r181728 - Use atomic instructions on ARM linux.

[Rafael Espindola]

Author: rafael
Date: Mon May 13 15:09:47 2013
New Revision: 181728

URL: http://llvm.org/viewvc/llvm-project?rev=181728&view=rev
Log:
Use atomic instructions on ARM linux.

This is safe given how the pre-v6 atomic ops funcions in libgcc are
implemented.

This fixes pr15429.

Added:
    cfe/trunk/test/CodeGen/linux-arm-atomic.c
Modified:
    cfe/trunk/lib/Basic/Targets.cpp

Modified: cfe/trunk/lib/Basic/Targets.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Basic/Targets.cpp?rev=181728&r1=181727&r2=181728&view=diff
==============================================================================
--- cfe/trunk/lib/Basic/Targets.cpp (original)
+++ cfe/trunk/lib/Basic/Targets.cpp Mon May 13 15:09:47 2013
@@ -3527,6 +3527,20 @@ class ARMTargetInfo : public TargetInfo
 
   static const Builtin::Info BuiltinInfo[];
 
+  static bool shouldUseInlineAtomic(const llvm::Triple &T) {
+    // On linux, binaries targeting old cpus call functions in libgcc to
+    // perform atomic operations. The implementation in libgcc then calls into
+    // the kernel which on armv6 and newer uses ldrex and strex. The net result
+    // is that if we assume the kernel is at least as recent as the hardware,
+    // it is safe to use atomic instructions on armv6 and newer.
+    if (T.getOS() != llvm::Triple::Linux)
+     return false;
+    StringRef ArchName = T.getArchName();
+    if (ArchName.startswith("armv6") || ArchName.startswith("armv7"))
+      return true;
+    return false;
+  }
+
 public:
   ARMTargetInfo(const std::string &TripleStr)
     : TargetInfo(TripleStr), ABI("aapcs-linux"), CPU("arm1136j-s"), IsAAPCS(true)
@@ -3559,8 +3573,9 @@ public:
     TheCXXABI.set(TargetCXXABI::GenericARM);
 
     // ARM has atomics up to 8 bytes
-    // FIXME: Set MaxAtomicInlineWidth if we have the feature v6e
     MaxAtomicPromoteWidth = 64;
+    if (shouldUseInlineAtomic(getTriple()))
+      MaxAtomicInlineWidth = 64;
 
     // Do force alignment of members that follow zero length bitfields.  If
     // the alignment of the zero-length bitfield is greater than the member 

Added: cfe/trunk/test/CodeGen/linux-arm-atomic.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/linux-arm-atomic.c?rev=181728&view=auto
==============================================================================
--- cfe/trunk/test/CodeGen/linux-arm-atomic.c (added)
+++ cfe/trunk/test/CodeGen/linux-arm-atomic.c Mon May 13 15:09:47 2013
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=armv7-unknown-linux | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=armv6-unknown-linux | FileCheck %s
+
+typedef int _Atomic_word;
+_Atomic_word exchange_and_add(volatile _Atomic_word *__mem, int __val) {
+  return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL);
+}
+
+// CHECK: define {{.*}} @exchange_and_add
+// CHECK: atomicrmw {{.*}} add