Index: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6543,6 +6543,10 @@
     "asm constraint has an unexpected number of alternatives: %0 vs %1">;
   def err_asm_incomplete_type : Error<"asm operand has incomplete type %0">;
   def err_asm_unknown_register_name : Error<"unknown register name '%0' in asm">;
+  def err_asm_invalid_global_var_reg : Error<"register '%0' unsuitable for "
+    "global register variables on this target">;
+  def err_asm_register_size_mismatch : Error<"size of register '%0' does not "
+    "match variable size">;
   def err_asm_bad_register_type : Error<"bad type for named register variable">;
   def err_asm_invalid_input_size : Error<
     "invalid input size for constraint '%0'">;
Index: cfe/trunk/include/clang/Basic/TargetInfo.h
===================================================================
--- cfe/trunk/include/clang/Basic/TargetInfo.h
+++ cfe/trunk/include/clang/Basic/TargetInfo.h
@@ -644,6 +644,19 @@
     }
   };
 
+  /// \brief Validate register name used for global register variables.
+  ///
+  /// This function returns true if the register passed in RegName can be used
+  /// for global register variables on this target. In addition, it returns
+  /// true in HasSizeMismatch if the size of the register doesn't match the
+  /// variable size passed in RegSize.
+  virtual bool validateGlobalRegisterVariable(StringRef RegName,
+                                              unsigned RegSize,
+                                              bool &HasSizeMismatch) const {
+    HasSizeMismatch = false;
+    return true;
+  }
+
   // validateOutputConstraint, validateInputConstraint - Checks that
   // a constraint is valid and provides information about it.
   // FIXME: These should return a real error instead of just true/false.
Index: cfe/trunk/lib/Basic/Targets.cpp
===================================================================
--- cfe/trunk/lib/Basic/Targets.cpp
+++ cfe/trunk/lib/Basic/Targets.cpp
@@ -2358,6 +2358,20 @@
   bool validateAsmConstraint(const char *&Name,
                              TargetInfo::ConstraintInfo &info) const override;
 
+  bool validateGlobalRegisterVariable(StringRef RegName,
+                                      unsigned RegSize,
+                                      bool &HasSizeMismatch) const override {
+    // esp and ebp are the only 32-bit registers the x86 backend can currently
+    // handle.
+    if (RegName.equals("esp") || RegName.equals("ebp")) {
+      // Check that the register size is 32-bit.
+      HasSizeMismatch = RegSize != 32;
+      return true;
+    }
+
+    return false;
+  }
+
   bool validateOutputSize(StringRef Constraint, unsigned Size) const override;
 
   bool validateInputSize(StringRef Constraint, unsigned Size) const override;
@@ -3974,6 +3988,22 @@
 
   // for x32 we need it here explicitly
   bool hasInt128Type() const override { return true; }
+
+  bool validateGlobalRegisterVariable(StringRef RegName,
+                                      unsigned RegSize,
+                                      bool &HasSizeMismatch) const override {
+    // rsp and rbp are the only 64-bit registers the x86 backend can currently
+    // handle.
+    if (RegName.equals("rsp") || RegName.equals("rbp")) {
+      // Check that the register size is 64-bit.
+      HasSizeMismatch = RegSize != 64;
+      return true;
+    }
+
+    // Check if the register is a 32-bit register the backend can handle.
+    return X86TargetInfo::validateGlobalRegisterVariable(RegName, RegSize,
+                                                         HasSizeMismatch);
+  }
 };
 
 // x86-64 Windows target
Index: cfe/trunk/lib/Sema/SemaDecl.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp
+++ cfe/trunk/lib/Sema/SemaDecl.cpp
@@ -6079,9 +6079,20 @@
       }
     } else if (SC == SC_Register) {
       // Global Named register
-      if (!Context.getTargetInfo().isValidGCCRegisterName(Label) &&
-          DeclAttrsMatchCUDAMode(getLangOpts(), NewVD))
-        Diag(E->getExprLoc(), diag::err_asm_unknown_register_name) << Label;
+      if (DeclAttrsMatchCUDAMode(getLangOpts(), NewVD)) {
+        const auto &TI = Context.getTargetInfo();
+        bool HasSizeMismatch;
+
+        if (!TI.isValidGCCRegisterName(Label))
+          Diag(E->getExprLoc(), diag::err_asm_unknown_register_name) << Label;
+        else if (!TI.validateGlobalRegisterVariable(Label,
+                                                    Context.getTypeSize(R),
+                                                    HasSizeMismatch))
+          Diag(E->getExprLoc(), diag::err_asm_invalid_global_var_reg) << Label;
+        else if (HasSizeMismatch)
+          Diag(E->getExprLoc(), diag::err_asm_register_size_mismatch) << Label;
+      }
+
       if (!R->isIntegralType(Context) && !R->isPointerType()) {
         Diag(D.getLocStart(), diag::err_asm_bad_register_type);
         NewVD->setInvalidDecl(true);
Index: cfe/trunk/test/CodeGen/named_reg_global.c
===================================================================
--- cfe/trunk/test/CodeGen/named_reg_global.c
+++ cfe/trunk/test/CodeGen/named_reg_global.c
@@ -1,16 +1,26 @@
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
-// RUN: %clang_cc1 -triple arm64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
-// RUN: %clang_cc1 -triple armv7-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-X86-64
+// RUN: %clang_cc1 -triple arm64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-ARM
+// RUN: %clang_cc1 -triple armv7-linux-gnu -S -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-ARM
 
