Correct rationale in simd_x86_64.S comment #72

Merged
andrew merged 1 commits from weaselbot/conflict-set:weaselbot/issue-71 into main 2026-08-03 04:59:28 +00:00
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// SIMD operations on potentially-indeterminate Node16::index[16] bytes. // SIMD operations on potentially-indeterminate Node16::index[16] bytes.
// Written in assembly so msan doesn't track the loads. The caller is // Written in assembly because loading and operating on indeterminate values
// responsible for masking the returned bitfield to [0, numChildren) before // is UB in C++ but well-defined in assembly. (A side effect is that msan
// using it. // doesn't track the loads.) The caller is responsible for masking the
// returned bitfield to [0, numChildren) before using it.
// //
// All functions return a 16-bit bitmask in %eax (bit i set = condition true // All functions return a 16-bit bitmask in %eax (bit i set = condition true
// at index i). The upper 16 bits of %eax are zero. // at index i). The upper 16 bits of %eax are zero.