[Driver] Disable uwtable by default in -ffreestanding mode

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

Differential Revision: https://reviews.llvm.org/D37777

llvm-svn: 313087

Author: vedantk

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3392,6 +3392,15 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     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.
@@ -3400,7 +3409,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                    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");
@@ -3790,11 +3799,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   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);

clang/test/Driver/clang-translation.c

@@ -73,6 +73,22 @@
 // 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