diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
index 5af9d64ae0fc54..609e7fa66c00e7 100644
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/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
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 664ae4e4167c43..ce121ebe6055bb 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/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
 --------------------
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index bdcd771ff713b9..0d5cba8d682aea 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/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]>,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 5b85a5197f58f5..99faae396be3ba 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 6d5a23e95a55c2..9f3522a3e65453 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);
diff --git a/clang/test/CodeGen/2008-07-21-mixed-var-fn-decl.c b/clang/test/CodeGen/2008-07-21-mixed-var-fn-decl.c
index 89ec60282f8894..3c9591e2945e65 100644
--- a/clang/test/CodeGen/2008-07-21-mixed-var-fn-decl.c
+++ b/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
 
diff --git a/clang/test/CodeGen/2009-10-20-GlobalDebug.c b/clang/test/CodeGen/2009-10-20-GlobalDebug.c
index 14b83201363043..c8c247f6b041ec 100644
--- a/clang/test/CodeGen/2009-10-20-GlobalDebug.c
+++ b/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;
 }
diff --git a/clang/test/CodeGen/aarch64-sve.c b/clang/test/CodeGen/aarch64-sve.c
index 790b3a176182bd..bb4512d5ed93b0 100644
--- a/clang/test/CodeGen/aarch64-sve.c
+++ b/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
diff --git a/clang/test/CodeGen/address-space.c b/clang/test/CodeGen/address-space.c
index c66dfc87c0c00a..a76d2e743e6e67 100644
--- a/clang/test/CodeGen/address-space.c
+++ b/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()
diff --git a/clang/test/CodeGen/alias.c b/clang/test/CodeGen/alias.c
index 21483cfb950b09..f5bdf3c0587e8b 100644
--- a/clang/test/CodeGen/alias.c
+++ b/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
diff --git a/clang/test/CodeGen/align-systemz.c b/clang/test/CodeGen/align-systemz.c
index 9a6c2223832788..eaa1de64d34455 100644
--- a/clang/test/CodeGen/align-systemz.c
+++ b/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
diff --git a/clang/test/CodeGen/alignment.c b/clang/test/CodeGen/alignment.c
index ce0c58bee4bb3a..c9f58136e38a78 100644
--- a/clang/test/CodeGen/alignment.c
+++ b/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)));
diff --git a/clang/test/CodeGen/asm-label.c b/clang/test/CodeGen/asm-label.c
index 7c7383fa41fcf6..c06f11fd2d24d5 100644
--- a/clang/test/CodeGen/asm-label.c
+++ b/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)
diff --git a/clang/test/CodeGen/attr-weak-import.c b/clang/test/CodeGen/attr-weak-import.c
index f02d09e8150998..0707f59a608b9a 100644
--- a/clang/test/CodeGen/attr-weak-import.c
+++ b/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
 
diff --git a/clang/test/CodeGen/attr-weakref2.c b/clang/test/CodeGen/attr-weakref2.c
index 114f048a851832..99760635581d38 100644
--- a/clang/test/CodeGen/attr-weakref2.c
+++ b/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) {
diff --git a/clang/test/CodeGen/attributes.c b/clang/test/CodeGen/attributes.c
index f6323e9be5487c..4be38b6367dc70 100644
--- a/clang/test/CodeGen/attributes.c
+++ b/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"
diff --git a/clang/test/CodeGen/blocks-windows.c b/clang/test/CodeGen/blocks-windows.c
index 44e5f66525b266..2dd97ffdd2f3a9 100644
--- a/clang/test/CodeGen/blocks-windows.c
+++ b/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*
diff --git a/clang/test/CodeGen/bool-convert.c b/clang/test/CodeGen/bool-convert.c
index 745971446e612d..344fb6bb994a11 100644
--- a/clang/test/CodeGen/bool-convert.c
+++ b/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)
diff --git a/clang/test/CodeGen/c11atomics.c b/clang/test/CodeGen/c11atomics.c
index 0a32ebcc724e9f..cf251738be55e4 100644
--- a/clang/test/CodeGen/c11atomics.c
+++ b/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 }
diff --git a/clang/test/CodeGen/cfstring-elf-cfbuild-x86_64.c b/clang/test/CodeGen/cfstring-elf-cfbuild-x86_64.c
index e330624ead96e2..8b90d7c0c1d80f 100644
--- a/clang/test/CodeGen/cfstring-elf-cfbuild-x86_64.c
+++ b/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
diff --git a/clang/test/CodeGen/cfstring-windows.c b/clang/test/CodeGen/cfstring-windows.c
index 7c17f31d3dd4a8..fe7511eae141c4 100644
--- a/clang/test/CodeGen/cfstring-windows.c
+++ b/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]
diff --git a/clang/test/CodeGen/default-address-space.c b/clang/test/CodeGen/default-address-space.c
index 21ba2b3269c2c2..5450609e06bb8c 100644
--- a/clang/test/CodeGen/default-address-space.c
+++ b/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;
 
diff --git a/clang/test/CodeGen/dllexport-1.c b/clang/test/CodeGen/dllexport-1.c
index b24324b0a96ee4..5860591c83c79f 100644
--- a/clang/test/CodeGen/dllexport-1.c
+++ 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;
diff --git a/clang/test/CodeGen/dllexport.c b/clang/test/CodeGen/dllexport.c
index 4c1143cf5ca486..f27012ec2355cb 100644
--- a/clang/test/CodeGen/dllexport.c
+++ b/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;
 
