Index: cfe/trunk/lib/Basic/Targets/X86.h
===================================================================
--- cfe/trunk/lib/Basic/Targets/X86.h
+++ cfe/trunk/lib/Basic/Targets/X86.h
@@ -100,6 +100,7 @@
   bool HasRetpoline = false;
   bool HasRetpolineExternalThunk = false;
 
+protected:
   /// \brief Enumeration of all of the X86 CPUs supported by Clang.
   ///
   /// Each enumeration represents a particular CPU supported by Clang. These
@@ -325,9 +326,11 @@
          (1 << TargetInfo::LongDouble));
 
     // x86-32 has atomics up to 8 bytes
-    // FIXME: Check that we actually have cmpxchg8b before setting
-    // MaxAtomicInlineWidth. (cmpxchg8b is an i586 instruction.)
-    MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
+    CPUKind Kind = getCPUKind(Opts.CPU);
+    if (Kind >= CK_i586 || Kind == CK_Generic)
+      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
+    else if (Kind >= CK_i486)
+      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 32;
   }
 
   BuiltinVaListKind getBuiltinVaListKind() const override {
Index: cfe/trunk/test/CodeGenCXX/atomic-inline.cpp
===================================================================
--- cfe/trunk/test/CodeGenCXX/atomic-inline.cpp
+++ cfe/trunk/test/CodeGenCXX/atomic-inline.cpp
@@ -1,6 +1,52 @@
 // RUN: %clang_cc1 %s -std=c++11 -emit-llvm -o - -triple=x86_64-linux-gnu | FileCheck %s
 // RUN: %clang_cc1 %s -std=c++11 -emit-llvm -o - -triple=x86_64-linux-gnu -target-cpu core2 | FileCheck %s --check-prefix=CORE2
-// Check the atomic code generation for cpu targets w/wo cx16 support.
+// RUN: %clang_cc1 %s -std=c++11 -emit-llvm -o - -triple=i386-linux-gnu -target-cpu i386 | FileCheck %s --check-prefix=I386
+// RUN: %clang_cc1 %s -std=c++11 -emit-llvm -o - -triple=i386-linux-gnu -target-cpu i486 | FileCheck %s --check-prefix=I486
+// Check the atomic code generation for cpu targets w/wo cx, cx8 and cx16 support.
+
+struct alignas(4) AM4 {
+  short f1, f2;
+};
+AM4 m4;
+AM4 load4() {
+  AM4 am;
+  // CHECK-LABEL: @_Z5load4v
+  // CHECK: load atomic i32, {{.*}} monotonic
+  // CORE2-LABEL: @_Z5load4v
+  // CORE2: load atomic i32, {{.*}} monotonic
+  // I386-LABEL: @_Z5load4v
+  // I386: call i32 @__atomic_load_4
+  // I486-LABEL: @_Z5load4v
+  // I486: load atomic i32, {{.*}} monotonic
+  __atomic_load(&m4, &am, 0);
+  return am;
+}
+
+AM4 s4;
+void store4() {
+  // CHECK-LABEL: @_Z6store4v
+  // CHECK: store atomic i32 {{.*}} monotonic
+  // CORE2-LABEL: @_Z6store4v
+  // CORE2: store atomic i32 {{.*}} monotonic
+  // I386-LABEL: @_Z6store4v
+  // I386: call void @__atomic_store_4
+  // I486-LABEL: @_Z6store4v
+  // I486: store atomic i32 {{.*}} monotonic
+  __atomic_store(&m4, &s4, 0);
+}
+
+bool cmpxchg4() {
+  AM4 am;
+  // CHECK-LABEL: @_Z8cmpxchg4v
+  // CHECK: cmpxchg i32* {{.*}} monotonic
+  // CORE2-LABEL: @_Z8cmpxchg4v
+  // CORE2: cmpxchg i32* {{.*}} monotonic
+  // I386-LABEL: @_Z8cmpxchg4v
+  // I386: call zeroext i1 @__atomic_compare_exchange_4
+  // I486-LABEL: @_Z8cmpxchg4v
+  // I486: cmpxchg i32* {{.*}} monotonic
+  return __atomic_compare_exchange(&m4, &s4, &am, 0, 0, 0);
+}
 
 struct alignas(8) AM8 {
   int f1, f2;
@@ -12,6 +58,10 @@
   // CHECK: load atomic i64, {{.*}} monotonic
   // CORE2-LABEL: @_Z5load8v
   // CORE2: load atomic i64, {{.*}} monotonic
+  // I386-LABEL: @_Z5load8v
+  // I386: call i64 @__atomic_load_8
+  // I486-LABEL: @_Z5load8v
+  // I486: call i64 @__atomic_load_8
   __atomic_load(&m8, &am, 0);
   return am;
 }
@@ -22,6 +72,10 @@
   // CHECK: store atomic i64 {{.*}} monotonic
   // CORE2-LABEL: @_Z6store8v
   // CORE2: store atomic i64 {{.*}} monotonic
+  // I386-LABEL: @_Z6store8v
+  // I386: call void @__atomic_store_8
+  // I486-LABEL: @_Z6store8v
+  // I486: call void @__atomic_store_8
   __atomic_store(&m8, &s8, 0);
 }
 
@@ -31,6 +85,10 @@
   // CHECK: cmpxchg i64* {{.*}} monotonic
   // CORE2-LABEL: @_Z8cmpxchg8v
   // CORE2: cmpxchg i64* {{.*}} monotonic
+  // I386-LABEL: @_Z8cmpxchg8v
+  // I386: call zeroext i1 @__atomic_compare_exchange_8
+  // I486-LABEL: @_Z8cmpxchg8v
+  // I486: call zeroext i1 @__atomic_compare_exchange_8
   return __atomic_compare_exchange(&m8, &s8, &am, 0, 0, 0);
 }
 
@@ -66,4 +124,3 @@
   // CORE2: cmpxchg i128* {{.*}} monotonic
   return __atomic_compare_exchange(&m16, &s16, &am, 0, 0, 0);
 }
-