/llvm/llvm-project/pull/88671