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

This reverts commit 2c36c23.

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

clang/docs/ClangCommandLineReference.rst

@@ -1307,10 +1307,6 @@ Use colors in diagnostics
 
 .. option:: -fcommon, -fno-common
 
-Place definitions of variables with no storage class and no initializer
-(tentative definitions) in a common block, instead of generating individual
-zero-initialized definitions (default -fno-common).
-
 .. option:: -fcompile-resource=<arg>, --resource <arg>, --resource=<arg>
 
 .. option:: -fconstant-cfstrings, -fno-constant-cfstrings

clang/docs/ReleaseNotes.rst

@@ -84,13 +84,6 @@ future versions of Clang.
 Modified Compiler Flags
 -----------------------
 
-- -fno-common has been enabled as the default for all targets.  Therefore, C
-  code that uses tentative definitions as definitions of a variable in multiple
-  translation units will trigger multiple-definition linker errors.  Generally,
-  this occurs when the use of the ``extern`` keyword is neglected in the declaration
-  of a variable in a header file. In some cases, no specific translation unit
-  provides a definition of the variable. The previous behavior can be restored by
-  specifying ``-fcommon``.
 
 New Pragmas in Clang
 --------------------

clang/include/clang/Driver/Options.td

@@ -848,8 +848,7 @@ def fno_record_command_line : Flag<["-"], "fno-record-command-line">,
   Group<f_clang_Group>;
 def : Flag<["-"], "frecord-gcc-switches">, Alias<frecord_command_line>;
 def : Flag<["-"], "fno-record-gcc-switches">, Alias<fno_record_command_line>;
-def fcommon : Flag<["-"], "fcommon">, Group<f_Group>,
-  Flags<[CoreOption, CC1Option]>, HelpText<"Place uninitialized global variables in a common block">;
+def fcommon : Flag<["-"], "fcommon">, Group<f_Group>;
 def fcompile_resource_EQ : Joined<["-"], "fcompile-resource=">, Group<f_Group>;
 def fcomplete_member_pointers : Flag<["-"], "fcomplete-member-pointers">, Group<f_clang_Group>,
    Flags<[CoreOption, CC1Option]>,

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.

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);

clang/test/CodeGen/2008-07-21-mixed-var-fn-decl.c

@@ -3,6 +3,6 @@
 int g0, f0();
 int f1(), g1;
 
-// CHECK: @g0 = {{(dso_local )?}}global i32 0, align 4
-// CHECK: @g1 = {{(dso_local )?}}global i32 0, align 4
+// CHECK: @g0 = common {{(dso_local )?}}global i32 0, align 4
+// CHECK: @g1 = common {{(dso_local )?}}global i32 0, align 4
 

clang/test/CodeGen/2009-10-20-GlobalDebug.c

@@ -2,10 +2,10 @@
 // RUN: %clang -target i386-apple-darwin10 -flto -S -g %s -o - | FileCheck %s
 
 // CHECK: @main.localstatic = internal global i32 0, align 4, !dbg [[L:![0-9]+]]
-// CHECK: @global = global i32 0, align 4, !dbg [[G:![0-9]+]]
+// CHECK: @global = common global i32 0, align 4, !dbg [[G:![0-9]+]]
 
 int global;
-int main() {
+int main() { 
   static int localstatic;
   return 0;
 }

clang/test/CodeGen/aarch64-sve.c

@@ -16,7 +16,7 @@
 // CHECK-DEBUG: cannot yet generate debug info for SVE type '__SVFloat64_t'
 // CHECK-DEBUG: cannot yet generate debug info for SVE type '__SVBool_t'
 
-// CHECK: @ptr = global <vscale x 16 x i8>* null, align 8
+// CHECK: @ptr = common global <vscale x 16 x i8>* null, align 8
 // CHECK: %s8 = alloca <vscale x 16 x i8>, align 16
 // CHECK: %s16 = alloca <vscale x 8 x i16>, align 16
 // CHECK: %s32 = alloca <vscale x 4 x i32>, align 16

clang/test/CodeGen/address-space.c

@@ -1,13 +1,13 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin -emit-llvm < %s | FileCheck -enable-var-scope -check-prefixes=CHECK,X86 %s
 // RUN: %clang_cc1 -triple amdgcn -emit-llvm < %s | FileCheck -enable-var-scope -check-prefixes=CHECK,AMDGCN %s
 
