Add support for -mno-tls-direct-seg-refs to Clang

This patch exposes functionality added in rL344723 to the Clang driver/frontend
as a flag and adds appropriate metadata.

Driver tests pass:
```
ninja check-clang-driver
-snip-
  Expected Passes    : 472
  Expected Failures  : 3
  Unsupported Tests  : 65
```

Odd failure in CodeGen tests but unrelated to this:
```
ninja check-clang-codegen
-snip-
/SourceCache/llvm-trunk-8.0/tools/clang/test/CodeGen/builtins-wasm.c:87:10:
error: cannot compile this builtin function yet
-snip-
Failing Tests (1):
    Clang :: CodeGen/builtins-wasm.c

  Expected Passes    : 1250
  Expected Failures  : 2
  Unsupported Tests  : 120
  Unexpected Failures: 1
```

Original commit:
[X86] Support for the mno-tls-direct-seg-refs flag
Allows to disable direct TLS segment access (%fs or %gs). GCC supports a
similar flag, it can be useful in some circumstances, e.g. when a thread
context block needs to be updated directly from user space. More info and
specific use cases: https://bugs.llvm.org/show_bug.cgi?id=16145

Patch by nruslan (Ruslan Nikolaev).

Differential Revision: https://reviews.llvm.org/D53102

llvm-svn: 344739

clang/include/clang/Driver/Options.td

@@ -2011,6 +2011,8 @@ def mno_global_merge : Flag<["-"], "mno-global-merge">, Group<m_Group>, Flags<[C
 def mno_pascal_strings : Flag<["-"], "mno-pascal-strings">,
   Alias<fno_pascal_strings>;
 def mno_red_zone : Flag<["-"], "mno-red-zone">, Group<m_Group>;
+def mno_tls_direct_seg_refs : Flag<["-"], "mno-tls-direct-seg-refs">, Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"Disable direct TLS access through segment registers">;
 def mno_relax_all : Flag<["-"], "mno-relax-all">, Group<m_Group>;
 def mno_rtd: Flag<["-"], "mno-rtd">, Group<m_Group>;
 def mno_soft_float : Flag<["-"], "mno-soft-float">, Group<m_Group>;
@@ -2171,6 +2173,8 @@ def momit_leaf_frame_pointer : Flag<["-"], "momit-leaf-frame-pointer">, Group<m_
 def moslib_EQ : Joined<["-"], "moslib=">, Group<m_Group>;
 def mpascal_strings : Flag<["-"], "mpascal-strings">, Alias<fpascal_strings>;
 def mred_zone : Flag<["-"], "mred-zone">, Group<m_Group>;
+def mtls_direct_seg_refs : Flag<["-"], "mtls-direct-seg-refs">, Group<m_Group>,
+  HelpText<"Enable direct TLS access through segment registers (default)">;
 def mregparm_EQ : Joined<["-"], "mregparm=">, Group<m_Group>;
 def mrelax_all : Flag<["-"], "mrelax-all">, Group<m_Group>, Flags<[CC1Option,CC1AsOption]>,
   HelpText<"(integrated-as) Relax all machine instructions">;

clang/include/clang/Frontend/CodeGenOptions.def

@@ -62,6 +62,8 @@ CODEGENOPT(ExperimentalNewPassManager, 1, 0) ///< Enables the new, experimental
 CODEGENOPT(DebugPassManager, 1, 0) ///< Prints debug information for the new
                                    ///< pass manager.
 CODEGENOPT(DisableRedZone    , 1, 0) ///< Set when -mno-red-zone is enabled.
+CODEGENOPT(IndirectTlsSegRefs, 1, 0) ///< Set when -mno-tls-direct-seg-refs
+                                     ///< is specified.
 CODEGENOPT(DisableTailCalls  , 1, 0) ///< Do not emit tail calls.
 CODEGENOPT(NoEscapingBlockTailCalls, 1, 0) ///< Do not emit tail calls from
                                            ///< escaping blocks.

clang/lib/CodeGen/CGCall.cpp

@@ -1709,6 +1709,8 @@ void CodeGenModule::ConstructDefaultFnAttrList(StringRef Name, bool HasOptnone,
 
   if (CodeGenOpts.DisableRedZone)
     FuncAttrs.addAttribute(llvm::Attribute::NoRedZone);
+  if (CodeGenOpts.IndirectTlsSegRefs)
+    FuncAttrs.addAttribute("indirect-tls-seg-refs");
   if (CodeGenOpts.NoImplicitFloat)
     FuncAttrs.addAttribute(llvm::Attribute::NoImplicitFloat);
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1739,6 +1739,10 @@ void Clang::AddX86TargetArgs(const ArgList &Args,
       Args.hasArg(options::OPT_fapple_kext))
     CmdArgs.push_back("-disable-red-zone");
 
+  if (!Args.hasFlag(options::OPT_mtls_direct_seg_refs,
+                    options::OPT_mno_tls_direct_seg_refs, true))
+    CmdArgs.push_back("-mno-tls-direct-seg-refs");
+
   // Default to avoid implicit floating-point for kernel/kext code, but allow
   // that to be overridden with -mno-soft-float.
   bool NoImplicitFloat = (Args.hasArg(options::OPT_mkernel) ||

clang/lib/Frontend/CompilerInvocation.cpp

@@ -614,6 +614,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.DisableLifetimeMarkers = Args.hasArg(OPT_disable_lifetimemarkers);
   Opts.DisableO0ImplyOptNone = Args.hasArg(OPT_disable_O0_optnone);
   Opts.DisableRedZone = Args.hasArg(OPT_disable_red_zone);
+  Opts.IndirectTlsSegRefs = Args.hasArg(OPT_mno_tls_direct_seg_refs);
   Opts.ForbidGuardVariables = Args.hasArg(OPT_fforbid_guard_variables);
   Opts.UseRegisterSizedBitfieldAccess = Args.hasArg(
     OPT_fuse_register_sized_bitfield_access);

clang/test/CodeGen/indirect-tls-seg-refs.c

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - -mno-tls-direct-seg-refs | FileCheck %s -check-prefix=NO-TLSDIRECT
+// RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s -check-prefix=TLSDIRECT
+
+// NO-TLSDIRECT: attributes #{{[0-9]+}} = {{{.*}} "indirect-tls-seg-refs"
+// TLSDIRECT-NOT: attributes #{{[0-9]+}} = {{{.*}} "indirect-tls-seg-refs"
+
+void test1() {
+}

clang/test/Driver/indirect-tls-seg-refs.c

@@ -0,0 +1,7 @@
+// RUN: %clang -### %s 2>&1 | FileCheck %s -check-prefix=TLSDIRECT
+// RUN: %clang -### -mno-tls-direct-seg-refs -mtls-direct-seg-refs %s 2>&1 | FileCheck %s -check-prefix=TLSDIRECT
+// RUN: %clang -### -mtls-direct-seg-refs -mno-tls-direct-seg-refs %s 2>&1 | FileCheck %s -check-prefix=NO-TLSDIRECT
+// REQUIRES: clang-driver
+
+// NO-TLSDIRECT: -mno-tls-direct-seg-refs
+// TLSDIRECT-NOT: -mno-tls-direct-seg-refs