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