@@ -70,13 +70,13 @@ __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;
 
@@ -84,7 +84,7 @@ __declspec(dllexport) __declspec(dllimport) int PrecedenceGlobal2B;
 __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;
 
@@ -92,7 +92,7 @@ __declspec(dllexport)        int PrecedenceGlobalRedecl2;
 __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;
 
diff --git a/clang/test/CodeGen/dllimport.c b/clang/test/CodeGen/dllimport.c
index 8a67716fd9cf0d..319770232a2899 100644
--- a/clang/test/CodeGen/dllimport.c
+++ b/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
diff --git a/clang/test/CodeGen/microsoft-no-common-align.c b/clang/test/CodeGen/microsoft-no-common-align.c
index 7b7d91037fe4c9..a7a27a062704fa 100644
--- a/clang/test/CodeGen/microsoft-no-common-align.c
+++ b/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)));
 
diff --git a/clang/test/CodeGen/no-common.c b/clang/test/CodeGen/no-common.c
index 11de0f23396e2d..f3a6a334e6f513 100644
--- a/clang/test/CodeGen/no-common.c
+++ b/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));
diff --git a/clang/test/CodeGen/pr25786.c b/clang/test/CodeGen/pr25786.c
index d24ab1ba41eb44..612da7e8a3690f 100644
--- a/clang/test/CodeGen/pr25786.c
+++ b/clang/test/CodeGen/pr25786.c
@@ -4,8 +4,8 @@
 void (__attribute__((regparm(3), stdcall)) *pf) ();
 void (__attribute__((regparm(2), stdcall)) foo)(int a) {
 }
-// CHECK: @pf = global void (...)* null
+// CHECK: @pf = common global void (...)* null
 // CHECK: define void @foo(i32 %a)
 
-// CHECK-OK: @pf = global void (...)* null
+// CHECK-OK: @pf = common global void (...)* null
 // CHECK-OK: define x86_stdcallcc void @foo(i32 inreg %a)
diff --git a/clang/test/CodeGen/pragma-pack-1.c b/clang/test/CodeGen/pragma-pack-1.c
index 3a9e391c4ef39f..773318c79f7c9a 100644
--- a/clang/test/CodeGen/pragma-pack-1.c
+++ b/clang/test/CodeGen/pragma-pack-1.c
@@ -64,5 +64,5 @@ struct S4
 // CHECK: %struct.S4 = type { [3 x i8], %struct.T4, i32 }
 // CHECK: %struct.T4 = type <{ i8, i32 }>
 
-// CHECK: @refs = global [[struct_ref]]
-// CHECK: @ss = global [[struct_S]]
+// CHECK: @refs = common global [[struct_ref]]
+// CHECK: @ss = common global [[struct_S]]
diff --git a/clang/test/CodeGen/pragma-weak.c b/clang/test/CodeGen/pragma-weak.c
index 28354dc031c6bf..d1f7ab6c3ebeee 100644
--- a/clang/test/CodeGen/pragma-weak.c
+++ b/clang/test/CodeGen/pragma-weak.c
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -emit-llvm %s -o - -verify | FileCheck %s
 
 // CHECK: @weakvar = weak global
-// CHECK: @__weakvar_alias = global
+// CHECK: @__weakvar_alias = common global
 // CHECK: @correct_linkage = weak global
 
 
diff --git a/clang/test/CodeGen/private-extern-redef.c b/clang/test/CodeGen/private-extern-redef.c
index e0d51b67e22810..580ce9bd4a089c 100644
--- a/clang/test/CodeGen/private-extern-redef.c
+++ b/clang/test/CodeGen/private-extern-redef.c
@@ -34,6 +34,6 @@ void foo() {
 // CHECK: @M = hidden global
 // CHECK: @O = hidden global
 // CHECK: @I = external hidden
-// CHECK: @N = hidden global
+// CHECK: @N = common hidden global
 // CHECK-NOT: @P
 
diff --git a/clang/test/CodeGen/tentative-decls.c b/clang/test/CodeGen/tentative-decls.c
index e24c3fcee740e5..32177872058718 100644
--- a/clang/test/CodeGen/tentative-decls.c
+++ b/clang/test/CodeGen/tentative-decls.c
@@ -1,16 +1,16 @@
 // RUN: %clang_cc1 -emit-llvm -w -o - %s | FileCheck %s
 
-// CHECK-DAG: @r = {{(dso_local )?}}global [1 x {{.*}}] zeroinitializer
+// CHECK-DAG: @r = common {{(dso_local )?}}global [1 x {{.*}}] zeroinitializer
 
 int r[];
 int (*a)[] = &r;
 
 struct s0;
 struct s0 x;
-// CHECK-DAG: @x = {{(dso_local )?}}global %struct.s0 zeroinitializer
+// CHECK-DAG: @x = common {{(dso_local )?}}global %struct.s0 zeroinitializer
 
 struct s0 y;
-// CHECK-DAG: @y = {{(dso_local )?}}global %struct.s0 zeroinitializer
+// CHECK-DAG: @y = common {{(dso_local )?}}global %struct.s0 zeroinitializer
 struct s0 *f0() {
   return &y;
 }
@@ -19,14 +19,14 @@ struct s0 {
   int x;
 };
 
