D746 - A compute dispatch binds each traced buffer and writes it back

Status: decided Date: 2026-10-05

A compute dispatch's buffers are traced as a draw's are (D733), stores included: every buffer a buffer_load_dword* or buffer_store_dword* reaches through a descriptor the dispatch's user data supplies gets a binding of its own, filled from the guest range the descriptor names and, after the dispatch, written back to guest memory where it changed - the same all-or-nothing write the window gets (D711). The window covers only the accesses left untraced. Two bound ranges that overlap each other or the window are refused, since separate copies of one byte would disagree. A program that writes any other way - a typed store, an atomic, a scratch store, a global store of part of a word (whole-word global stores bind as D961 says) - traces nothing and keeps the single window.

Why: the window is one power-of-two span of at most 64 Ki words, and a dispatch's buffers need not be near each other. radeonsi's buffer copy reads one buffer and writes another wherever its allocator put them: STKT00001's dispatch at 0xd04 copies four bytes from 0x40a600000 to 0x412012008, 128 MiB apart, and was refused.

Rejected:

• Several windows: each would carry the window's bounds and placement rules, which a bound buffer already replaces with the descriptor's own.
• Binding buffers read-only and storing through the window: a program that reads back what it stored would read the snapshot.