¶bool expandAtomicRMWToCmpXchg(
    llvm::AtomicRMWInst* AI,
    llvm::CreateCmpXchgInstFun CreateCmpXchg)

Description

Expand an atomic RMW instruction into a loop utilizing cmpxchg. You'll want to make sure your target machine likes cmpxchg instructions in the first place and that there isn't another, better, transformation available (for example AArch32/AArch64 have linked loads). This is useful in passes which can't rewrite the more exotic RMW instructions directly into a platform specific intrinsics (because, say, those intrinsics don't exist). If such a pass is able to expand cmpxchg instructions directly however, then, with this function, it could avoid two extra module passes (avoiding passes by `-atomic-expand` and itself). A specific example would be PNaCl's `RewriteAtomics` pass. Given: atomicrmw some_op iN* %addr, iN %incr ordering The standard expansion we produce is: [...] %init_loaded = load atomic iN* %addr br label %loop loop: %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ] %new = some_op iN %loaded, %incr ; This is what -atomic-expand will produce using this function on i686 targets: %pair = cmpxchg iN* %addr, iN %loaded, iN %new_val %new_loaded = extractvalue { iN, i1 } %pair, 0 %success = extractvalue { iN, i1 } %pair, 1 ; End callback produced IR br i1 %success, label %atomicrmw.end, label %loop atomicrmw.end: [...] Returns true if the containing function was modified.

Declared at: llvm/include/llvm/CodeGen/AtomicExpandUtils.h:60

Parameters

llvm::AtomicRMWInst* AI

llvm::CreateCmpXchgInstFun CreateCmpXchg