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 #ifndef LLVM_CODEGEN_ATOMICEXPANDUTILS_H 11 #define LLVM_CODEGEN_ATOMICEXPANDUTILS_H 12 13 #include "llvm/ADT/STLExtras.h" 14 #include "llvm/IR/IRBuilder.h" 15 #include "llvm/Support/AtomicOrdering.h" 16 17 namespace llvm { 18 19 class AtomicRMWInst; 20 class Value; 21 22 /// Parameters (see the expansion example below): 23 /// (the builder, %addr, %loaded, %new_val, ordering, 24 /// /* OUT */ %success, /* OUT */ %new_loaded) 25 using CreateCmpXchgInstFun = 26 function_ref<void(IRBuilder<> &, Value *, Value *, Value *, AtomicOrdering, 27 Value *&, Value *&)>; 28 29 /// \brief Expand an atomic RMW instruction into a loop utilizing 30 /// cmpxchg. You'll want to make sure your target machine likes cmpxchg 31 /// instructions in the first place and that there isn't another, better, 32 /// transformation available (for example AArch32/AArch64 have linked loads). 33 /// 34 /// This is useful in passes which can't rewrite the more exotic RMW 35 /// instructions directly into a platform specific intrinsics (because, say, 36 /// those intrinsics don't exist). If such a pass is able to expand cmpxchg 37 /// instructions directly however, then, with this function, it could avoid two 38 /// extra module passes (avoiding passes by `-atomic-expand` and itself). A 39 /// specific example would be PNaCl's `RewriteAtomics` pass. 40 /// 41 /// Given: atomicrmw some_op iN* %addr, iN %incr ordering 42 /// 43 /// The standard expansion we produce is: 44 /// [...] 45 /// %init_loaded = load atomic iN* %addr 46 /// br label %loop 47 /// loop: 48 /// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ] 49 /// %new = some_op iN %loaded, %incr 50 /// ; This is what -atomic-expand will produce using this function on i686 51 /// targets: 52 /// %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val 53 /// %new_loaded = extractvalue { iN, i1 } %pair, 0 54 /// %success = extractvalue { iN, i1 } %pair, 1 55 /// ; End callback produced IR 56 /// br i1 %success, label %atomicrmw.end, label %loop 57 /// atomicrmw.end: 58 /// [...] 59 /// 60 /// Returns true if the containing function was modified. 61 bool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun Factory); 62 63 } // end namespace llvm 64 65 #endif // LLVM_CODEGEN_ATOMICEXPANDUTILS_H 66