-// CHECK-DAG: @b = {{(dso_local )?}}global [1 x {{.*}}] zeroinitializer
+// CHECK-DAG: @b = common {{(dso_local )?}}global [1 x {{.*}}] zeroinitializer
 int b[];
 int *f1() {
   return b;
 }
 
 // Check that the most recent tentative definition wins.
-// CHECK-DAG: @c = {{(dso_local )?}}global [4 x {{.*}}] zeroinitializer
+// CHECK-DAG: @c = common {{(dso_local )?}}global [4 x {{.*}}] zeroinitializer
 int c[];
 int c[4];
 
diff --git a/clang/test/CodeGen/tls-model.c b/clang/test/CodeGen/tls-model.c
index 313c3b1dfd41e6..41c8de0b0e893a 100644
--- a/clang/test/CodeGen/tls-model.c
+++ b/clang/test/CodeGen/tls-model.c
@@ -21,24 +21,24 @@ int __thread __attribute__((tls_model("initial-exec"))) z;
 
 // CHECK-GD: @z1 = global i32 0
 // CHECK-GD: @f.y = internal thread_local global i32 0
-// CHECK-GD: @z2 = global i32 0
+// CHECK-GD: @z2 = common global i32 0
 // CHECK-GD: @x = thread_local global i32 0
 // CHECK-GD: @z = thread_local(initialexec) global i32 0
 
 // CHECK-LD: @z1 = global i32 0
 // CHECK-LD: @f.y = internal thread_local(localdynamic) global i32 0
-// CHECK-LD: @z2 = global i32 0
+// CHECK-LD: @z2 = common global i32 0
 // CHECK-LD: @x = thread_local(localdynamic) global i32 0
 // CHECK-LD: @z = thread_local(initialexec) global i32 0
 
 // CHECK-IE: @z1 = global i32 0
 // CHECK-IE: @f.y = internal thread_local(initialexec) global i32 0
-// CHECK-IE: @z2 = global i32 0
+// CHECK-IE: @z2 = common global i32 0
 // CHECK-IE: @x = thread_local(initialexec) global i32 0
 // CHECK-IE: @z = thread_local(initialexec) global i32 0
 
 // CHECK-LE: @z1 = global i32 0
 // CHECK-LE: @f.y = internal thread_local(localexec) global i32 0
-// CHECK-LE: @z2 = global i32 0
+// CHECK-LE: @z2 = common global i32 0
 // CHECK-LE: @x = thread_local(localexec) global i32 0
 // CHECK-LE: @z = thread_local(initialexec) global i32 0
diff --git a/clang/test/CodeGen/visibility.c b/clang/test/CodeGen/visibility.c
index f5606a508a1e39..8e153b893a3fd2 100644
--- a/clang/test/CodeGen/visibility.c
+++ b/clang/test/CodeGen/visibility.c
@@ -3,15 +3,15 @@
 // RUN: %clang_cc1 %s -triple i386-unknown-unknown -fvisibility hidden -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-HIDDEN
 
 // CHECK-DEFAULT: @g_def = global i32 0
-// CHECK-DEFAULT: @g_com = global i32 0
+// CHECK-DEFAULT: @g_com = common global i32 0
 // CHECK-DEFAULT: @g_ext = external global i32
 // CHECK-DEFAULT: @g_deferred = internal global
 // CHECK-PROTECTED: @g_def = protected global i32 0
-// CHECK-PROTECTED: @g_com = protected global i32 0
+// CHECK-PROTECTED: @g_com = common protected global i32 0
 // CHECK-PROTECTED: @g_ext = external global i32
 // CHECK-PROTECTED: @g_deferred = internal global
 // CHECK-HIDDEN: @g_def = hidden global i32 0
-// CHECK-HIDDEN: @g_com = hidden global i32 0
+// CHECK-HIDDEN: @g_com = common hidden global i32 0
 // CHECK-HIDDEN: @g_ext = external global i32
 // CHECK-HIDDEN: @g_deferred = internal global
 int g_com;
diff --git a/clang/test/CodeGen/vlt_to_pointer.c b/clang/test/CodeGen/vlt_to_pointer.c
index 12aaaa9a1df383..22c620aa642984 100644
--- a/clang/test/CodeGen/vlt_to_pointer.c
+++ b/clang/test/CodeGen/vlt_to_pointer.c
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s
 
 int c[1][3*2];
-// CHECK: @{{.+}} = global [1 x [6 x {{i[0-9]+}}]] zeroinitializer
+// CHECK: @{{.+}} = {{.*}} global [1 x [6 x {{i[0-9]+}}]] zeroinitializer
 
 // CHECK-LABEL: @f
 int f(int * const m, int (**v)[*m * 2])
diff --git a/clang/test/CodeGen/volatile-1.c b/clang/test/CodeGen/volatile-1.c
index a0c7093363d702..c62a8fd4cd3d82 100644
--- a/clang/test/CodeGen/volatile-1.c
+++ b/clang/test/CodeGen/volatile-1.c
@@ -1,10 +1,10 @@
 // RUN: %clang_cc1 -Wno-return-type -Wno-unused-value -emit-llvm %s -w -o - | FileCheck %s
 