-// CHECK: @foo = addrspace(1) global
+// CHECK: @foo = common addrspace(1) global
 int foo __attribute__((address_space(1)));
 
-// CHECK: @ban = addrspace(1) global
+// CHECK: @ban = common addrspace(1) global
 int ban[10] __attribute__((address_space(1)));
 
-// CHECK: @a = global
+// CHECK: @a = common global
 int a __attribute__((address_space(0)));
 
 // CHECK-LABEL: define i32 @test1()

clang/test/CodeGen/alias.c

@@ -5,13 +5,8 @@
 // RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=CHECKGLOBALS %s
 
 int g0;
-// CHECKBASIC-DAG: @g0 = global i32 0
-// CHECKASM-DAG:  .bss
-// CHECKASM-DAG:  .globl  g0
-// CHECKASM-DAG:  .p2align  2
-// CHECKASM-DAG:  g0:
-// CHECKASM-DAG:  .long 0
-// CHECKASM-DAG:  .size g0, 4
+// CHECKBASIC-DAG: @g0 = common global i32 0
+// CHECKASM-DAG: .comm g0,4,4
 __thread int TL_WITH_ALIAS;
 // CHECKBASIC-DAG: @TL_WITH_ALIAS = thread_local global i32 0, align 4
 // CHECKASM-DAG: .globl TL_WITH_ALIAS

clang/test/CodeGen/align-systemz.c

@@ -7,10 +7,10 @@ struct test {
 };
 
 char c;
-// CHECK-DAG: @c = global i8 0, align 2
+// CHECK-DAG: @c = common global i8 0, align 2
 
 struct test s;
-// CHECK-DAG: @s = global %struct.test zeroinitializer, align 2
+// CHECK-DAG: @s = common global %struct.test zeroinitializer, align 2
 
 extern char ec;
 // CHECK-DAG: @ec = external global i8, align 2

clang/test/CodeGen/alignment.c

@@ -7,7 +7,7 @@ union {int a[4]; __attribute((aligned(16))) float b[4];} b;
 // CHECK: @b = {{.*}}zeroinitializer, align 16
 
 long long int test5[1024];
-// CHECK-DAG: @test5 = global [1024 x i64] zeroinitializer, align 8
+// CHECK-DAG: @test5 = common global [1024 x i64] zeroinitializer, align 8
 
 // PR5279 - Reduced alignment on typedef.
 typedef int myint __attribute__((aligned(1)));

clang/test/CodeGen/asm-label.c

@@ -11,9 +11,9 @@ int *test(void) {
 }
 
 // LINUX: @bar = internal global i32 0
-// LINUX: @foo = global i32 0
+// LINUX: @foo = common global i32 0
 // LINUX: declare i8* @alias(i32)
 
 // DARWIN: @"\01bar" = internal global i32 0
-// DARWIN: @"\01foo" = global i32 0
+// DARWIN: @"\01foo" = common global i32 0
 // DARWIN: declare i8* @"\01alias"(i32)

clang/test/CodeGen/attr-weak-import.c

@@ -20,7 +20,7 @@ extern int E __attribute__((weak_import));
 
 // CHECK: @A = global i32
 // CHECK-NOT: @B =
-// CHECK: @C = global i32
+// CHECK: @C = common global i32
 // CHECK: @D = global i32
 // CHECK: @E = global i32
 

clang/test/CodeGen/attr-weakref2.c

@@ -8,7 +8,7 @@ int test1_h(void) {
   return test1_g;
 }
 
-// CHECK: @test2_f = global i32 0, align 4
+// CHECK: @test2_f = common global i32 0, align 4
 int test2_f;
 static int test2_g __attribute__((weakref("test2_f")));
 int test2_h(void) {
@@ -25,7 +25,7 @@ int test3_h(void) {
   return test3_g;
 }
 