 // CHECK-NOT: @sp = common global
+
+#if defined(__x86_64__)
+register unsigned long current_stack_pointer asm("rsp");
+#else
 register unsigned long current_stack_pointer asm("sp");
+#endif
+
 struct p4_Thread {
   struct {
     int len;
   } word;
 };
 // Testing pointer types as well
+#if defined(__x86_64__)
+register struct p4_Thread *p4TH asm("rsp");
+#else
 register struct p4_Thread *p4TH asm("sp");
+#endif
 
 // CHECK: define{{.*}} i[[bits:[0-9]+]] @get_stack_pointer_addr()
 // CHECK: [[ret:%[0-9]+]] = call i[[bits]] @llvm.read_register.i[[bits]](metadata !0)
@@ -43,5 +53,7 @@
 // CHECK: %[[regw:[0-9]+]] = ptrtoint %struct.p4_Thread* %{{.*}} to i[[bits]]
 // CHECK: call void @llvm.write_register.i[[bits]](metadata !0, i[[bits]] %[[regw]])
 
-// CHECK: !llvm.named.register.sp = !{!0}
-// CHECK: !0 = !{!"sp"}
+// CHECK-X86-64: !llvm.named.register.rsp = !{!0}
+// CHECK-X86-64: !0 = !{!"rsp"}
+// CHECK-ARM: !llvm.named.register.sp = !{!0}
+// CHECK-ARM: !0 = !{!"sp"}
Index: cfe/trunk/test/OpenMP/atomic_capture_codegen.cpp
===================================================================
--- cfe/trunk/test/OpenMP/atomic_capture_codegen.cpp
+++ cfe/trunk/test/OpenMP/atomic_capture_codegen.cpp
@@ -72,7 +72,10 @@
 typedef float float2 __attribute__((ext_vector_type(2)));
 float2 float2x;
 
-register int rix __asm__("0");
+// Register "0" is currently an invalid register for global register variables.
+// Use "esp" instead of "0".
+// register int rix __asm__("0");
+register int rix __asm__("esp");
 
 int main() {
 // CHECK: [[PREV:%.+]] = atomicrmw add i8* @{{.+}}, i8 1 monotonic
Index: cfe/trunk/test/OpenMP/atomic_read_codegen.c
===================================================================
--- cfe/trunk/test/OpenMP/atomic_read_codegen.c
+++ cfe/trunk/test/OpenMP/atomic_read_codegen.c
@@ -72,7 +72,10 @@
 typedef float float2 __attribute__((ext_vector_type(2)));
 float2 float2x;
 
-register int rix __asm__("0");
+// Register "0" is currently an invalid register for global register variables.
+// Use "esp" instead of "0".
+// register int rix __asm__("0");
+register int rix __asm__("esp");
 
 int main() {
 // CHECK: load atomic i8, i8*
Index: cfe/trunk/test/OpenMP/atomic_update_codegen.cpp
===================================================================
--- cfe/trunk/test/OpenMP/atomic_update_codegen.cpp
+++ cfe/trunk/test/OpenMP/atomic_update_codegen.cpp
@@ -72,7 +72,10 @@
 typedef float float2 __attribute__((ext_vector_type(2)));
 float2 float2x;
 
-register int rix __asm__("0");
+// Register "0" is currently an invalid register for global register variables.
+// Use "esp" instead of "0".
+// register int rix __asm__("0");
+register int rix __asm__("esp");
 
 int main() {
 // CHECK-NOT: atomicrmw
Index: cfe/trunk/test/OpenMP/atomic_write_codegen.c
===================================================================
--- cfe/trunk/test/OpenMP/atomic_write_codegen.c
+++ cfe/trunk/test/OpenMP/atomic_write_codegen.c
@@ -72,7 +72,10 @@
 typedef float float2 __attribute__((ext_vector_type(2)));
 float2 float2x;
 
-register int rix __asm__("0");
+// Register "0" is currently an invalid register for global register variables.
+// Use "esp" instead of "0".
+// register int rix __asm__("0");
+register int rix __asm__("esp");
 
 int main() {
 // CHECK: load i8, i8*
Index: cfe/trunk/test/OpenMP/for_loop_messages.cpp
===================================================================
--- cfe/trunk/test/OpenMP/for_loop_messages.cpp
+++ cfe/trunk/test/OpenMP/for_loop_messages.cpp
@@ -13,7 +13,9 @@
 #pragma omp threadprivate(sii)
 static int globalii;
 
