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65 lines
2.5 KiB
C++
65 lines
2.5 KiB
C++
//===- AtomicExpandUtils.h - Utilities for expanding atomic instructions --===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_ATOMICEXPANDUTILS_H
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#define LLVM_CODEGEN_ATOMICEXPANDUTILS_H
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/Support/AtomicOrdering.h"
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namespace llvm {
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class AtomicRMWInst;
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class Value;
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/// Parameters (see the expansion example below):
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/// (the builder, %addr, %loaded, %new_val, ordering,
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/// /* OUT */ %success, /* OUT */ %new_loaded)
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using CreateCmpXchgInstFun =
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function_ref<void(IRBuilder<> &, Value *, Value *, Value *, AtomicOrdering,
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Value *&, Value *&)>;
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/// Expand an atomic RMW instruction into a loop utilizing
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/// cmpxchg. You'll want to make sure your target machine likes cmpxchg
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/// instructions in the first place and that there isn't another, better,
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/// transformation available (for example AArch32/AArch64 have linked loads).
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///
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/// This is useful in passes which can't rewrite the more exotic RMW
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/// instructions directly into a platform specific intrinsics (because, say,
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/// those intrinsics don't exist). If such a pass is able to expand cmpxchg
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/// instructions directly however, then, with this function, it could avoid two
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/// extra module passes (avoiding passes by `-atomic-expand` and itself). A
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/// specific example would be PNaCl's `RewriteAtomics` pass.
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///
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/// Given: atomicrmw some_op iN* %addr, iN %incr ordering
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///
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/// The standard expansion we produce is:
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/// [...]
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/// %init_loaded = load atomic iN* %addr
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/// br label %loop
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/// loop:
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/// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ]
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/// %new = some_op iN %loaded, %incr
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/// ; This is what -atomic-expand will produce using this function on i686
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/// targets:
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/// %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val
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/// %new_loaded = extractvalue { iN, i1 } %pair, 0
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/// %success = extractvalue { iN, i1 } %pair, 1
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/// ; End callback produced IR
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/// br i1 %success, label %atomicrmw.end, label %loop
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/// atomicrmw.end:
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/// [...]
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///
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/// Returns true if the containing function was modified.
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bool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI, CreateCmpXchgInstFun CreateCmpXchg);
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} // end namespace llvm
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#endif // LLVM_CODEGEN_ATOMICEXPANDUTILS_H
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