-// CHECK: @test4_f = global i32 0, align 4
+// CHECK: @test4_f = common global i32 0, align 4
 extern int test4_f;
 static int test4_g __attribute__((weakref("test4_f")));
 int test4_h(void) {

clang/test/CodeGen/attributes.c

@@ -20,7 +20,7 @@ int t18 = 1;
 // CHECK: @t16 = extern_weak global i32
 extern int t16 __attribute__((weak_import));
 
-// CHECK: @t6 = protected global i32 0
+// CHECK: @t6 = common protected global i32 0
 int t6 __attribute__((visibility("protected")));
 
 // CHECK: @t12 = global i32 0, section "SECT"

clang/test/CodeGen/blocks-windows.c

@@ -68,7 +68,7 @@ int (*g(void))(void) {
 }
 
 // CHECK-BLOCKS-IN-BLOCKS-DECL: @_NSConcreteStackBlock = external dso_local dllexport global i8*
-// CHECK-BLOCKS-IN-BLOCKS-DEFN: @_NSConcreteStackBlock = dso_local dllexport global [5 x i32]
+// CHECK-BLOCKS-IN-BLOCKS-DEFN: @_NSConcreteStackBlock = common dso_local dllexport global [5 x i32]
 // CHECK-BLOCKS-NOT-IN-BLOCKS: @_NSConcreteStackBlock = external dllimport global i8*
 // CHECK-BLOCKS-NOT-IN-BLOCKS-EXTERN: @_NSConcreteStackBlock = external dllimport global i8*
 // CHECK-BLOCKS-NOT-IN-BLOCKS-EXTERN-DLLIMPORT: @_NSConcreteStackBlock = external dllimport global i8*

clang/test/CodeGen/bool-convert.c

@@ -2,16 +2,16 @@
 // All of these should uses the memory representation of _Bool
 
 // CHECK-LABEL: %struct.teststruct1 = type { i8, i8 }
-// CHECK-LABEL: @test1 = global %struct.teststruct1
+// CHECK-LABEL: @test1 = common global %struct.teststruct1
 struct teststruct1 {_Bool a, b;} test1;
 
-// CHECK-LABEL: @test2 = global i8* null
+// CHECK-LABEL: @test2 = common global i8* null
 _Bool* test2;
 
-// CHECK-LABEL: @test3 = global [10 x i8]
+// CHECK-LABEL: @test3 = common global [10 x i8]
 _Bool test3[10];
 
-// CHECK-LABEL: @test4 = global [0 x i8]* null
+// CHECK-LABEL: @test4 = common global [0 x i8]* null
 _Bool (*test4)[];
 
 // CHECK-LABEL: define void @f(i32 %x)

clang/test/CodeGen/c11atomics.c

@@ -25,7 +25,7 @@ struct elem {
 // CHECK-DAG: %struct.elem = type { %struct.ptr }
 
 struct ptr object;
-// CHECK-DAG: @object = global %struct.ptr zeroinitializer
+// CHECK-DAG: @object = common global %struct.ptr zeroinitializer
 
 // CHECK-DAG: @testStructGlobal = global {{.*}} { i16 1, i16 2, i16 3, i16 4 }
 // CHECK-DAG: @testPromotedStructGlobal = global {{.*}} { %{{.*}} { i16 1, i16 2, i16 3 }, [2 x i8] zeroinitializer }

clang/test/CodeGen/cfstring-elf-cfbuild-x86_64.c

@@ -30,7 +30,7 @@ const CFStringRef string = (CFStringRef)__builtin___CFStringMakeConstantString("
 
 
 // CHECK-CF-IN-CF-DECL: @__CFConstantStringClassReference = external global [0 x i32]
-// CHECK-CF-IN-CF-DEFN: @__CFConstantStringClassReference = global [32 x i64] zeroinitializer, align 16
-// CHECK-CF: @__CFConstantStringClassReference = global [1 x i64] zeroinitializer, align 8
+// CHECK-CF-IN-CF-DEFN: @__CFConstantStringClassReference = common global [32 x i64] zeroinitializer, align 16
+// CHECK-CF: @__CFConstantStringClassReference = common global [1 x i64] zeroinitializer, align 8
 // CHECK-CF-EXTERN: @__CFConstantStringClassReference = external global [0 x i32]
 // CHECK-CF-EXTERN: @.str = private unnamed_addr constant [7 x i8] c"string\00", section ".rodata", align 1

clang/test/CodeGen/cfstring-windows.c

@@ -32,7 +32,7 @@ typedef struct __CFString *CFStringRef;
 const CFStringRef string = (CFStringRef)__builtin___CFStringMakeConstantString("string");
 
