From e7b3b94cf500c5c4dc1bed6dd47e031d73678c86 Mon Sep 17 00:00:00 2001
From: Arvind Mukund <MasterAwesome@users.noreply.github.com>
Date: Thu, 5 Oct 2023 12:01:56 -0700
Subject: [PATCH] [clang] Correct behavior of `LLVM_UNREACHABLE_OPTIMIZE=OFF`
 for `Release` builds (#68284)

```c++
AArch64SVEPcsAttr *AArch64SVEPcsAttr::CreateImplicit(ASTContext &Ctx, SourceRange Range, Spelling S) {
  AttributeCommonInfo I(Range, NoSemaHandlerAttribute, (
    S == GNU_aarch64_sve_pcs ? AttributeCommonInfo::Form{AttributeCommonInfo::AS_GNU, GNU_aarch64_sve_pcs, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/} :
    S == CXX11_clang_aarch64_sve_pcs ? AttributeCommonInfo::Form{AttributeCommonInfo::AS_CXX11, CXX11_clang_aarch64_sve_pcs, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/} :
    S == C23_clang_aarch64_sve_pcs ? AttributeCommonInfo::Form{AttributeCommonInfo::AS_C23, C23_clang_aarch64_sve_pcs, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/} :
    (llvm_unreachable("Unknown attribute spelling!"),  AttributeCommonInfo::Form{AttributeCommonInfo::AS_GNU, 0, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/})));
  return CreateImplicit(Ctx, I);
}
```

```c++
AArch64SVEPcsAttr *AArch64SVEPcsAttr::CreateImplicit(ASTContext &Ctx, SourceRange Range, Spelling S) {
  AttributeCommonInfo I(Range, NoSemaHandlerAttribute, [&]() {
    switch (S) {
    case GNU_aarch64_sve_pcs:
      return AttributeCommonInfo::Form{AttributeCommonInfo::AS_GNU, GNU_aarch64_sve_pcs, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/};
    case CXX11_clang_aarch64_sve_pcs:
      return AttributeCommonInfo::Form{AttributeCommonInfo::AS_CXX11, CXX11_clang_aarch64_sve_pcs, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/};
    case C23_clang_aarch64_sve_pcs:
      return AttributeCommonInfo::Form{AttributeCommonInfo::AS_C23, C23_clang_aarch64_sve_pcs, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/};
    default:
      llvm_unreachable("Unknown attribute spelling!");
      return AttributeCommonInfo::Form{AttributeCommonInfo::AS_GNU, 0, false /*IsAlignas*/, false /*IsRegularKeywordAttribute*/};
    }
  }());
  return CreateImplicit(Ctx, I);
}
```

Fixes https://github.com/llvm/llvm-project/issues/68237
Conflicts:
	clang/docs/ReleaseNotes.rst
---
 clang/docs/ReleaseNotes.rst               |  2 ++
 clang/utils/TableGen/ClangAttrEmitter.cpp | 17 +++++++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ee3794f7fc61..3323c6ceb2bc 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -717,6 +717,8 @@ Bug Fixes in This Version
   virtual member functions even if the target required a greater function
   alignment and/or did not have function pointers which point to function entry
   points (i.e., uses function descriptor objects instead).
+- Fixes a ``clang-17`` regression where ``LLVM_UNREACHABLE_OPTIMIZE=OFF``
+  cannot be used with ``Release`` mode builds. (`#68237 <https://github.com/llvm/llvm-project/issues/68237>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/utils/TableGen/ClangAttrEmitter.cpp b/clang/utils/TableGen/ClangAttrEmitter.cpp
index 8ef728f86c6b..b5813c6abc2b 100644
--- a/clang/utils/TableGen/ClangAttrEmitter.cpp
+++ b/clang/utils/TableGen/ClangAttrEmitter.cpp
@@ -2639,7 +2639,8 @@ static void emitAttributes(RecordKeeper &Records, raw_ostream &OS,
         OS << ", ";
         emitFormInitializer(OS, Spellings[0], "0");
       } else {
-        OS << ", (\n";
+        OS << ", [&]() {\n";
+        OS << "    switch (S) {\n";
         std::set<std::string> Uniques;
         unsigned Idx = 0;
         for (auto I = Spellings.begin(), E = Spellings.end(); I != E;
@@ -2647,15 +2648,19 @@ static void emitAttributes(RecordKeeper &Records, raw_ostream &OS,
           const FlattenedSpelling &S = *I;
           const auto &Name = SemanticToSyntacticMap[Idx];
           if (Uniques.insert(Name).second) {
-            OS << "    S == " << Name << " ? AttributeCommonInfo::Form";
+            OS << "    case " << Name << ":\n";
+            OS << "      return AttributeCommonInfo::Form";
             emitFormInitializer(OS, S, Name);
-            OS << " :\n";
+            OS << ";\n";
           }
         }
-        OS << "    (llvm_unreachable(\"Unknown attribute spelling!\"), "
-           << " AttributeCommonInfo::Form";
+        OS << "    default:\n";
+        OS << "      llvm_unreachable(\"Unknown attribute spelling!\");\n"
+           << "      return AttributeCommonInfo::Form";
         emitFormInitializer(OS, Spellings[0], "0");
-        OS << "))";
+        OS << ";\n"
+           << "    }\n"
+           << "  }()";
       }
 
       OS << ");\n";