Recommit #2 "[Driver] Default to -fno-common for all targets"

After a first attempt to fix the test-suite failures, my first recommit
caused the same failures again. I had updated CMakeList.txt files of
tests that needed -fcommon, but it turns out that there are also
Makefiles which are used by some bots, so I've updated these Makefiles
now too.

See the original commit message for more details on this change:
0a9fc92

clang/docs/ClangCommandLineReference.rst

@@ -1307,6 +1307,10 @@ 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

@@ -84,6 +84,13 @@ 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

@@ -848,7 +848,8 @@ 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>;
+def fcommon : Flag<["-"], "fcommon">, Group<f_Group>,
+  Flags<[CoreOption, CC1Option]>, HelpText<"Place uninitialized global variables in a common block">;
 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

@@ -1408,20 +1408,6 @@ 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
@@ -5692,11 +5678,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (!Args.hasFlag(options::OPT_Qy, options::OPT_Qn, true))
     CmdArgs.push_back("-Qn");
 
-  // -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");
+  // -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");
 
   // -fsigned-bitfields is default, and clang doesn't yet support
   // -funsigned-bitfields.

clang/lib/Frontend/CompilerInvocation.cpp

@@ -811,7 +811,7 @@ 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_fno_common);
+  Opts.NoCommon = !Args.hasArg(OPT_fcommon);
   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 = common {{(dso_local )?}}global i32 0, align 4
-// CHECK: @g1 = common {{(dso_local )?}}global i32 0, align 4
+// CHECK: @g0 = {{(dso_local )?}}global i32 0, align 4
+// CHECK: @g1 = {{(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 = common global i32 0, align 4, !dbg [[G:![0-9]+]]
+// CHECK: @global = 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 = common global <vscale x 16 x i8>* null, align 8
+// CHECK: @ptr = 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 = common addrspace(1) global
+// CHECK: @foo = addrspace(1) global
 int foo __attribute__((address_space(1)));
 
-// CHECK: @ban = common addrspace(1) global
+// CHECK: @ban = addrspace(1) global
 int ban[10] __attribute__((address_space(1)));
 
-// CHECK: @a = common global
+// CHECK: @a = global
 int a __attribute__((address_space(0)));
 
 // CHECK-LABEL: define i32 @test1()

clang/test/CodeGen/alias.c

@@ -5,8 +5,13 @@
 // RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=CHECKGLOBALS %s
 
 int g0;
-// CHECKBASIC-DAG: @g0 = common global i32 0
-// CHECKASM-DAG: .comm g0,4,4
+// 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
 __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 = common global i8 0, align 2
+// CHECK-DAG: @c = global i8 0, align 2
 
 struct test s;
-// CHECK-DAG: @s = common global %struct.test zeroinitializer, align 2
+// CHECK-DAG: @s = 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 = common global [1024 x i64] zeroinitializer, align 8
+// CHECK-DAG: @test5 = 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 = common global i32 0
+// LINUX: @foo = global i32 0
 // LINUX: declare i8* @alias(i32)
 
 // DARWIN: @"\01bar" = internal global i32 0
-// DARWIN: @"\01foo" = common global i32 0
+// DARWIN: @"\01foo" = 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 = common global i32
+// CHECK: @C = 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 = common global i32 0, align 4
+// CHECK: @test2_f = 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 = common global i32 0, align 4
+// CHECK: @test4_f = 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 = common protected global i32 0
+// CHECK: @t6 = 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 = common dso_local dllexport global [5 x i32]
+// CHECK-BLOCKS-IN-BLOCKS-DEFN: @_NSConcreteStackBlock = 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 = common global %struct.teststruct1
+// CHECK-LABEL: @test1 = global %struct.teststruct1
 struct teststruct1 {_Bool a, b;} test1;
 
-// CHECK-LABEL: @test2 = common global i8* null
+// CHECK-LABEL: @test2 = global i8* null
 _Bool* test2;
 
-// CHECK-LABEL: @test3 = common global [10 x i8]
+// CHECK-LABEL: @test3 = global [10 x i8]
 _Bool test3[10];
 
-// CHECK-LABEL: @test4 = common global [0 x i8]* null
+// CHECK-LABEL: @test4 = 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 = common global %struct.ptr zeroinitializer
+// CHECK-DAG: @object = 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 = common global [32 x i64] zeroinitializer, align 16
-// CHECK-CF: @__CFConstantStringClassReference = common global [1 x i64] zeroinitializer, align 8
+// 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-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 = common dso_local dllexport global [32 x i32]
+// CHECK-CF-IN-CF-DEFN: @__CFConstantStringClassReference = 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 = common addrspace(1) global i32 0
+// CHECK-DAG: @foo = addrspace(1) global i32 0
 int foo;
 
-// CHECK-DAG: @ban = common addrspace(1) global [10 x i32] zeroinitializer
+// CHECK-DAG: @ban = addrspace(1) global [10 x i32] zeroinitializer
 int ban[10];
 
-// CHECK-DAG: @A = common addrspace(1) global i32* null
-// CHECK-DAG: @B = common addrspace(1) global i32* null
+// CHECK-DAG: @A = addrspace(1) global i32* null
+// CHECK-DAG: @B = 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 = common dso_local dllexport global i32 0, align 4
-// CHECK-LNX: @y = common global i32 0, align 4
+// CHECK-MSVC: @y = dso_local dllexport constant i32 0, align 4
+// CHECK-LNX: @y = constant 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 = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @GlobalDef = 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 = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @GlobalRedecl1 = dso_local dllexport global i32 0, align 4
 __declspec(dllexport) extern int GlobalRedecl1;
 __declspec(dllexport)        int GlobalRedecl1;
 
-// CHECK-DAG: @GlobalRedecl2 = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @GlobalRedecl2 = 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 = common dso_local dllexport global i32 0, align 4
-// CHECK-DAG: @PrecedenceGlobal1B = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal1A = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal1B = dso_local dllexport global i32 0, align 4
 __attribute__((dllimport, dllexport))       int PrecedenceGlobal1A;
 __declspec(dllimport) __declspec(dllexport) int PrecedenceGlobal1B;
 
-// CHECK-DAG: @PrecedenceGlobal2A = common dso_local dllexport global i32 0, align 4
-// CHECK-DAG: @PrecedenceGlobal2B = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal2A = dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobal2B = 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 = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobalRedecl2 = 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 = common dso_local dllexport global i32 0, align 4
+// CHECK-DAG: @PrecedenceGlobalMixed2 = 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 = common dso_local dllexport global i32
-// GNU: @GlobalRedecl4 = common dso_local global i32
+// MS: @GlobalRedecl4 = dso_local dllexport global i32
+// GNU: @GlobalRedecl4 = 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 -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -fcommon -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

@@ -1,15 +1,16 @@
 // 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-NOCOMMON
+// 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
 
-// CHECK-DEFAULT: @x = common {{(dso_local )?}}global
-// CHECK-NOCOMMON: @x = {{(dso_local )?}}global
+// CHECK-COMMON: @x = common {{(dso_local )?}}global
+// CHECK-DEFAULT: @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));