 // CHECK-CF-IN-CF-DECL: @__CFConstantStringClassReference = external dso_local dllexport global [0 x i32]
-// CHECK-CF-IN-CF-DEFN: @__CFConstantStringClassReference = dso_local dllexport global [32 x i32]
+// CHECK-CF-IN-CF-DEFN: @__CFConstantStringClassReference = common dso_local dllexport global [32 x i32]
 // CHECK-CF: @__CFConstantStringClassReference = external dllimport global [0 x i32]
 // CHECK-CF-EXTERN: @__CFConstantStringClassReference = external dllimport global [0 x i32]
 // CHECK-CF-EXTERN-DLLIMPORT: @__CFConstantStringClassReference = external dllimport global [0 x i32]

clang/test/CodeGen/default-address-space.c

@@ -1,13 +1,13 @@
 // RUN: %clang_cc1 -triple amdgcn---amdgiz -emit-llvm < %s | FileCheck -check-prefixes=CHECK,COM %s
 
-// CHECK-DAG: @foo = addrspace(1) global i32 0
+// CHECK-DAG: @foo = common addrspace(1) global i32 0
 int foo;
 
-// CHECK-DAG: @ban = addrspace(1) global [10 x i32] zeroinitializer
+// CHECK-DAG: @ban = common addrspace(1) global [10 x i32] zeroinitializer
 int ban[10];
 
-// CHECK-DAG: @A = addrspace(1) global i32* null
-// CHECK-DAG: @B = addrspace(1) global i32* null
+// CHECK-DAG: @A = common addrspace(1) global i32* null
+// CHECK-DAG: @B = common addrspace(1) global i32* null
 int *A;
 int *B;
 

clang/test/CodeGen/dllexport-1.c

@@ -9,8 +9,8 @@
 // CHECK-MSVC: @z = dso_local constant i32 4, align 4
 // CHECK-LNX: @z = constant i32 4, align 4
 
-// CHECK-MSVC: @y = dso_local dllexport constant i32 0, align 4
-// CHECK-LNX: @y = constant i32 0, align 4
+// CHECK-MSVC: @y = common dso_local dllexport global i32 0, align 4
+// CHECK-LNX: @y = common global i32 0, align 4
 
 __declspec(dllexport) int const x = 3;
 __declspec(dllexport) const int y;

clang/test/CodeGen/dllexport.c

@@ -14,7 +14,7 @@
 __declspec(dllexport) extern int ExternGlobalDecl;
 
 // dllexport implies a definition.
-// CHECK-DAG: @GlobalDef = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @GlobalDef = common dso_local dllexport global i32 0, align 4
 __declspec(dllexport) int GlobalDef;
 
 // Export definition.
@@ -27,11 +27,11 @@ __declspec(dllexport) extern int GlobalDeclInit;
 int GlobalDeclInit = 1;
 
 // Redeclarations
-// CHECK-DAG: @GlobalRedecl1 = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @GlobalRedecl1 = common dso_local dllexport global i32 0, align 4
 __declspec(dllexport) extern int GlobalRedecl1;
 __declspec(dllexport)        int GlobalRedecl1;
 
-// CHECK-DAG: @GlobalRedecl2 = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @GlobalRedecl2 = common dso_local dllexport global i32 0, align 4
 __declspec(dllexport) extern int GlobalRedecl2;
                              int GlobalRedecl2;
 
@@ -70,29 +70,29 @@ __declspec(dllexport) void redecl2(void);
 //===----------------------------------------------------------------------===//
 
