1 //===-- AtomicExpandUtils.h - Utilities for expanding atomic instructions -===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "llvm/ADT/STLExtras.h" 11 #include "llvm/IR/IRBuilder.h" 12 13 namespace llvm { 14 class Value; 15 class AtomicRMWInst; 16 17 18 /// Parameters (see the expansion example below): 19 /// (the builder, %addr, %loaded, %new_val, ordering, 20 /// /* OUT */ %success, /* OUT */ %new_loaded) 21 typedef function_ref<void(IRBuilder<> &, Value *, Value *, Value *, 22 AtomicOrdering, Value *&, Value *&)> CreateCmpXchgInstFun; 23 24 /// \brief Expand an atomic RMW instruction into a loop utilizing 25 /// cmpxchg. You'll want to make sure your target machine likes cmpxchg 26 /// instructions in the first place and that there isn't another, better, 27 /// transformation available (for example AArch32/AArch64 have linked loads). 28 /// 29 /// This is useful in passes which can't rewrite the more exotic RMW 30 /// instructions directly into a platform specific intrinsics (because, say, 31 /// those intrinsics don't exist). If such a pass is able to expand cmpxchg 32 /// instructions directly however, then, with this function, it could avoid two 33 /// extra module passes (avoiding passes by `-atomic-expand` and itself). A 34 /// specific example would be PNaCl's `RewriteAtomics` pass. 35 /// 36 /// Given: atomicrmw some_op iN* %addr, iN %incr ordering 37 /// 38 /// The standard expansion we produce is: 39 /// [...] 40 /// %init_loaded = load atomic iN* %addr 41 /// br label %loop 42 /// loop: 43 /// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ] 44 /// %new = some_op iN %loaded, %incr 45 /// ; This is what -atomic-expand will produce using this function on i686 targets: 46 /// %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val 47 /// %new_loaded = extractvalue { iN, i1 } %pair, 0 48 /// %success = extractvalue { iN, i1 } %pair, 1 49 /// ; End callback produced IR 50 /// br i1 %success, label %atomicrmw.end, label %loop 51 /// atomicrmw.end: 52 /// [...] 53 /// 54 /// Returns true if the containing function was modified. 55 bool 56 expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun Factory); 57 } 58