[clang] [clang][driver] Add -mtls-dialect option (PR #79031)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Paul Kirth (ilovepi)

<details>
<summary>Changes</summary>

GCC an other ELF compilers support -mlts-dialect= options to control the
use of ELF TLS Descriptors as part of the TLS model. This patch only
adds support to the clang driver for the flag. Support for the
EnableTLSDesc code generation option in LLVM is added separately.


---
Full diff: https://github.com/llvm/llvm-project/pull/79031.diff


6 Files Affected:

- (modified) clang/include/clang/Basic/CodeGenOptions.def (+3) 
- (modified) clang/include/clang/Basic/CodeGenOptions.h (+5) 
- (modified) clang/include/clang/Driver/Options.td (+7) 
- (modified) clang/lib/CodeGen/BackendUtil.cpp (+2) 
- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+8) 
- (added) clang/test/Driver/tls-dialect.c (+15) 


``````````diff
diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
index 2c4fb6745bc172f..6b96764b215be24 100644
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -359,6 +359,9 @@ ENUM_CODEGENOPT(VecLib, llvm::driver::VectorLibrary, 3, llvm::driver::VectorLibr
 /// The default TLS model to use.
 ENUM_CODEGENOPT(DefaultTLSModel, TLSModel, 2, GeneralDynamicTLSModel)
 
+/// The default TLS model to use.
+ENUM_CODEGENOPT(DefaultTLSDialect, TLSDialect, 2, TraditionalTLSDialect)
+
 /// Bit size of immediate TLS offsets (0 == use the default).
 VALUE_CODEGENOPT(TLSSize, 8, 0)
 
diff --git a/clang/include/clang/Basic/CodeGenOptions.h b/clang/include/clang/Basic/CodeGenOptions.h
index 6952b48e898a819..23180ababa956f1 100644
--- a/clang/include/clang/Basic/CodeGenOptions.h
+++ b/clang/include/clang/Basic/CodeGenOptions.h
@@ -72,6 +72,11 @@ class CodeGenOptions : public CodeGenOptionsBase {
     LocalExecTLSModel
   };
 
+  enum TLSDialect {
+    TraditionalTLSDialect,
+    TLSDescTLSDialect,
+  };
+
   enum StructReturnConventionKind {
     SRCK_Default,  // No special option was passed.
     SRCK_OnStack,  // Small structs on the stack (-fpcc-struct-return).
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d2e6c3ff721c27e..e0923dc2b5469bf 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4403,6 +4403,13 @@ def mtls_size_EQ : Joined<["-"], "mtls-size=">, Group<m_Group>,
   HelpText<"Specify bit size of immediate TLS offsets (AArch64 ELF only): "
            "12 (for 4KB) | 24 (for 16MB, default) | 32 (for 4GB) | 48 (for 256TB, needs -mcmodel=large)">,
   MarshallingInfoInt<CodeGenOpts<"TLSSize">>;
+def mtls_dialect_EQ : Joined<["-"], "mtls-dialect=">, Group<m_Group>,
+  Visibility<[ClangOption, CC1Option]>,
+  HelpText<"Use the given thread-local storage dialect">,
+  Values<"trad,desc">,
+  NormalizedValuesScope<"CodeGenOptions">,
+  NormalizedValues<["TraditionalTLSDialect", "TLSDescTLSDialect"]>,
+  MarshallingInfoEnum<CodeGenOpts<"DefaultTLSDialect">, "TraditionalTLSDialect">;
 def mimplicit_it_EQ : Joined<["-"], "mimplicit-it=">, Group<m_Group>;
 def mdefault_build_attributes : Joined<["-"], "mdefault-build-attributes">, Group<m_Group>;
 def mno_default_build_attributes : Joined<["-"], "mno-default-build-attributes">, Group<m_Group>;
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index a6142d99f3b688d..0ab8156ab1f949b 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -401,6 +401,8 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
   Options.UniqueBasicBlockSectionNames =
       CodeGenOpts.UniqueBasicBlockSectionNames;
   Options.TLSSize = CodeGenOpts.TLSSize;
+  // TODO: Add correct codegen options in LLVM
+  // Options.TLSDesc = CodeGenOpts.getDefaultTLSDialect();
   Options.EmulatedTLS = CodeGenOpts.EmulatedTLS;
   Options.DebuggerTuning = CodeGenOpts.getDebuggerTuning();
   Options.EmitStackSizeSection = CodeGenOpts.StackSizeSection;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index fead2e884030e21..232b7c48d56b296 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5812,6 +5812,14 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     Args.AddLastArg(CmdArgs, options::OPT_mtls_size_EQ);
   }
 
+  if (Arg *A = Args.getLastArg(options::OPT_mtls_dialect_EQ)) {
+    // mlts-dialect= is ELF only
+    if (!Triple.isOSBinFormatELF())
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getOption().getName() << TripleStr;
+    Args.AddLastArg(CmdArgs, options::OPT_mtls_dialect_EQ);
+  }
+
   // Add the target cpu
   std::string CPU = getCPUName(D, Args, Triple, /*FromAs*/ false);
   if (!CPU.empty()) {
diff --git a/clang/test/Driver/tls-dialect.c b/clang/test/Driver/tls-dialect.c
new file mode 100644
index 000000000000000..42bf9ef42b0aa68
--- /dev/null
+++ b/clang/test/Driver/tls-dialect.c
@@ -0,0 +1,15 @@
+/// Options for ELF
+// RUN: %clang -### -target aarch64-linux-gnu -mtls-dialect=trad %s 2>&1 | FileCheck -check-prefix=TRAD %s
+// RUN: %clang -### -target aarch64-linux-gnu -mtls-dialect=desc %s 2>&1 | FileCheck -check-prefix=DESC %s
+
+/// Unsupported target
+// RUN: not %clang -target aarch64-unknown-windows-msvc -mtls-dialect=trad %s 2>&1 | FileCheck -check-prefix=UNSUPPORTED-TARGET %s
+// RUN: not %clang -target aarch64-unknown-windows-msvc -mtls-dialect=desc %s 2>&1 | FileCheck -check-prefix=UNSUPPORTED-TARGET %s
+
+/// Invalid option value
+// RUN: not %clang -target x86_64-linux-gnu -mtls-dialect=foo %s 2>&1 | FileCheck -check-prefix=INVALID-VALUE %s
+
+// TRAD: "-cc1" {{.*}}"-mtls-dialect=trad"
+// DESC: "-cc1" {{.*}}"-mtls-dialect=desc"
+// UNSUPPORTED-TARGET: error: unsupported option
+// INVALID-VALUE: error: invalid value 'foo' in '-mtls-dialect=foo'

``````````

</details>


https://github.com/llvm/llvm-project/pull/79031