 // dllexport takes precedence over the dllimport if both are specified.
-// CHECK-DAG: @PrecedenceGlobal1A = dso_local dllexport global i32 0, align 4
-// CHECK-DAG: @PrecedenceGlobal1B = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal1A = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal1B = common dso_local dllexport global i32 0, align 4
 __attribute__((dllimport, dllexport))       int PrecedenceGlobal1A;
 __declspec(dllimport) __declspec(dllexport) int PrecedenceGlobal1B;
 
-// CHECK-DAG: @PrecedenceGlobal2A = dso_local dllexport global i32 0, align 4
-// CHECK-DAG: @PrecedenceGlobal2B = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal2A = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal2B = common dso_local dllexport global i32 0, align 4
 __attribute__((dllexport, dllimport))       int PrecedenceGlobal2A;
 __declspec(dllexport) __declspec(dllimport) int PrecedenceGlobal2B;
 
 // CHECK-DAG: @PrecedenceGlobalRedecl1 = dso_local dllexport global i32 0, align 4
 __declspec(dllexport) extern int PrecedenceGlobalRedecl1;
 __declspec(dllimport)        int PrecedenceGlobalRedecl1 = 0;
 
-// CHECK-DAG: @PrecedenceGlobalRedecl2 = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobalRedecl2 = common dso_local dllexport global i32 0, align 4
 __declspec(dllimport) extern int PrecedenceGlobalRedecl2;
 __declspec(dllexport)        int PrecedenceGlobalRedecl2;
 
 // CHECK-DAG: @PrecedenceGlobalMixed1 = dso_local dllexport global i32 1, align 4
 __attribute__((dllexport)) extern int PrecedenceGlobalMixed1;
 __declspec(dllimport)             int PrecedenceGlobalMixed1 = 1;
 
-// CHECK-DAG: @PrecedenceGlobalMixed2 = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobalMixed2 = common dso_local dllexport global i32 0, align 4
 __attribute__((dllimport)) extern int PrecedenceGlobalMixed2;
 __declspec(dllexport)             int PrecedenceGlobalMixed2;
 

clang/test/CodeGen/dllimport.c

@@ -46,8 +46,8 @@ __declspec(dllimport) extern int GlobalRedecl3;
 USEVAR(GlobalRedecl3)
 
 // Make sure this works even if the decl has been used before it's defined (PR20792).
-// MS: @GlobalRedecl4 = dso_local dllexport global i32
-// GNU: @GlobalRedecl4 = dso_local global i32
+// MS: @GlobalRedecl4 = common dso_local dllexport global i32
+// GNU: @GlobalRedecl4 = common dso_local global i32
 __declspec(dllimport) extern int GlobalRedecl4;
 USEVAR(GlobalRedecl4)
                       int GlobalRedecl4; // dllimport ignored

clang/test/CodeGen/microsoft-no-common-align.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-windows-msvc -fcommon -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm -o - %s | FileCheck %s
 typedef float TooLargeAlignment __attribute__((__vector_size__(64)));
 typedef float NormalAlignment __attribute__((__vector_size__(4)));
 

clang/test/CodeGen/no-common.c

@@ -1,16 +1,15 @@
 // RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-DEFAULT
-// RUN: %clang_cc1 %s -fno-common -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-DEFAULT
-// RUN: %clang_cc1 %s -fcommon -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-COMMON
+// RUN: %clang_cc1 %s -fno-common -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-NOCOMMON
 
-// CHECK-COMMON: @x = common {{(dso_local )?}}global
-// CHECK-DEFAULT: @x = {{(dso_local )?}}global
+// CHECK-DEFAULT: @x = common {{(dso_local )?}}global
+// CHECK-NOCOMMON: @x = {{(dso_local )?}}global
 int x;
 
-// CHECK-COMMON: @ABC = {{(dso_local )?}}global
 // CHECK-DEFAULT: @ABC = {{(dso_local )?}}global
+// CHECK-NOCOMMON: @ABC = {{(dso_local )?}}global
 typedef void* (*fn_t)(long a, long b, char *f, int c);
 fn_t ABC __attribute__ ((nocommon));
 
-// CHECK-COMMON: @y = common {{(dso_local )?}}global
 // CHECK-DEFAULT: @y = common {{(dso_local )?}}global
+// CHECK-NOCOMMON: @y = common {{(dso_local )?}}global
 int y __attribute__((common));