Revert "Recommit "[Driver] Default to -fno-common for all targets""

This reverts commit 2c36c23f3476baf3b9283ea387c579419a70b112.

Still problems in the test-suite, which I really thought I had fixed...

2 files changed, 20 insertions, 4 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 5b85a51..99faae3 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1408,6 +1408,20 @@ static bool isSignedCharDefault(const llvm::Triple &Triple) {
   }
 }
 
+static bool isNoCommonDefault(const llvm::Triple &Triple) {
+  switch (Triple.getArch()) {
+  default:
+    if (Triple.isOSFuchsia())
+      return true;
+    return false;
+
+  case llvm::Triple::xcore:
+  case llvm::Triple::wasm32:
+  case llvm::Triple::wasm64:
+    return true;
+  }
+}
+
 static bool hasMultipleInvocations(const llvm::Triple &Triple,
                                    const ArgList &Args) {
   // Supported only on Darwin where we invoke the compiler multiple times
@@ -5678,9 +5692,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (!Args.hasFlag(options::OPT_Qy, options::OPT_Qn, true))
     CmdArgs.push_back("-Qn");
 
-  // -fno-common is the default, set -fcommon only when that flag is set.
-  if (Args.hasFlag(options::OPT_fcommon, options::OPT_fno_common, false))
-    CmdArgs.push_back("-fcommon");
+  // -fcommon is the default unless compiling kernel code or the target says so
+  bool NoCommonDefault = KernelOrKext || isNoCommonDefault(RawTriple);
+  if (!Args.hasFlag(options::OPT_fcommon, options::OPT_fno_common,
+                    !NoCommonDefault))
+    CmdArgs.push_back("-fno-common");
 
   // -fsigned-bitfields is default, and clang doesn't yet support
   // -funsigned-bitfields.
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 6d5a23e..9f3522a 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -809,7 +809,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.RecordCommandLine =
       std::string(Args.getLastArgValue(OPT_record_command_line));
   Opts.MergeAllConstants = Args.hasArg(OPT_fmerge_all_constants);
-  Opts.NoCommon = !Args.hasArg(OPT_fcommon);
+  Opts.NoCommon = Args.hasArg(OPT_fno_common);
   Opts.NoInlineLineTables = Args.hasArg(OPT_gno_inline_line_tables);
   Opts.NoImplicitFloat = Args.hasArg(OPT_no_implicit_float);
   Opts.OptimizeSize = getOptimizationLevelSize(Args);