Add support for requiring Win x64 Unwind V2

Author: dpaoliello

clang/include/clang/Basic/CodeGenOptions.def

@@ -481,8 +481,10 @@ CODEGENOPT(StaticClosure, 1, 0)
 /// Assume that UAVs/SRVs may alias
 CODEGENOPT(ResMayAlias, 1, 0)
 
-/// Enables unwind v2 (epilog) information for x64 Windows.
-CODEGENOPT(WinX64EHUnwindV2, 1, 0)
+/// Controls how unwind v2 (epilog) information should be generated for x64
+/// Windows.
+ENUM_CODEGENOPT(WinX64EHUnwindV2, llvm::WinX64EHUnwindV2Mode,
+                2, llvm::WinX64EHUnwindV2Mode::Disabled)
 
 /// FIXME: Make DebugOptions its own top-level .def file.
 #include "DebugOptions.def"

clang/include/clang/Driver/Options.td

@@ -2167,11 +2167,14 @@ defm assume_nothrow_exception_dtor: BoolFOption<"assume-nothrow-exception-dtor",
   LangOpts<"AssumeNothrowExceptionDtor">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option], "Assume that exception objects' destructors are non-throwing">,
   NegFlag<SetFalse>>;
-defm winx64_eh_unwindv2 : BoolFOption<"winx64-eh-unwindv2",
-  CodeGenOpts<"WinX64EHUnwindV2">, DefaultFalse,
-  PosFlag<SetTrue, [], [ClangOption, CC1Option], "Enable">,
-  NegFlag<SetFalse, [], [ClangOption], "Disable">,
-  BothFlags<[], [ClangOption], " unwind v2 (epilog) information for x64 Windows">>;
+def winx64_eh_unwindv2
+    : Joined<["-"], "fwinx64-eh-unwindv2=">, Group<f_Group>,
+    Visibility<[ClangOption, CC1Option]>,
+      HelpText<"Generate unwind v2 (epilog) information for x64 Windows">,
+      Values<"disabled,best-effort,required">,
+      NormalizedValues<["Disabled", "BestEffort", "Required"]>,
+      NormalizedValuesScope<"llvm::WinX64EHUnwindV2Mode">,
+      MarshallingInfoEnum<CodeGenOpts<"WinX64EHUnwindV2">, "Disabled">;
 def fexcess_precision_EQ : Joined<["-"], "fexcess-precision=">, Group<f_Group>,
   Visibility<[ClangOption, CLOption]>,
   HelpText<"Allows control over excess precision on targets where native "
@@ -8971,7 +8974,9 @@ def _SLASH_volatile_Group : OptionGroup<"</volatile group>">,
   Group<cl_compile_Group>;
 
 def _SLASH_d2epilogunwind : CLFlag<"d2epilogunwind">,
-  HelpText<"Enable unwind v2 (epilog) information for x64 Windows">;
+  HelpText<"Best effort generate unwind v2 (epilog) information for x64 Windows">;
+def _SLASH_d2epilogunwindrequirev2 : CLFlag<"d2epilogunwindrequirev2">,
+  HelpText<"Require generation of unwind v2 (epilog) information for x64 Windows">;
 def _SLASH_EH : CLJoined<"EH">, HelpText<"Set exception handling model">;
 def _SLASH_EP : CLFlag<"EP">,
   HelpText<"Disable linemarker output and preprocess to stdout">;

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1314,8 +1314,10 @@ void CodeGenModule::Release() {
                               1);
 
   // Enable unwind v2 (epilog).
-  if (CodeGenOpts.WinX64EHUnwindV2)
-    getModule().addModuleFlag(llvm::Module::Warning, "winx64-eh-unwindv2", 1);
+  if (CodeGenOpts.getWinX64EHUnwindV2() != llvm::WinX64EHUnwindV2Mode::Disabled)
+    getModule().addModuleFlag(
+        llvm::Module::Warning, "winx64-eh-unwindv2",
+        static_cast<unsigned>(CodeGenOpts.getWinX64EHUnwindV2()));
 
   // Indicate whether this Module was compiled with -fopenmp
   if (getLangOpts().OpenMP && !getLangOpts().OpenMPSimd)

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7352,8 +7352,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   }
 
   // Unwind v2 (epilog) information for x64 Windows.
-  Args.addOptInFlag(CmdArgs, options::OPT_fwinx64_eh_unwindv2,
-                    options::OPT_fno_winx64_eh_unwindv2);
+  Args.AddLastArg(CmdArgs, options::OPT_winx64_eh_unwindv2);
 
   // C++ "sane" operator new.
   Args.addOptOutFlag(CmdArgs, options::OPT_fassume_sane_operator_new,
@@ -8410,8 +8409,10 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
     CmdArgs.push_back("-fms-kernel");
 