-// CHECK: @i = {{(dso_local )?}}global [[INT:i[0-9]+]] 0
+// CHECK: @i = common {{(dso_local )?}}global [[INT:i[0-9]+]] 0
 volatile int i, j, k;
 volatile int ar[5];
 volatile char c;
-// CHECK: @ci = {{(dso_local )?}}global [[CINT:.*]] zeroinitializer
+// CHECK: @ci = common {{(dso_local )?}}global [[CINT:.*]] zeroinitializer
 volatile _Complex int ci;
 volatile struct S {
 #ifdef __cplusplus
diff --git a/clang/test/CodeGen/weak-global.c b/clang/test/CodeGen/weak-global.c
new file mode 100644
index 00000000000000..f972cea912005b
--- /dev/null
+++ b/clang/test/CodeGen/weak-global.c
@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -emit-llvm < %s | grep common
+
+int i;
diff --git a/clang/test/CodeGen/windows-on-arm-dllimport-dllexport.c b/clang/test/CodeGen/windows-on-arm-dllimport-dllexport.c
index f2c5ff94ffae60..a2ebbf195f79ec 100644
--- a/clang/test/CodeGen/windows-on-arm-dllimport-dllexport.c
+++ b/clang/test/CodeGen/windows-on-arm-dllimport-dllexport.c
@@ -17,7 +17,7 @@ void call_imported_function() {
 }
 
 // CHECK: @import_int = external dllimport global i32
-// CHECK: @export_int = dso_local dllexport global i32 0, align 4
+// CHECK: @export_int = common dso_local dllexport global i32 0, align 4
 
 // CHECK: define dso_local dllexport arm_aapcs_vfpcc void @export_implemented_function()
 
diff --git a/clang/test/CodeGenCXX/clang-sections-tentative.c b/clang/test/CodeGenCXX/clang-sections-tentative.c
index 2e3d3410bd3681..e663079b9aa412 100644
--- a/clang/test/CodeGenCXX/clang-sections-tentative.c
+++ b/clang/test/CodeGenCXX/clang-sections-tentative.c
@@ -30,7 +30,7 @@ const int cy; // .rodata.2
 
 // CHECK: @x = global i32 0, align 4 #0
 // CHECK: @y = global i32 0, align 4 #1
-// CHECK: @z = global i32 0, align 4
+// CHECK: @z = common global i32 0, align 4
 // CHECK: @cx = constant i32 0, align 4 #2
 // CHECK: @cy = constant i32 0, align 4 #3
 // CHECK: @cz = constant i32 0, align 4 #1
diff --git a/clang/test/CodeGenObjC/constant-string-class.m b/clang/test/CodeGenObjC/constant-string-class.m
index 47184050056b32..adad6b012623a6 100644
--- a/clang/test/CodeGenObjC/constant-string-class.m
+++ b/clang/test/CodeGenObjC/constant-string-class.m
@@ -30,6 +30,6 @@ int main () {
   return 0;
 }
 
-// CHECK-FRAGILE: @_FooClassReference = global
+// CHECK-FRAGILE: @_FooClassReference = common global
 // CHECK-NONFRAGILE: @"OBJC_CLASS_$_Object" = external global
 // CHECK-NONFRAGILE: "OBJC_CLASS_$_Foo" = global
diff --git a/clang/test/CodeGenObjC/tentative-cfconstantstring.m b/clang/test/CodeGenObjC/tentative-cfconstantstring.m
index 978bcba6122b56..bb76b033cf5fab 100644
--- a/clang/test/CodeGenObjC/tentative-cfconstantstring.m
+++ b/clang/test/CodeGenObjC/tentative-cfconstantstring.m
@@ -31,7 +31,7 @@ -(void)someMethod {
 }
 @end
 
-// CHECK: @__CFConstantStringClassReference = global [24 x i32] zeroinitializer, align 16
+// CHECK: @__CFConstantStringClassReference = common global [24 x i32] zeroinitializer, align 16
 // CHECK: @_unnamed_cfstring_{{.*}} = private global %struct.__NSConstantString_tag { i32* getelementptr inbounds ([24 x i32], [24 x i32]* @__CFConstantStringClassReference, i32 0, i32 0)
 
 // CHECK-LABEL: define internal void @_inlineFunction()
diff --git a/clang/test/CodeGenOpenCL/address-spaces.cl b/clang/test/CodeGenOpenCL/address-spaces.cl
index 144466a690b3f8..3c8fea2a80bc50 100644
--- a/clang/test/CodeGenOpenCL/address-spaces.cl
+++ b/clang/test/CodeGenOpenCL/address-spaces.cl
@@ -53,10 +53,10 @@ void fc(constant int *arg) {}
 
 #ifdef CL20
 int i;
-// CL20-DAG: @i = {{(dso_local )?}}addrspace(1) global i32 0
+// CL20-DAG: @i = common {{(dso_local )?}}addrspace(1) global i32 0
 int *ptr;
 // CL20SPIR-DAG: @ptr = {{(common )?}}{{(dso_local )?}}addrspace(1) global i32 addrspace(4)* null
-// CL20AMDGCN-DAG: @ptr = {{(dso_local )?}}addrspace(1) global i32* null
+// CL20AMDGCN-DAG: @ptr = common {{(dso_local )?}}addrspace(1) global i32* null
 #endif
 
