[clang] Add /Zc:tlsGuards- option (PR #113830)

[Maurice Heumann via cfe-commits]

https://github.com/momo5502 created https://github.com/llvm/llvm-project/pull/113830

This fixes #103484

>From b1b4da14386856667d11c284535348002954f94f Mon Sep 17 00:00:00 2001
From: momo5502 <mauriceheumann at gmail.com>
Date: Sun, 27 Oct 2024 20:02:00 +0100
Subject: [PATCH] Add /Zc:tlsGuards- option

---
 clang/include/clang/Basic/LangOptions.def |  1 +
 clang/include/clang/Driver/Options.td     | 11 +++++++++++
 clang/lib/CodeGen/MicrosoftCXXABI.cpp     |  1 +
 clang/lib/Driver/ToolChains/Clang.cpp     |  4 ++++
 4 files changed, 17 insertions(+)

diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 68db400c22e6c1..bf2f23a2828176 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -186,6 +186,7 @@ COMPATIBLE_LANGOPT(RecoveryAST, 1, 1, "Preserve expressions in AST when encounte
 COMPATIBLE_LANGOPT(RecoveryASTType, 1, 1, "Preserve the type in recovery expressions")
 
 BENIGN_LANGOPT(ThreadsafeStatics , 1, 1, "thread-safe static initializers")
+BENIGN_LANGOPT(TlsGuards , 1, 1, "on-demand TLS initialization")
 LANGOPT(POSIXThreads      , 1, 0, "POSIX thread support")
 LANGOPT(Blocks            , 1, 0, "blocks extension to C")
 BENIGN_LANGOPT(EmitAllDecls      , 1, 0, "emitting all declarations")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 5df6ddd5e6a0c5..84b1404c214511 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4063,6 +4063,11 @@ defm threadsafe_statics : BoolFOption<"threadsafe-statics",
   NegFlag<SetFalse, [], [ClangOption, CC1Option],
           "Do not emit code to make initialization of local statics thread safe">,
   PosFlag<SetTrue>>;
+defm tls_guards : BoolFOption<"tls-guards",
+  LangOpts<"TlsGuards">, DefaultTrue,
+  NegFlag<SetFalse, [], [ClangOption, CC1Option],
+          "Do not emit code to perform on-demand initialization of thread-local variables">,
+  PosFlag<SetTrue>>;
 def ftime_report : Flag<["-"], "ftime-report">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option]>,
   MarshallingInfoFlag<CodeGenOpts<"TimePasses">>;
@@ -8610,6 +8615,12 @@ def _SLASH_Zc_threadSafeInit : CLFlag<"Zc:threadSafeInit">,
 def _SLASH_Zc_threadSafeInit_ : CLFlag<"Zc:threadSafeInit-">,
   HelpText<"Disable thread-safe initialization of static variables">,
   Alias<fno_threadsafe_statics>;
+def _SLASH_Zc_tlsGuards : CLFlag<"Zc:tlsGuards">,
+  HelpText<"Enable on-demand initialization of thread-local variables">,
+  Alias<ftls_guards>;
+def _SLASH_Zc_tlsGuards_ : CLFlag<"Zc:tlsGuards-">,
+  HelpText<"Disable on-demand initialization of thread-local variables">,
+  Alias<fno_tls_guards>;
 def _SLASH_Zc_trigraphs : CLFlag<"Zc:trigraphs">,
   HelpText<"Enable trigraphs">, Alias<ftrigraphs>;
 def _SLASH_Zc_trigraphs_off : CLFlag<"Zc:trigraphs-">,
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 0b0b45ffead92f..c705f3ad6e32ed 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -431,6 +431,7 @@ class MicrosoftCXXABI : public CGCXXABI {
   bool usesThreadWrapperFunction(const VarDecl *VD) const override {
     return getContext().getLangOpts().isCompatibleWithMSVC(
                LangOptions::MSVC2019_5) &&
+           getContext().getLangOpts().TlsGuards &&
            (!isEmittedWithConstantInitializer(VD) || mayNeedDestruction(VD));
   }
   LValue EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF, const VarDecl *VD,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 04b3832327a99c..da659fa4db235d 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -7291,6 +7291,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                         (!IsWindowsMSVC || IsMSVC2015Compatible)))
     CmdArgs.push_back("-fno-threadsafe-statics");
 
+  if (!Args.hasFlag(options::OPT_ftls_guards,
+                    options::OPT_fno_tls_guards, true))
+    CmdArgs.push_back("-fno-tls-guards");
+
   // Add -fno-assumptions, if it was specified.
   if (!Args.hasFlag(options::OPT_fassumptions, options::OPT_fno_assumptions,
                     true))