Treat __sync_synchronize and asm("":::"memory") as stronger fences.

test/CodeGen/NaCl/atomics.c

+// Test frontend handling of synchronization builtins which NaCl handles
+// differently.
+// Modified from test/CodeGen/Atomics.c
+// RUN: %clang_cc1 -triple le32-unknown-nacl -emit-llvm %s -o - | FileCheck %s
+
+// CHECK: define void @test_sync_synchronize()
+// CHECK-NEXT: entry:
+void test_sync_synchronize (void)
+{
+  __sync_synchronize ();
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+  // CHECK-NEXT: fence seq_cst
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+
+  // CHECK-NEXT: ret void
+}
+
+// CHECK: define void @test_asm_memory_1()
+// CHECK-NEXT: entry:
+void test_asm_memory_1 (void)
+{
+  asm ("":::"memory");
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+  // CHECK-NEXT: fence seq_cst
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+
+  // CHECK-NEXT: ret void
+}
+
+// CHECK: define void @test_asm_memory_2()
+// CHECK-NEXT: entry:
+void test_asm_memory_2 (void)
+{
+  asm volatile ("":::"memory");
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+  // CHECK-NEXT: fence seq_cst
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+
+  // CHECK-NEXT: ret void
+}
+
+// CHECK: define void @test_asm_memory_3()
+// CHECK-NEXT: entry:
+void test_asm_memory_3 (void)
+{
+  __asm__ ("":::"memory");
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+  // CHECK-NEXT: fence seq_cst
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+
+  // CHECK-NEXT: ret void
+}
+
+// CHECK: define void @test_asm_memory_4()
+// CHECK-NEXT: entry:
+void test_asm_memory_4 (void)
+{
+  __asm__ __volatile__ ("":::"memory");
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+  // CHECK-NEXT: fence seq_cst
+  // CHECK-NEXT: call void asm sideeffect "", "~{memory}"()
+
+  // CHECK-NEXT: ret void
+}