1 //===- AtomicExpandUtils.h - Utilities for expanding atomic instructions --===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #ifndef LLVM_CODEGEN_ATOMICEXPANDUTILS_H 10 #define LLVM_CODEGEN_ATOMICEXPANDUTILS_H 11 12 #include "llvm/ADT/STLExtras.h" 13 #include "llvm/IR/IRBuilder.h" 14 #include "llvm/Support/AtomicOrdering.h" 15 16 namespace llvm { 17 18 class AtomicRMWInst; 19 class Value; 20 21 /// Parameters (see the expansion example below): 22 /// (the builder, %addr, %loaded, %new_val, ordering, 23 /// /* OUT */ %success, /* OUT */ %new_loaded) 24 using CreateCmpXchgInstFun = 25 function_ref<void(IRBuilder<> &, Value *, Value *, Value *, AtomicOrdering, 26 Value *&, Value *&)>; 27 28 /// Expand an atomic RMW instruction into a loop utilizing 29 /// cmpxchg. You'll want to make sure your target machine likes cmpxchg 30 /// instructions in the first place and that there isn't another, better, 31 /// transformation available (for example AArch32/AArch64 have linked loads). 32 /// 33 /// This is useful in passes which can't rewrite the more exotic RMW 34 /// instructions directly into a platform specific intrinsics (because, say, 35 /// those intrinsics don't exist). If such a pass is able to expand cmpxchg 36 /// instructions directly however, then, with this function, it could avoid two 37 /// extra module passes (avoiding passes by `-atomic-expand` and itself). A 38 /// specific example would be PNaCl's `RewriteAtomics` pass. 39 /// 40 /// Given: atomicrmw some_op iN* %addr, iN %incr ordering 41 /// 42 /// The standard expansion we produce is: 43 /// [...] 44 /// %init_loaded = load atomic iN* %addr 45 /// br label %loop 46 /// loop: 47 /// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ] 48 /// %new = some_op iN %loaded, %incr 49 /// ; This is what -atomic-expand will produce using this function on i686 50 /// targets: 51 /// %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val 52 /// %new_loaded = extractvalue { iN, i1 } %pair, 0 53 /// %success = extractvalue { iN, i1 } %pair, 1 54 /// ; End callback produced IR 55 /// br i1 %success, label %atomicrmw.end, label %loop 56 /// atomicrmw.end: 57 /// [...] 58 /// 59 /// Returns true if the containing function was modified. 60 bool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun CreateCmpXchg); 61 62 } // end namespace llvm 63 64 #endif // LLVM_CODEGEN_ATOMICEXPANDUTILS_H 65