• ahaas's avatar
    [wasm] Introduce the TrapIf and TrapUnless operators to generate trap code. · 7bd61b60
    ahaas authored
    Some instructions in WebAssembly trap for some inputs, which means that the
    execution is terminated and (at least at the moment) a JavaScript exception is
    thrown. Examples for traps are out-of-bounds memory accesses, or integer
    divisions by zero.
    
    Without the TrapIf and TrapUnless operators trap check in WebAssembly introduces 5
    TurboFan nodes (branch, if_true, if_false, trap-reason constant, trap-position
    constant), in addition to the trap condition itself. Additionally, each
    WebAssembly function has four TurboFan nodes (merge, effect_phi, 2 phis) whose
    number of inputs is linear to the number of trap checks in the function.
    Especially for functions with high numbers of trap checks we observe a
    significant slowdown in compilation time, down to 0.22 MiB/s in the sqlite
    benchmark instead of the average of 3 MiB/s in other benchmarks. By introducing
    a TrapIf common operator only a single node is necessary per trap check, in
    addition to the trap condition. Also the nodes which are shared between trap
    checks (merge, effect_phi, 2 phis) would disappear. First measurements suggest a
    speedup of 30-50% on average.
    
    This CL only implements TrapIf and TrapUnless on x64. The implementation is also
    hidden behind the --wasm-trap-if flag.
    
    Please take a special look at how the source position is transfered from the
    instruction selector to the code generator, and at the context that is used for
    the runtime call.
    
    R=titzer@chromium.org
    
    Review-Url: https://codereview.chromium.org/2562393002
    Cr-Commit-Position: refs/heads/master@{#41720}
    7bd61b60
wasm-external-refs.h 1.83 KB