 // SPIR: i32* %arg
diff --git a/clang/test/CodeGenOpenCL/amdgcn-large-globals.cl b/clang/test/CodeGenOpenCL/amdgcn-large-globals.cl
index cf7db165f46b6a..ea9ea618a48895 100644
--- a/clang/test/CodeGenOpenCL/amdgcn-large-globals.cl
+++ b/clang/test/CodeGenOpenCL/amdgcn-large-globals.cl
@@ -1,11 +1,11 @@
 // REQUIRES: amdgpu-registered-target
 // RUN: %clang_cc1 -cl-std=CL2.0 -triple amdgcn-unknown-unknown -S -emit-llvm -o - %s | FileCheck %s
 
-// CHECK: @One = local_unnamed_addr addrspace(1) global [6442450944 x i8] zeroinitializer, align 1
+// CHECK: @One = common local_unnamed_addr addrspace(1) global [6442450944 x i8] zeroinitializer, align 1
 unsigned char One[6442450944];
-// CHECK: @Two = local_unnamed_addr addrspace(1) global [6442450944 x i32] zeroinitializer, align 4
+// CHECK: @Two = common local_unnamed_addr addrspace(1) global [6442450944 x i32] zeroinitializer, align 4
 global unsigned int Two[6442450944];
-
+ 
 kernel void large_globals(unsigned int id) {
   One[id] = id;
   Two[id + 1] = id + 1;
diff --git a/clang/test/CodeGenOpenCL/amdgpu-nullptr.cl b/clang/test/CodeGenOpenCL/amdgpu-nullptr.cl
index ba34d168bf7905..c7c77920b7756c 100644
--- a/clang/test/CodeGenOpenCL/amdgpu-nullptr.cl
+++ b/clang/test/CodeGenOpenCL/amdgpu-nullptr.cl
@@ -1,7 +1,6 @@
 // RUN: %clang_cc1 %s -cl-std=CL2.0 -include opencl-c.h -triple amdgcn -emit-llvm -o - | FileCheck %s
 // RUN: %clang_cc1 %s -O0 -cl-std=CL2.0 -include opencl-c.h -triple amdgcn -emit-llvm -o - | FileCheck --check-prefix=NOOPT %s
 // RUN: %clang_cc1 %s -cl-std=CL2.0 -include opencl-c.h -triple amdgcn---opencl -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s -cl-std=CL2.0 -include opencl-c.h -triple amdgcn -fcommon -emit-llvm -o - | FileCheck %s --check-prefix=COMMON
 
 typedef struct {
   private char *p1;
@@ -17,6 +16,9 @@ typedef struct {
   generic char *p5;
 } StructTy2;
 
+// LLVM requests global variable with common linkage to be initialized with zeroinitializer, therefore use -fno-common
+// to suppress common linkage for tentative definition.
+
 // Test 0 as initializer.
 
 // CHECK: @private_p = local_unnamed_addr addrspace(1) global i8 addrspace(5)* null, align 4
@@ -181,39 +183,34 @@ void test_func_scope_var_local(void) {
 // cannot have common linkage since common linkage requires zero initialization
 // and does not have explicit section.
 
-// CHECK: @p1 = local_unnamed_addr addrspace(1) global i8 addrspace(5)* null, align 4
-// COMMON: @p1 = common local_unnamed_addr addrspace(1) global i8 addrspace(5)* null, align 4
+// CHECK: @p1 = common local_unnamed_addr addrspace(1) global i8 addrspace(5)* null, align 4
 private char *p1;
 
-// CHECK: @p2 = local_unnamed_addr addrspace(1) global i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), align 4
-// COMMON: @p2 = weak local_unnamed_addr addrspace(1) global i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), align 4
+// CHECK: @p2 = weak local_unnamed_addr addrspace(1) global i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), align 4
 local char *p2;
 
-// CHECK: @p3 = local_unnamed_addr addrspace(1) global i8 addrspace(4)* null, align 8
-// COMMON: @p3 = common local_unnamed_addr addrspace(1) global i8 addrspace(4)* null, align 8
+// CHECK: @p3 = common local_unnamed_addr addrspace(1) global i8 addrspace(4)* null, align 8
 constant char *p3;
 
-// CHECK: @p4 = local_unnamed_addr addrspace(1) global i8 addrspace(1)* null, align 8
-// COMMON: @p4 = common local_unnamed_addr addrspace(1) global i8 addrspace(1)* null, align 8
+// CHECK: @p4 = common local_unnamed_addr addrspace(1) global i8 addrspace(1)* null, align 8
 global char *p4;
 
-// CHECK: @p5 = local_unnamed_addr addrspace(1) global i8* null, align 8
-// COMMON: @p5 = common local_unnamed_addr addrspace(1) global i8* null, align 8
+// CHECK: @p5 = common local_unnamed_addr addrspace(1) global i8* null, align 8
 generic char *p5;
 
 // Test default initialization of structure.
 
