[Driver] Disable uwtable by default in -ffreestanding mode

[vsk]

Summary

We make the same decision when compiling the kernel or kexts -- we
should do this in -ffreestanding mode as well to avoid size regressions
in a potentially large set of firmware projects.

It's still possible to get uwtable information in -ffreestanding mode by
compiling with -funwind-tables (I expect this to be a rare case: I
certainly haven't seen any projects like that).

Context: -munwind-tables was enabled by default for some arm targets in
r310006.

Testing: check-clang

rdar://problem/33934446

[ahatanak]

LGTM

cfe/trunk/lib/Driver/ToolChains/Clang.cpp

#endif
   }
 
   if (Args.hasFlag(options::OPT_mpie_copy_relocations,
                    options::OPT_mno_pie_copy_relocations,
                    false)) {
     CmdArgs.push_back("-mpie-copy-relocations");
   }
 
+  // -fhosted is default.
+  // TODO: Audit uses of KernelOrKext and see where it'd be more appropriate to
+  // use Freestanding.
+  bool Freestanding =
+      Args.hasFlag(options::OPT_ffreestanding, options::OPT_fhosted, false) ||
+      KernelOrKext;
+  if (Freestanding)
+    CmdArgs.push_back("-ffreestanding");
+
   // This is a coarse approximation of what llvm-gcc actually does, both
   // -fasynchronous-unwind-tables and -fnon-call-exceptions interact in more
   // complicated ways.
   bool AsynchronousUnwindTables =
       Args.hasFlag(options::OPT_fasynchronous_unwind_tables,
                    options::OPT_fno_asynchronous_unwind_tables,
                    (getToolChain().IsUnwindTablesDefault(Args) ||
                     getToolChain().getSanitizerArgs().needsUnwindTables()) &&
-                       !KernelOrKext);
+                       !Freestanding);
   if (Args.hasFlag(options::OPT_funwind_tables, options::OPT_fno_unwind_tables,
                    AsynchronousUnwindTables))
     CmdArgs.push_back("-munwind-tables");
 
   getToolChain().addClangTargetOptions(Args, CmdArgs,
                                        JA.getOffloadingDeviceKind());
 
   if (Arg *A = Args.getLastArg(options::OPT_flimited_precision_EQ)) {
if (A->getOption().matches(options::OPT_fvisibility_EQ)) {
       CmdArgs.push_back("default");
     }
   }
 
   Args.AddLastArg(CmdArgs, options::OPT_fvisibility_inlines_hidden);
 
   Args.AddLastArg(CmdArgs, options::OPT_ftlsmodel_EQ);
 
-  // -fhosted is default.
-  if (Args.hasFlag(options::OPT_ffreestanding, options::OPT_fhosted, false) ||
-      KernelOrKext)
-    CmdArgs.push_back("-ffreestanding");
-
   // Forward -f (flag) options which we can pass directly.
   Args.AddLastArg(CmdArgs, options::OPT_femit_all_decls);
   Args.AddLastArg(CmdArgs, options::OPT_fheinous_gnu_extensions);
   Args.AddLastArg(CmdArgs, options::OPT_fno_operator_names);
   // Emulated TLS is enabled by default on Android and OpenBSD, and can be enabled
   // manually with -femulated-tls.
   bool EmulatedTLSDefault = Triple.isAndroid() || Triple.isOSOpenBSD() ||
                             Triple.isWindowsCygwinEnvironment();

cfe/trunk/test/Driver/clang-translation.c

 // ARMV7_HARDFLOAT: "-mfloat-abi" "hard"
 // ARMV7_HARDFLOAT-NOT: "-msoft-float"
 // ARMV7_HARDFLOAT: "-x" "c"
 
 // RUN: %clang -target arm64-apple-ios10 -### -S %s -arch arm64 2>&1 | \
 // RUN: FileCheck -check-prefix=ARM64-APPLE %s
 // ARM64-APPLE: -munwind-table
 
+// RUN: %clang -target arm64-apple-ios10 -### -ffreestanding -S %s -arch arm64 2>&1 | \
+// RUN: FileCheck -check-prefix=ARM64-FREESTANDING-APPLE %s
+//
+// RUN: %clang -target arm64-apple-ios10 -### -fno-unwind-tables -ffreestanding -S %s -arch arm64 2>&1 | \
+// RUN: FileCheck -check-prefix=ARM64-FREESTANDING-APPLE %s
+//
+// ARM64-FREESTANDING-APPLE-NOT: -munwind-table
+
+// RUN: %clang -target arm64-apple-ios10 -### -funwind-tables -S %s -arch arm64 2>&1 | \
+// RUN: FileCheck -check-prefix=ARM64-EXPLICIT-UWTABLE-APPLE %s
+//
+// RUN: %clang -target arm64-apple-ios10 -### -ffreestanding -funwind-tables -S %s -arch arm64 2>&1 | \
+// RUN: FileCheck -check-prefix=ARM64-EXPLICIT-UWTABLE-APPLE %s
+//
+// ARM64-EXPLICIT-UWTABLE-APPLE: -munwind-table
+
 // RUN: %clang -target arm64-apple-ios10 -fno-exceptions -### -S %s -arch arm64 2>&1 | \
 // RUN: FileCheck -check-prefix=ARM64-APPLE-EXCEP %s
 // ARM64-APPLE-EXCEP-NOT: -munwind-table
 
 // RUN: %clang -target armv7k-apple-watchos4.0 -### -S %s -arch armv7k 2>&1 | \
 // RUN: FileCheck -check-prefix=ARMV7K-APPLE %s
 // ARMV7K-APPLE: -munwind-table