Remove unused ShouldFoldAtomicFences flag.

I think it's almost impossible to fold atomic fences profitably under
LLVM/C++11 semantics. As a result, this is now unused and just
cluttering up the target interface.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179940 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetLowering.h

@@ -810,13 +810,6 @@ public:
     return PrefLoopAlignment;
   }
 
-  /// getShouldFoldAtomicFences - return whether the combiner should fold
-  /// fence MEMBARRIER instructions into the atomic intrinsic instructions.
-  ///
-  bool getShouldFoldAtomicFences() const {
-    return ShouldFoldAtomicFences;
-  }
-
   /// getInsertFencesFor - return whether the DAG builder should automatically
   /// insert fences and reduce ordering for atomics.
   ///
@@ -1101,12 +1094,6 @@ protected:
     MinStackArgumentAlignment = Align;
   }
 
-  /// setShouldFoldAtomicFences - Set if the target's implementation of the
-  /// atomic operation intrinsics includes locking. Default is false.
-  void setShouldFoldAtomicFences(bool fold) {
-    ShouldFoldAtomicFences = fold;
-  }
-
   /// setInsertFencesForAtomic - Set if the DAG builder should
   /// automatically insert fences and reduce the order of atomic memory
   /// operations to Monotonic.
@@ -1364,11 +1351,6 @@ private:
   ///
   unsigned PrefLoopAlignment;
 
-  /// ShouldFoldAtomicFences - Whether fencing MEMBARRIER instructions should
-  /// be folded into the enclosed atomic intrinsic instruction by the
-  /// combiner.
-  bool ShouldFoldAtomicFences;
-
   /// InsertFencesForAtomic - Whether the DAG builder should automatically
   /// insert fences and reduce ordering for atomics.  (This will be set for
   /// for most architectures with weak memory ordering.)

lib/CodeGen/TargetLoweringBase.cpp

@@ -647,7 +647,6 @@ TargetLoweringBase::TargetLoweringBase(const TargetMachine &tm,
   PrefFunctionAlignment = 0;
   PrefLoopAlignment = 0;
   MinStackArgumentAlignment = 1;
-  ShouldFoldAtomicFences = false;
   InsertFencesForAtomic = false;
   SupportJumpTables = true;
   MinimumJumpTableEntries = 4;

lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -59,10 +59,6 @@ AArch64TargetLowering::AArch64TargetLowering(AArch64TargetMachine &TM)
 
   computeRegisterProperties();
 
-  // We have particularly efficient implementations of atomic fences if they can
-  // be combined with nearby atomic loads and stores.
-  setShouldFoldAtomicFences(true);
-
   // We combine OR nodes for bitfield and NEON BSL operations.
   setTargetDAGCombine(ISD::OR);
 

lib/Target/ARM/ARMISelLowering.cpp

@@ -763,8 +763,6 @@ ARMTargetLowering::ARMTargetLowering(TargetMachine &TM)
     // Unordered/Monotonic case.
     setOperationAction(ISD::ATOMIC_LOAD, MVT::i32, Custom);
     setOperationAction(ISD::ATOMIC_STORE, MVT::i32, Custom);
-    // Since the libcalls include locking, fold in the fences
-    setShouldFoldAtomicFences(true);
   }
 
   setOperationAction(ISD::PREFETCH,         MVT::Other, Custom);

lib/Target/X86/X86ISelLowering.cpp

@@ -528,13 +528,6 @@ void X86TargetLowering::resetOperationActions() {
 
   setOperationAction(ISD::ATOMIC_FENCE  , MVT::Other, Custom);
 
-  // On X86 and X86-64, atomic operations are lowered to locked instructions.
-  // Locked instructions, in turn, have implicit fence semantics (all memory
-  // operations are flushed before issuing the locked instruction, and they
-  // are not buffered), so we can fold away the common pattern of
-  // fence-atomic-fence.
-  setShouldFoldAtomicFences(true);
-
   // Expand certain atomics
   for (unsigned i = 0; i != array_lengthof(IntVTs); ++i) {
     MVT VT = IntVTs[i];