-// CHECK: @S1 = local_unnamed_addr addrspace(1) global %struct.StructTy1 { i8 addrspace(5)* null, i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), i8 addrspace(4)* null, i8 addrspace(1)* null, i8* null }, align 8
+// CHECK: @S1 = weak local_unnamed_addr addrspace(1) global %struct.StructTy1 { i8 addrspace(5)* null, i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), i8 addrspace(4)* null, i8 addrspace(1)* null, i8* null }, align 8
 StructTy1 S1;
 
-// CHECK: @S2 = local_unnamed_addr addrspace(1) global %struct.StructTy2 zeroinitializer, align 8
+// CHECK: @S2 = common local_unnamed_addr addrspace(1) global %struct.StructTy2 zeroinitializer, align 8
 StructTy2 S2;
 
 // Test default initialization of array.
-// CHECK: @A1 = local_unnamed_addr addrspace(1) global [2 x %struct.StructTy1] [%struct.StructTy1 { i8 addrspace(5)* null, i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), i8 addrspace(4)* null, i8 addrspace(1)* null, i8* null }, %struct.StructTy1 { i8 addrspace(5)* null, i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), i8 addrspace(4)* null, i8 addrspace(1)* null, i8* null }], align 8
+// CHECK: @A1 = weak local_unnamed_addr addrspace(1) global [2 x %struct.StructTy1] [%struct.StructTy1 { i8 addrspace(5)* null, i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), i8 addrspace(4)* null, i8 addrspace(1)* null, i8* null }, %struct.StructTy1 { i8 addrspace(5)* null, i8 addrspace(3)* addrspacecast (i8* null to i8 addrspace(3)*), i8 addrspace(4)* null, i8 addrspace(1)* null, i8* null }], align 8
 StructTy1 A1[2];
 
-// CHECK: @A2 = local_unnamed_addr addrspace(1) global [2 x %struct.StructTy2] zeroinitializer, align 8
+// CHECK: @A2 = common local_unnamed_addr addrspace(1) global [2 x %struct.StructTy2] zeroinitializer, align 8
 StructTy2 A2[2];
 
 // Test comparison with 0.
diff --git a/clang/test/Driver/apple-kext-mkernel.c b/clang/test/Driver/apple-kext-mkernel.c
index f056ec898d4dbf..9c60c24e36c81d 100644
--- a/clang/test/Driver/apple-kext-mkernel.c
+++ b/clang/test/Driver/apple-kext-mkernel.c
@@ -4,7 +4,7 @@
 // CHECK-X86: "-disable-red-zone"
 // CHECK-X86: "-fno-builtin"
 // CHECK-X86: "-fno-rtti"
-// CHECK-X86-NOT: "-fcommon"
+// CHECK-X86: "-fno-common"
 
 // RUN: %clang -target x86_64-apple-darwin10 -mkernel -### -fsyntax-only -fbuiltin -fcommon %s 2>&1 | FileCheck --check-prefix=CHECK-X86-2 %s
 
@@ -21,7 +21,7 @@
 // CHECK-ARM-NOT: "-target-feature" "+strict-align"
 // CHECK-ARM: "-fno-builtin"
 // CHECK-ARM: "-fno-rtti"
-// CHECK-ARM-NOT: "-fcommon"
+// CHECK-ARM: "-fno-common"
 
 // RUN: %clang -target x86_64-apple-darwin10 \
 // RUN:   -Werror -fno-builtin -fno-exceptions -fno-common -fno-rtti \
diff --git a/clang/test/Driver/clang_f_opts.c b/clang/test/Driver/clang_f_opts.c
index bda026715c369e..f628f5f40de3ec 100644
--- a/clang/test/Driver/clang_f_opts.c
+++ b/clang/test/Driver/clang_f_opts.c
@@ -12,7 +12,7 @@
 // CHECK-OPTIONS2: -fno-gnu-keywords
 // CHECK-OPTIONS2: -fno-builtin
 // CHECK-OPTIONS2: -fshort-enums
-// CHECK-OPTIONS2-NOT: -fcommon
+// CHECK-OPTIONS2: -fno-common
 // CHECK-OPTIONS2: -fno-show-source-location
 
