Import prebuilt clang toolchain for linux.
diff --git a/linux-x64/clang/include/llvm/CodeGen/AtomicExpandUtils.h b/linux-x64/clang/include/llvm/CodeGen/AtomicExpandUtils.h
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+++ b/linux-x64/clang/include/llvm/CodeGen/AtomicExpandUtils.h
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+//===- AtomicExpandUtils.h - Utilities for expanding atomic instructions --===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_ATOMICEXPANDUTILS_H
+#define LLVM_CODEGEN_ATOMICEXPANDUTILS_H
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/Support/AtomicOrdering.h"
+
+namespace llvm {
+
+class AtomicRMWInst;
+class Value;
+
+/// Parameters (see the expansion example below):
+/// (the builder, %addr, %loaded, %new_val, ordering,
+/// /* OUT */ %success, /* OUT */ %new_loaded)
+using CreateCmpXchgInstFun =
+ function_ref<void(IRBuilder<> &, Value *, Value *, Value *, AtomicOrdering,
+ Value *&, Value *&)>;
+
+/// \brief Expand an atomic RMW instruction into a loop utilizing
+/// cmpxchg. You'll want to make sure your target machine likes cmpxchg
+/// instructions in the first place and that there isn't another, better,
+/// transformation available (for example AArch32/AArch64 have linked loads).
+///
+/// This is useful in passes which can't rewrite the more exotic RMW
+/// instructions directly into a platform specific intrinsics (because, say,
+/// those intrinsics don't exist). If such a pass is able to expand cmpxchg
+/// instructions directly however, then, with this function, it could avoid two
+/// extra module passes (avoiding passes by `-atomic-expand` and itself). A
+/// specific example would be PNaCl's `RewriteAtomics` pass.
+///
+/// Given: atomicrmw some_op iN* %addr, iN %incr ordering
+///
+/// The standard expansion we produce is:
+/// [...]
+/// %init_loaded = load atomic iN* %addr
+/// br label %loop
+/// loop:
+/// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ]
+/// %new = some_op iN %loaded, %incr
+/// ; This is what -atomic-expand will produce using this function on i686
+/// targets:
+/// %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val
+/// %new_loaded = extractvalue { iN, i1 } %pair, 0
+/// %success = extractvalue { iN, i1 } %pair, 1
+/// ; End callback produced IR
+/// br i1 %success, label %atomicrmw.end, label %loop
+/// atomicrmw.end:
+/// [...]
+///
+/// Returns true if the containing function was modified.
+bool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun Factory);
+
+} // end namespace llvm
+
+#endif // LLVM_CODEGEN_ATOMICEXPANDUTILS_H