[clang] Explicitly set the EmulatedTLS codegen option

[mstorsjo]

Summary

Set the EmulatedTLS option based on Triple::hasDefaultEmulatedTLS()
if the user didn't specify it; set ExplicitEmulatedTLS to true
in llvm::TargetOptions and set EmulatedTLS to Clang's
opinion of what the default or preference is.

This avoids any risk of deviance between the two.

This affects one check of getCodeGenOpts().EmulatedTLS in
shouldAssumeDSOLocal in CodeGenModule, but as that check only
is done for TT.isWindowsGNUEnvironment(), and
hasDefaultEmulatedTLS() returns false for such environments
it doesn't make any current testable difference.

Some mingw distributions carry a downstream patch, that enables
emulated TLS by default for mingw targets in hasDefaultEmulatedTLS()

• and for such cases, this patch does make a difference and fixes the

detection of emulated TLS, if it is implicitly enabled.

This is an alternative to D132848.

[mstorsjo]

@efriedma Does this look like what you had in mind; does it seem reasonable to @aaron.ballman?

[aaron.ballman]

In D132916#3773791, @mstorsjo wrote:

@efriedma Does this look like what you had in mind; does it seem reasonable to @aaron.ballman?

This seems reasonable to me, but I leave it to @efriedma and @rjmccall for the final sign-off. This looks to be NFC, or have I missed something? (If it is NFC, you should add that to the title, and if it's not NFC, is there test coverage that can be added?)

[mstorsjo]

In D132916#3781108, @aaron.ballman wrote:

In D132916#3773791, @mstorsjo wrote:

@efriedma Does this look like what you had in mind; does it seem reasonable to @aaron.ballman?

This seems reasonable to me, but I leave it to @efriedma and @rjmccall for the final sign-off. This looks to be NFC, or have I missed something? (If it is NFC, you should add that to the title, and if it's not NFC, is there test coverage that can be added?)

There's no observable change in upstream llvm-project/clang, but it is a functional change for downstreams with other vendor patches applied. So I'm a bit undecided whether it should be marked that or not; you're certainly right about the point that a patch either is NFC or should have test changes though...

[efriedma]

LGTM

(I think you can call it "NFC" if there's no visible change in community; you don't have to try to account for downstream changes that might interact with it.)

clang/include/clang/Basic/CodeGenOptions.def

CODEGENOPT(EmitDeclMetadata  , 1, 0) ///< Emit special metadata indicating what
                                      ///< Decl* various IR entities came from.
                                      ///< Only useful when running CodeGen as a
                                      ///< subroutine.
 CODEGENOPT(EmitVersionIdentMetadata , 1, 1) ///< Emit compiler version metadata.
 CODEGENOPT(EmitGcovArcs      , 1, 0) ///< Emit coverage data files, aka. GCDA.
 CODEGENOPT(EmitGcovNotes     , 1, 0) ///< Emit coverage "notes" files, aka GCNO.
 CODEGENOPT(EmitOpenCLArgMetadata , 1, 0) ///< Emit OpenCL kernel arg metadata.
 CODEGENOPT(EmulatedTLS       , 1, 0) ///< Set by default or -f[no-]emulated-tls.
-CODEGENOPT(ExplicitEmulatedTLS , 1, 0) ///< Set if -f[no-]emulated-tls is used.
 /// Embed Bitcode mode (off/all/bitcode/marker).
 ENUM_CODEGENOPT(EmbedBitcode, EmbedBitcodeKind, 2, Embed_Off)
 /// Inline asm dialect, -masm=(att|intel)
 ENUM_CODEGENOPT(InlineAsmDialect, InlineAsmDialectKind, 1, IAD_ATT)
 CODEGENOPT(ForbidGuardVariables , 1, 0) ///< Issue errors if C++ guard variables
                                         ///< are required.
 CODEGENOPT(FunctionSections  , 1, 0) ///< Set when -ffunction-sections is enabled.
 CODEGENOPT(InstrumentFunctions , 1, 0) ///< Set when -finstrument-functions is