   // Unwind v2 (epilog) information for x64 Windows.
-  if (Args.hasArg(options::OPT__SLASH_d2epilogunwind))
-    CmdArgs.push_back("-fwinx64-eh-unwindv2");
+  if (Args.hasArg(options::OPT__SLASH_d2epilogunwindrequirev2))
+    CmdArgs.push_back("-fwinx64-eh-unwindv2=required");
+  else if (Args.hasArg(options::OPT__SLASH_d2epilogunwind))
+    CmdArgs.push_back("-fwinx64-eh-unwindv2=best-effort");
 
   for (const Arg *A : Args.filtered(options::OPT__SLASH_guard)) {
     StringRef GuardArgs = A->getValue();

clang/test/CodeGen/epilog-unwind.c

@@ -1,9 +1,11 @@
 // RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s -check-prefix=DISABLED
-// RUN: %clang_cc1 -fwinx64-eh-unwindv2 -emit-llvm %s -o - | FileCheck %s -check-prefix=ENABLED
-// RUN: %clang -fwinx64-eh-unwindv2 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=ENABLED
-// RUN: %clang -fno-winx64-eh-unwindv2 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=DISABLED
+// RUN: %clang_cc1 -fwinx64-eh-unwindv2=disabled -emit-llvm %s -o - | FileCheck %s -check-prefix=DISABLED
+// RUN: %clang_cc1 -fwinx64-eh-unwindv2=best-effort -emit-llvm %s -o - | FileCheck %s -check-prefix=BESTEFFORT
+// RUN: %clang_cc1 -fwinx64-eh-unwindv2=required -emit-llvm %s -o - | FileCheck %s -check-prefix=REQUIRED
+// RUN: %clang -fwinx64-eh-unwindv2=best-effort -S -emit-llvm %s -o - | FileCheck %s -check-prefix=BESTEFFORT
 
 void f(void) {}
 
-// ENABLED: !"winx64-eh-unwindv2", i32 1}
+// BESTEFFORT: !"winx64-eh-unwindv2", i32 1}
+// REQUIRED: !"winx64-eh-unwindv2", i32 2}
 // DISABLED-NOT: "winx64-eh-unwindv2"

clang/test/Driver/cl-options.c

@@ -821,7 +821,11 @@
 // ARM64EC_OVERRIDE: warning: /arm64EC has been overridden by specified target: x86_64-pc-windows-msvc; option ignored
 
 // RUN: %clang_cl /d2epilogunwind /c -### -- %s 2>&1 | FileCheck %s --check-prefix=EPILOGUNWIND
-// EPILOGUNWIND: -fwinx64-eh-unwindv2
+// EPILOGUNWIND: -fwinx64-eh-unwindv2=best-effort
+
+// RUN: %clang_cl /d2epilogunwindrequirev2 /c -### -- %s 2>&1 | FileCheck %s --check-prefix=EPILOGUNWINDREQUIREV2
+// RUN: %clang_cl /d2epilogunwindrequirev2 /d2epilogunwind /c -### -- %s 2>&1 | FileCheck %s --check-prefix=EPILOGUNWINDREQUIREV2
+// EPILOGUNWINDREQUIREV2: -fwinx64-eh-unwindv2=require
 
 // RUN: %clang_cl /funcoverride:override_me1 /funcoverride:override_me2 /c -### -- %s 2>&1 | FileCheck %s --check-prefix=FUNCOVERRIDE
 // FUNCOVERRIDE: -loader-replaceable-function=override_me1

llvm/include/llvm/IR/Module.h

@@ -1041,6 +1041,10 @@ class LLVM_ABI Module {
 
   /// Returns target-abi from MDString, null if target-abi is absent.
   StringRef getTargetABIFromMD();
+
+  /// Get how unwind v2 (epilog) information should be generated for x64
+  /// Windows.
+  WinX64EHUnwindV2Mode getWinX64EHUnwindV2Mode() const;
 };
 
 /// Given "llvm.used" or "llvm.compiler.used" as a global name, collect the

llvm/include/llvm/Support/CodeGen.h

@@ -130,6 +130,15 @@ namespace llvm {
     Invalid = 2, ///< Not used.
   };
 
+  enum class WinX64EHUnwindV2Mode {
+    // Don't use unwind v2 (i.e., use v1).
+    Disabled = 0,
+    // Use unwind v2 here possible, otherwise fallback to v1.
+    BestEffort = 1,
+    // Use unwind v2 everywhere, otherwise raise an error.
+    Required = 2,
+  };
+
   } // namespace llvm
 
 #endif

llvm/lib/IR/Module.cpp

@@ -917,3 +917,10 @@ StringRef Module::getTargetABIFromMD() {
     TargetABI = TargetABIMD->getString();
   return TargetABI;
 }
+
+WinX64EHUnwindV2Mode Module::getWinX64EHUnwindV2Mode() const {
+  Metadata *MD = getModuleFlag("winx64-eh-unwindv2");
+  if (auto *CI = mdconst::dyn_extract_or_null<ConstantInt>(MD))
+    return static_cast<WinX64EHUnwindV2Mode>(CI->getZExtValue());
+  return WinX64EHUnwindV2Mode::Disabled;
+}