 // RUN: %clang -### -S -Wwrite-strings %s 2>&1 | FileCheck -check-prefix=WRITE-STRINGS1 %s
diff --git a/clang/test/Driver/fuchsia.c b/clang/test/Driver/fuchsia.c
index 5c1c00061d3af5..185289defccd30 100644
--- a/clang/test/Driver/fuchsia.c
+++ b/clang/test/Driver/fuchsia.c
@@ -22,7 +22,7 @@
 // CHECK-AARCH64: "-fsanitize=shadow-call-stack"
 // CHECK-X86_64: "-fsanitize=safe-stack"
 // CHECK: "-stack-protector" "2"
-// CHECK-NOT: "-fcommon"
+// CHECK: "-fno-common"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "now" "-z" "rodynamic" "-z" "separate-loadable-segments"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
diff --git a/clang/test/Driver/no-common.c b/clang/test/Driver/no-common.c
deleted file mode 100644
index 675de4fee8dc62..00000000000000
--- a/clang/test/Driver/no-common.c
+++ /dev/null
@@ -1,9 +0,0 @@
-// RUN: %clang -target %itanium_abi_triple -### -c %s 2>&1 | \
-// RUN:   FileCheck %s --check-prefix=DEFAULT
-// RUN: %clang -target %itanium_abi_triple -fno-common -### -c %s 2>&1 | \
-// RUN:   FileCheck %s --check-prefix=DEFAULT
-// RUN: %clang -target %itanium_abi_triple -fno-common -fcommon -### -c %s 2>&1 | \
-// RUN:   FileCheck %s --check-prefix=COMMON
-
-// DEFAULT-NOT: "-fcommon"
-// COMMON:      "-fcommon"
diff --git a/clang/test/Driver/xcore-opts.c b/clang/test/Driver/xcore-opts.c
index 8885974ec84aa1..2bf57967092af4 100644
--- a/clang/test/Driver/xcore-opts.c
+++ b/clang/test/Driver/xcore-opts.c
@@ -9,7 +9,7 @@
 // CHECK: "-fno-use-cxa-atexit"
 // CHECK-NOT: "-fcxx-exceptions"
 // CHECK-NOT: "-fexceptions"
-// CHECK-NOT: "-fcommon"
+// CHECK: "-fno-common"
 // CHECK: xcc" "-o"
 // CHECK-NOT: "-fexceptions"
 // CHECK: "-c" "-v" "-g" "-fverbose-asm" "A1Arg" "A2Arg"
@@ -21,7 +21,7 @@
 // CHECK-EXCEP: "-fno-use-cxa-atexit"
 // CHECK-EXCEP: "-fcxx-exceptions"
 // CHECK-EXCEP: "-fexceptions"
-// CHECK-EXCEP-NOT: "-fcommon"
+// CHECK-EXCEP: "-fno-common"
 // CHECK-EXCEP: xcc" "-o"
 // CHECK-EXCEP-NOT: "-fexceptions"
 // CHECK-EXCEP: xcc" "-o"
diff --git a/clang/test/Frontend/ast-codegen.c b/clang/test/Frontend/ast-codegen.c
index b45377850a231a..e1140fdd8b27e4 100644
--- a/clang/test/Frontend/ast-codegen.c
+++ b/clang/test/Frontend/ast-codegen.c
@@ -5,7 +5,7 @@
 // CHECK: module asm "foo"
 __asm__("foo");
 
-// CHECK: @g0 = dso_local global i32 0, align 4
+// CHECK: @g0 = common dso_local global i32 0, align 4
 int g0;
 
 // CHECK: define dso_local i32 @f0()
diff --git a/clang/test/Headers/xmmintrin.c b/clang/test/Headers/xmmintrin.c
index f0f832f81511c3..9b8993e6bb679f 100644
--- a/clang/test/Headers/xmmintrin.c
+++ b/clang/test/Headers/xmmintrin.c
@@ -7,7 +7,7 @@
 // REQUIRES: x86-registered-target
 #include <xmmintrin.h>
 
-// CHECK: @c = global i8 0, align 16
+// CHECK: @c = common global i8 0, align 16
 _MM_ALIGN16 char c;
 
 // Make sure the last step of _mm_cvtps_pi16 converts <4 x i32> to <4 x i16> by
diff --git a/clang/test/PCH/chain-external-defs.c b/clang/test/PCH/chain-external-defs.c
index a58c82c59c83f9..f7c723338996fb 100644
--- a/clang/test/PCH/chain-external-defs.c
+++ b/clang/test/PCH/chain-external-defs.c
@@ -16,11 +16,11 @@
 
 // Z-NOT: @z
 
-// XA: @x = global i32 0
-// XA-NOT: @x = global i32 0
+// XA: @x = common global i32 0
+// XA-NOT: @x = common global i32 0
 
-// YA: @y = global i32 0
-// YA-NOT: @y = global i32 0
+// YA: @y = common global i32 0
+// YA-NOT: @y = common global i32 0
 
 // XB: @x2 = global i32 19
 // XB-NOT: @x2 = global i32 19
@@ -29,17 +29,17 @@ int x2 = 19;
 // YB-NOT: @y2 = global i32 18
 int y2 = 18;
 
-// AA: @incomplete_array = global [1 x i32]
-// AA-NOT: @incomplete_array = global [1 x i32]
-// AB: @incomplete_array2 = global [17 x i32]
-// AB-NOT: @incomplete_array2 = global [17 x i32]
+// AA: @incomplete_array = common global [1 x i32]
+// AA-NOT: @incomplete_array = common global [1 x i32]
+// AB: @incomplete_array2 = common global [17 x i32]
+// AB-NOT: @incomplete_array2 = common global [17 x i32]
 int incomplete_array2[17];
-// AC: @incomplete_array3 = global [1 x i32]
-// AC-NOT: @incomplete_array3 = global [1 x i32]
+// AC: @incomplete_array3 = common global [1 x i32]
+// AC-NOT: @incomplete_array3 = common global [1 x i32]
 int incomplete_array3[];
 
-// S: @s = global %struct.S
-// S-NOT: @s = global %struct.S
+// S: @s = common global %struct.S
+// S-NOT: @s = common global %struct.S
 struct S {
   int x, y;
 };
diff --git a/clang/test/PCH/external-defs.c b/clang/test/PCH/external-defs.c
index e78125d61fdcac..5e906b246bc7c2 100644
--- a/clang/test/PCH/external-defs.c
+++ b/clang/test/PCH/external-defs.c
@@ -3,16 +3,16 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin9 -emit-pch -o %t.pch %S/external-defs.h
 // RUN: %clang_cc1 -triple x86_64-apple-darwin9 -include-pch %t.pch -emit-llvm -o %t %s
 