clang/lib/CodeGen/BackendUtil.cpp

static bool initTargetOptions(DiagnosticsEngine &Diags,
   Options.FunctionSections = CodeGenOpts.FunctionSections;
   Options.DataSections = CodeGenOpts.DataSections;
   Options.IgnoreXCOFFVisibility = LangOpts.IgnoreXCOFFVisibility;
   Options.UniqueSectionNames = CodeGenOpts.UniqueSectionNames;
   Options.UniqueBasicBlockSectionNames =
       CodeGenOpts.UniqueBasicBlockSectionNames;
   Options.TLSSize = CodeGenOpts.TLSSize;
   Options.EmulatedTLS = CodeGenOpts.EmulatedTLS;
-  Options.ExplicitEmulatedTLS = CodeGenOpts.ExplicitEmulatedTLS;
+  Options.ExplicitEmulatedTLS = true;
   Options.DebuggerTuning = CodeGenOpts.getDebuggerTuning();
   Options.EmitStackSizeSection = CodeGenOpts.StackSizeSection;
   Options.StackUsageOutput = CodeGenOpts.StackUsageOutput;
   Options.EmitAddrsig = CodeGenOpts.Addrsig;
   Options.ForceDwarfFrameSection = CodeGenOpts.ForceDwarfFrameSection;
   Options.EmitCallSiteInfo = CodeGenOpts.EmitCallSiteInfo;
   Options.EnableAIXExtendedAltivecABI = CodeGenOpts.EnableAIXExtendedAltivecABI;
   Options.XRayOmitFunctionIndex = CodeGenOpts.XRayOmitFunctionIndex;

clang/lib/Frontend/CompilerInvocation.cpp

#undef CODEGEN_OPTION_WITH_MARSHALLING
   for (const auto &F : Opts.LinkBitcodeFiles) {
     bool Builtint = F.LinkFlags == llvm::Linker::Flags::LinkOnlyNeeded &&
                     F.PropagateAttrs && F.Internalize;
     GenerateArg(Args,
                 Builtint ? OPT_mlink_builtin_bitcode : OPT_mlink_bitcode_file,
                 F.Filename, SA);
   }
 
-  // TODO: Consider removing marshalling annotations from f[no_]emulated_tls.
-  //  That would make it easy to generate the option only **once** if it was
-  //  explicitly set to non-default value.
-  if (Opts.ExplicitEmulatedTLS) {
-    GenerateArg(
-        Args, Opts.EmulatedTLS ? OPT_femulated_tls : OPT_fno_emulated_tls, SA);
-  }
 
   if (Opts.FPDenormalMode != llvm::DenormalMode::getIEEE())
     GenerateArg(Args, OPT_fdenormal_fp_math_EQ, Opts.FPDenormalMode.str(), SA);
 
   if ((Opts.FPDenormalMode != Opts.FP32DenormalMode) ||
       (Opts.FP32DenormalMode != llvm::DenormalMode::getIEEE()))
     GenerateArg(Args, OPT_fdenormal_fp_math_f32_EQ, Opts.FP32DenormalMode.str(),
                 SA);
if (A->getOption().matches(OPT_mlink_builtin_bitcode)) {
       // When linking CUDA bitcode, propagate function attributes so that
       // e.g. libdevice gets fast-math attrs if we're building with fast-math.
       F.PropagateAttrs = true;
       F.Internalize = true;
     }
     Opts.LinkBitcodeFiles.push_back(F);
   }
 
-  if (Args.getLastArg(OPT_femulated_tls) ||
-      Args.getLastArg(OPT_fno_emulated_tls)) {
-    Opts.ExplicitEmulatedTLS = true;
+  if (!Args.getLastArg(OPT_femulated_tls) &&
+      !Args.getLastArg(OPT_fno_emulated_tls)) {
+    Opts.EmulatedTLS = T.hasDefaultEmulatedTLS();
   }
 
   if (Arg *A = Args.getLastArg(OPT_ftlsmodel_EQ)) {
     if (T.isOSAIX()) {
       StringRef Name = A->getValue();
       if (Name != "global-dynamic")
         Diags.Report(diag::err_aix_unsupported_tls_model) << Name;
     }