//===-- 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. // //===----------------------------------------------------------------------===// #include "llvm/ADT/STLExtras.h" #include "llvm/IR/IRBuilder.h" namespace llvm { class Value; class AtomicRMWInst; /// Parameters (see the expansion example below): /// (the builder, %addr, %loaded, %new_val, ordering, /// /* OUT */ %success, /* OUT */ %new_loaded) typedef function_ref<void(IRBuilder<> &, Value *, Value *, Value *, AtomicOrdering, Value *&, Value *&)> CreateCmpXchgInstFun; /// \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); }