clang-cl: Disable TBAA by default for MSVC compatibility

MSVC doesn't have an option to enable TBAA, so make -fstrict-aliasing
and -fno-strict-aliasing available in clang-cl.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205924 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 16 insertions, 3 deletions

diff --git a/include/clang/Driver/Options.td b/include/clang/Driver/Options.td
index 33e058fde6..dd7055690c 100644
--- a/include/clang/Driver/Options.td
+++ b/include/clang/Driver/Options.td
@@ -687,7 +687,8 @@ def fno_spell_checking : Flag<["-"], "fno-spell-checking">, Group<f_Group>,
   Flags<[CC1Option]>, HelpText<"Disable spell-checking">;
 def fno_stack_protector : Flag<["-"], "fno-stack-protector">, Group<f_Group>,
   HelpText<"Disable the use of stack protectors">;
-def fno_strict_aliasing : Flag<["-"], "fno-strict-aliasing">, Group<f_Group>;
+def fno_strict_aliasing : Flag<["-"], "fno-strict-aliasing">, Group<f_Group>,
+  Flags<[DriverOption, CoreOption]>;
 def fstruct_path_tbaa : Flag<["-"], "fstruct-path-tbaa">, Group<f_Group>;
 def fno_struct_path_tbaa : Flag<["-"], "fno-struct-path-tbaa">, Group<f_Group>;
 def fno_strict_enums : Flag<["-"], "fno-strict-enums">, Group<f_Group>;
@@ -799,7 +800,8 @@ def fno_standalone_debug : Flag<["-"], "fno-standalone-debug">, Group<f_Group>,
   HelpText<"Limit debug information produced to reduce size of debug binary">;
 def flimit_debug_info : Flag<["-"], "flimit-debug-info">, Alias<fno_standalone_debug>;
 def fno_limit_debug_info : Flag<["-"], "fno-limit-debug-info">, Alias<fstandalone_debug>;
-def fstrict_aliasing : Flag<["-"], "fstrict-aliasing">, Group<f_Group>;
+def fstrict_aliasing : Flag<["-"], "fstrict-aliasing">, Group<f_Group>,
+  Flags<[DriverOption, CoreOption]>;
 def fstrict_enums : Flag<["-"], "fstrict-enums">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Enable optimizations based on the strict definition of an enum's "
            "value range">;
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index e65b6e1782..28702836de 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -2508,8 +2508,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // enabled.  This alias option is being used to simplify the hasFlag logic.
   OptSpecifier StrictAliasingAliasOption = OFastEnabled ? options::OPT_Ofast :
     options::OPT_fstrict_aliasing;
+  // We turn strict aliasing off by default if we're in CL mode, since MSVC
+  // doesn't do any TBAA.
+  bool TBAAOnByDefault = !getToolChain().getDriver().IsCLMode();
   if (!Args.hasFlag(options::OPT_fstrict_aliasing, StrictAliasingAliasOption,
-                    options::OPT_fno_strict_aliasing, true))
+                    options::OPT_fno_strict_aliasing, TBAAOnByDefault))
     CmdArgs.push_back("-relaxed-aliasing");
   if (!Args.hasFlag(options::OPT_fstruct_path_tbaa,
                     options::OPT_fno_struct_path_tbaa))
diff --git a/test/Driver/cl-options.c b/test/Driver/cl-options.c
index a76626464a..48f1a9e4af 100644
--- a/test/Driver/cl-options.c
+++ b/test/Driver/cl-options.c
@@ -133,6 +133,14 @@
 // WJoined: "-cc1"
 // WJoined: "-Wunused-pragmas"
 
+// We recognize -f[no-]strict-aliasing.
+// RUN: %clang_cl -c -### -- %s 2>&1 | FileCheck -check-prefix=DEFAULTSTRICT %s
+// DEFAULTSTRICT: "-relaxed-aliasing"
+// RUN: %clang_cl -c -fstrict-aliasing -### -- %s 2>&1 | FileCheck -check-prefix=STRICT %s
+// STRICT-NOT: "-relaxed-aliasing"
+// RUN: %clang_cl -c -fno-strict-aliasing -### -- %s 2>&1 | FileCheck -check-prefix=NOSTRICT %s
+// NOSTRICT: "-relaxed-aliasing"
+
 // For some warning ids, we can map from MSVC warning to Clang warning.
 // RUN: %clang_cl -wd4005 -### -- %s 2>&1 | FileCheck -check-prefix=wd4005 %s
 // wd4005: "-cc1"