-// RUN: grep "@x = global i32 0" %t | count 1
+// RUN: grep "@x = common global i32 0" %t | count 1
 // RUN: not grep "@z" %t
 
 // RUN: grep "@x2 = global i32 19" %t | count 1
 int x2 = 19;
 
-// RUN: grep "@incomplete_array = global .*1 x i32" %t | count 1
-// RUN: grep "@incomplete_array2 = global .*17 x i32" %t | count 1
+// RUN: grep "@incomplete_array = common global .*1 x i32" %t | count 1
+// RUN: grep "@incomplete_array2 = common global .*17 x i32" %t | count 1
 int incomplete_array2[17];
-// RUN: grep "@incomplete_array3 = global .*1 x i32" %t | count 1
+// RUN: grep "@incomplete_array3 = common global .*1 x i32" %t | count 1
 int incomplete_array3[];
 
 struct S {
diff --git a/clang/test/PCH/tentative-defs.c b/clang/test/PCH/tentative-defs.c
index f9fee0ca932e70..7163316a93dea1 100644
--- a/clang/test/PCH/tentative-defs.c
+++ b/clang/test/PCH/tentative-defs.c
@@ -1,6 +1,6 @@
 // Test with pch.
-// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -fcommon -emit-pch -o %t.pch %S/tentative-defs.h
-// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -fcommon -include-pch %t.pch -verify -emit-llvm -o %t %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -emit-pch -o %t.pch %S/tentative-defs.h
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 -include-pch %t.pch -verify -emit-llvm -o %t %s
 // REQUIRES: x86-registered-target
 
 // RUN: grep "@variable = common global i32 0" %t | count 1
diff --git a/clang/test/Parser/pragma-visibility2.c b/clang/test/Parser/pragma-visibility2.c
index 272294ca16efae..bcef09ff2b9989 100644
--- a/clang/test/Parser/pragma-visibility2.c
+++ b/clang/test/Parser/pragma-visibility2.c
@@ -6,14 +6,14 @@
 #pragma GCC visibility push(hidden)
 
 int v1;
-// CHECK: @v1 = hidden global i32 0, align 4
+// CHECK: @v1 = common hidden global i32 0, align 4
 
 #pragma GCC visibility pop
 
 int v2;
-// CHECK: @v2 = global i32 0, align 4
+// CHECK: @v2 = common global i32 0, align 4
 
 _Pragma("GCC visibility push(hidden)");
 
 int v3;
-// CHECK: @v3 = hidden global i32 0, align 4
+// CHECK: @v3 = common hidden global i32 0, align 4
diff --git a/compiler-rt/test/asan/TestCases/Linux/odr_c_test.c b/compiler-rt/test/asan/TestCases/Linux/odr_c_test.c
index b9273e49f4c36f..c1423ed30b1b3d 100644
--- a/compiler-rt/test/asan/TestCases/Linux/odr_c_test.c
+++ b/compiler-rt/test/asan/TestCases/Linux/odr_c_test.c
@@ -1,9 +1,9 @@
 // Test that we can properly report an ODR violation
 // between an instrumented global and a non-instrumented global.
 
-// RUN: %clang_asan -fcommon %s -fPIC -shared -o %dynamiclib1  -DFILE1
-// RUN: %clang_asan -fcommon %s -fPIC -shared -o %dynamiclib2  -DFILE2
-// RUN: %clang_asan -fcommon %s -fPIE %ld_flags_rpath_exe1 %ld_flags_rpath_exe2 -o %t
+// RUN: %clang_asan %s -fPIC -shared -o %dynamiclib1  -DFILE1
+// RUN: %clang_asan %s -fPIC -shared -o %dynamiclib2  -DFILE2
+// RUN: %clang_asan %s -fPIE %ld_flags_rpath_exe1 %ld_flags_rpath_exe2 -o %t
 // RUN: not %run %t 2>&1 | FileCheck %s
 //
 // CHECK: The following global variable is not properly aligned.
diff --git a/compiler-rt/test/asan/TestCases/set_shadow_test.c b/compiler-rt/test/asan/TestCases/set_shadow_test.c
index c20e867967ea63..95bbd829ba858e 100644
--- a/compiler-rt/test/asan/TestCases/set_shadow_test.c
+++ b/compiler-rt/test/asan/TestCases/set_shadow_test.c
@@ -21,13 +21,13 @@ void __asan_set_shadow_f3(size_t addr, size_t size);
 void __asan_set_shadow_f5(size_t addr, size_t size);
 void __asan_set_shadow_f8(size_t addr, size_t size);
 
-char* a;
+char a __attribute__((aligned(8)));
 
 void f(long arg) {
   size_t shadow_offset;
   size_t shadow_scale;
   __asan_get_shadow_mapping(&shadow_scale, &shadow_offset);
-  size_t addr = (((size_t)a) >> shadow_scale) + shadow_offset;
+  size_t addr = (((size_t)&a) >> shadow_scale) + shadow_offset;
 
   switch (arg) {
   // X00-NOT: AddressSanitizer
@@ -61,10 +61,9 @@ void f(long arg) {
 int main(int argc, char **argv) {
   assert(argc > 1);
 
-  a = malloc(8);
   long arg = strtol(argv[1], 0, 16);
   f(arg);
-  *a = 1;
+  a = 1;
   printf("PASS\n");
   return 0;
 }