1. 17 Aug, 2020 1 commit
    • 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