llvm/CodeGen/AtomicExpandUtils.h

0001 //===- AtomicExpandUtils.h - Utilities for expanding atomic instructions --===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef LLVM_CODEGEN_ATOMICEXPANDUTILS_H
0010 #define LLVM_CODEGEN_ATOMICEXPANDUTILS_H
0011
0012 #include "llvm/ADT/STLExtras.h"
0013 #include "llvm/IR/IRBuilder.h"
0014 #include "llvm/Support/AtomicOrdering.h"
0015
0016 namespace llvm {
0017
0018 class AtomicRMWInst;
0019 class Value;
0020
0021 /// Parameters (see the expansion example below):
0022 /// (the builder, %addr, %loaded, %new_val, ordering,
0023 ///  /* OUT */ %success, /* OUT */ %new_loaded,
0024 /// %MetadataSrc)
0025 using CreateCmpXchgInstFun = function_ref<void(
0026     IRBuilderBase &, Value *, Value *, Value *, Align, AtomicOrdering,
0027     SyncScope::ID, Value *&, Value *&, Instruction *)>;
0028
0029 /// Expand an atomic RMW instruction into a loop utilizing
0030 /// cmpxchg. You'll want to make sure your target machine likes cmpxchg
0031 /// instructions in the first place and that there isn't another, better,
0032 /// transformation available (for example AArch32/AArch64 have linked loads).
0033 ///
0034 /// This is useful in passes which can't rewrite the more exotic RMW
0035 /// instructions directly into a platform specific intrinsics (because, say,
0036 /// those intrinsics don't exist). If such a pass is able to expand cmpxchg
0037 /// instructions directly however, then, with this function, it could avoid two
0038 /// extra module passes (avoiding passes by `-atomic-expand` and itself). A
0039 /// specific example would be PNaCl's `RewriteAtomics` pass.
0040 ///
0041 /// Given: atomicrmw some_op iN* %addr, iN %incr ordering
0042 ///
0043 /// The standard expansion we produce is:
0044 ///     [...]
0045 ///     %init_loaded = load atomic iN* %addr
0046 ///     br label %loop
0047 /// loop:
0048 ///     %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ]
0049 ///     %new = some_op iN %loaded, %incr
0050 /// ; This is what -atomic-expand will produce using this function on i686
0051 /// targets:
0052 ///     %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val
0053 ///     %new_loaded = extractvalue { iN, i1 } %pair, 0
0054 ///     %success = extractvalue { iN, i1 } %pair, 1
0055 /// ; End callback produced IR
0056 ///     br i1 %success, label %atomicrmw.end, label %loop
0057 /// atomicrmw.end:
0058 ///     [...]
0059 ///
0060 /// Returns true if the containing function was modified.
0061 bool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun CreateCmpXchg);
0062
0063 } // end namespace llvm
0064
0065 #endif // LLVM_CODEGEN_ATOMICEXPANDUTILS_H