Bug 248481 – Alignment assumed by RegisterAtOffsetList does not accurately describe SIMD registers

• Status: RESOLVED
• Resolution: FIXED
• Component: WebAssembly

[David Degazio]

rdar://102515450

The current RegisterAtOffsetList implementation assumes that the alignment of a register's value is the same as the width of that register. However, 128-bit SIMD registers are currently only aligned to eight-byte intervals. This mismatch between RegisterAtOffsetList's size calculation and other locations (such as in RegisterSetBuilder) can cause assertion failure. For example:

    (module
      (type (;0;) (func (result i32 v128)))
      (func (;0;) (type 0) (result i32 v128)
        (local v128)
        i32.const 0
        v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000
      )
      (export "foo" (func 0))
    )

...results in:

    ASSERTION FAILED: static_cast<size_t>(offset - startOffset) == sizeOfAreaInBytes

[David Degazio]

Pull request: https://github.com/WebKit/WebKit/pull/6929

[EWS]

Committed 257192@main (f958a5f2b00b): <https://commits.webkit.org/257192@main>

Reviewed commits have been landed. Closing PR #6929 and removing active labels.