AtomicExpandUtils.h revision 321369
1321369Sdim//===- AtomicExpandUtils.h - Utilities for expanding atomic instructions --===// 2292915Sdim// 3292915Sdim// The LLVM Compiler Infrastructure 4292915Sdim// 5292915Sdim// This file is distributed under the University of Illinois Open Source 6292915Sdim// License. See LICENSE.TXT for details. 7292915Sdim// 8292915Sdim//===----------------------------------------------------------------------===// 9292915Sdim 10321369Sdim#ifndef LLVM_CODEGEN_ATOMICEXPANDUTILS_H 11321369Sdim#define LLVM_CODEGEN_ATOMICEXPANDUTILS_H 12321369Sdim 13292915Sdim#include "llvm/ADT/STLExtras.h" 14292915Sdim#include "llvm/IR/IRBuilder.h" 15321369Sdim#include "llvm/Support/AtomicOrdering.h" 16292915Sdim 17292915Sdimnamespace llvm { 18321369Sdim 19321369Sdimclass AtomicRMWInst; 20292915Sdimclass Value; 21292915Sdim 22292915Sdim/// Parameters (see the expansion example below): 23292915Sdim/// (the builder, %addr, %loaded, %new_val, ordering, 24292915Sdim/// /* OUT */ %success, /* OUT */ %new_loaded) 25321369Sdimusing CreateCmpXchgInstFun = 26321369Sdim function_ref<void(IRBuilder<> &, Value *, Value *, Value *, AtomicOrdering, 27321369Sdim Value *&, Value *&)>; 28292915Sdim 29292915Sdim/// \brief Expand an atomic RMW instruction into a loop utilizing 30292915Sdim/// cmpxchg. You'll want to make sure your target machine likes cmpxchg 31292915Sdim/// instructions in the first place and that there isn't another, better, 32292915Sdim/// transformation available (for example AArch32/AArch64 have linked loads). 33292915Sdim/// 34292915Sdim/// This is useful in passes which can't rewrite the more exotic RMW 35292915Sdim/// instructions directly into a platform specific intrinsics (because, say, 36292915Sdim/// those intrinsics don't exist). If such a pass is able to expand cmpxchg 37292915Sdim/// instructions directly however, then, with this function, it could avoid two 38292915Sdim/// extra module passes (avoiding passes by `-atomic-expand` and itself). A 39292915Sdim/// specific example would be PNaCl's `RewriteAtomics` pass. 40292915Sdim/// 41292915Sdim/// Given: atomicrmw some_op iN* %addr, iN %incr ordering 42292915Sdim/// 43292915Sdim/// The standard expansion we produce is: 44292915Sdim/// [...] 45292915Sdim/// %init_loaded = load atomic iN* %addr 46292915Sdim/// br label %loop 47292915Sdim/// loop: 48292915Sdim/// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ] 49292915Sdim/// %new = some_op iN %loaded, %incr 50321369Sdim/// ; This is what -atomic-expand will produce using this function on i686 51321369Sdim/// targets: 52292915Sdim/// %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val 53292915Sdim/// %new_loaded = extractvalue { iN, i1 } %pair, 0 54292915Sdim/// %success = extractvalue { iN, i1 } %pair, 1 55292915Sdim/// ; End callback produced IR 56292915Sdim/// br i1 %success, label %atomicrmw.end, label %loop 57292915Sdim/// atomicrmw.end: 58292915Sdim/// [...] 59292915Sdim/// 60292915Sdim/// Returns true if the containing function was modified. 61321369Sdimbool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun Factory); 62321369Sdim 63321369Sdim} // end namespace llvm 64321369Sdim 65321369Sdim#endif // LLVM_CODEGEN_ATOMICEXPANDUTILS_H 66