-register int reg0 __asm__("0");
+// Currently, we cannot use "0" for global register variables.
+// register int reg0 __asm__("0");
+int reg0;
 
 int test_iteration_spaces() {
   const int N = 100;
Index: cfe/trunk/test/OpenMP/threadprivate_messages.cpp
===================================================================
--- cfe/trunk/test/OpenMP/threadprivate_messages.cpp
+++ cfe/trunk/test/OpenMP/threadprivate_messages.cpp
@@ -96,7 +96,10 @@
 static __thread int t; // expected-note {{'t' defined here}}
 #pragma omp threadprivate (t) // expected-error {{variable 't' cannot be threadprivate because it is thread-local}}
 
-register int reg0 __asm__("0"); // expected-note {{'reg0' defined here}}
+// Register "0" is currently an invalid register for global register variables.
+// Use "esp" instead of "0".
+// register int reg0 __asm__("0");
+register int reg0 __asm__("esp"); // expected-note {{'reg0' defined here}}
 #pragma omp threadprivate (reg0) // expected-error {{variable 'reg0' cannot be threadprivate because it is a global named register variable}}
 
 int o; // expected-note {{candidate found by name lookup is 'o'}}
Index: cfe/trunk/test/Sema/asm.c
===================================================================
--- cfe/trunk/test/Sema/asm.c
+++ cfe/trunk/test/Sema/asm.c
@@ -1,7 +1,6 @@
 // RUN: %clang_cc1 %s -Wno-private-extern -triple i386-pc-linux-gnu -verify -fsyntax-only
 
 
-
 void f() {
   int i;
 
@@ -154,10 +153,13 @@
 // PR19837
 struct foo {
   int a;
-  char b;
 };
-register struct foo bar asm("sp"); // expected-error {{bad type for named register variable}}
-register float baz asm("sp"); // expected-error {{bad type for named register variable}}
+register struct foo bar asm("esp"); // expected-error {{bad type for named register variable}}
+register float baz asm("esp"); // expected-error {{bad type for named register variable}}
+
+register int r0 asm ("edi"); // expected-error {{register 'edi' unsuitable for global register variables on this target}}
+register long long r1 asm ("esp"); // expected-error {{size of register 'esp' does not match variable size}}
+register int r2 asm ("esp");
 
 double f_output_constraint(void) {
   double result;
@@ -212,7 +214,7 @@
   unsigned int field3 : 3;
 } test16_foo;
 typedef __attribute__((vector_size(16))) int test16_bar;
-register int test16_baz asm("rbx");
+register int test16_baz asm("esp");
 
 void test16()
 {
Index: cfe/trunk/test/SemaCUDA/asm-constraints-mixed.cu
===================================================================
--- cfe/trunk/test/SemaCUDA/asm-constraints-mixed.cu
+++ cfe/trunk/test/SemaCUDA/asm-constraints-mixed.cu
@@ -5,14 +5,14 @@
 
 __attribute__((device)) register long global_dev_reg asm("r0");
 __attribute__((device)) register long
-    global_dev_hreg asm("rax"); // device-side error
+    global_dev_hreg asm("rsp"); // device-side error
 
-register long global_host_reg asm("rax");
+register long global_host_reg asm("rsp");
 register long global_host_dreg asm("r0"); // host-side error
 
 __attribute__((device)) void df() {
   register long local_dev_reg asm("r0");
-  register long local_host_reg asm("rax"); // device-side error
+  register long local_host_reg asm("rsp"); // device-side error
   short h;
   // asm with PTX constraints. Some of them are PTX-specific.
   __asm__("dont care" : "=h"(h) : "f"(0.0), "d"(0.0), "h"(0), "r"(0), "l"(0));
@@ -20,7 +20,7 @@
 
 void hf() {
   register long local_dev_reg asm("r0"); // host-side error
-  register long local_host_reg asm("rax");
+  register long local_host_reg asm("rsp");
   int a;
   // Asm with x86 constraints and registers that are not supported by PTX.
   __asm__("dont care" : "=a"(a) : "a"(0), "b"(0), "c"(0) : "flags");
@@ -30,8 +30,8 @@
 // We should only see errors relevant to current compilation mode.
 #if defined(__CUDA_ARCH__)
 // Device-side compilation:
-// expected-error@8 {{unknown register name 'rax' in asm}}
-// expected-error@15 {{unknown register name 'rax' in asm}}
+// expected-error@8 {{unknown register name 'rsp' in asm}}
+// expected-error@15 {{unknown register name 'rsp' in asm}}
 #else
 // Host-side compilation:
 // expected-error@11 {{unknown register name 'r0' in asm}}