• Ng Zhi An's avatar
    [wasm-simd] Support returning Simd128 on caller's stack · 360c9294
    Ng Zhi An authored
    In Liftoff, we were missing kS128 cases to load to/from stack.
    
    For the x64 and ARM64 instruction selector, the calculation of
    reverse_slot is incorrect for 128-bit values:
    
    - reverse_slot += 2 (size of 128-bit values, 2 pointers)
    - this copies from slot -2 into register
    - but the value starts at slot -1, it occupies slots -1 and -2
    - we end up copying slot -2 (most significant half) of the register, and
    also slot -3, which is where rsi was store (Wasm instance addr)
    - the test ends up with a different result every time
    
    The calculation of reverse_slot is changed to follow how ia32 and ARM
    does it, which is to start with
    
    - reverse_slot = 0
    - in the code-generator, add 1 to the slot
    - then after emitting Peek operation, reverse_slot += 2
    
    The fixes for x64 and ARM64 are in both instruction-selector and
    code-generator.
    
    ia32 and ARM didn't support writing kSimd128 values yet, it was only a
    missing check in code-generator, so add that in.
    
    For ARM, the codegen is more involved, vld1 does not support addressing
    with an offset, so we have to do the addition into a scratch register.
    
    Also adding a test for returning multiple v128. V128 is not exposed to
    JavaScript, so we use a Wasm function call, and then an involved chain
    of extract lanes, returning 6 i32 which we verify the values of. It
    extracts the first and last lane of the i32x4 value in order to catch
    bugs where we write or read to a wrong stack slot (off by 1).
    
    The simd-scalar-lowering for kCall was only handling single s128 return,
    we adopt the way i64-lowering handles kCall, so that is can now handle
    any kinds of calls with s128 in the descriptor.
    
    Bug: v8:10794
    Bug: chromium:1115230
    Change-Id: I2ccdd55f6292bc5794be78053b27e14da8cce70e
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2355189
    Commit-Queue: Zhi An Ng <zhin@chromium.org>
    Reviewed-by: 's avatarAndreas Haas <ahaas@chromium.org>
    Reviewed-by: 's avatarBill Budge <bbudge@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#69439}
    360c9294
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