[Joey-Magnus]

One of OoT's vertex programs (65dd5ce0adbe3b64) fails to translate ("native program uses lowering scratch registers") at an R2UR that reads R238. Nothing in it uses a scratch register: the lowering assumes R2UR's source may be a register pair.

Cause. R2UR UR6, R238 (ee0673c2 00000000 000e0000 000e2200). With the uniform bank in use, R238 is a high GPR. FieldSpan has no entry for R2UR, so the source's span came from its alignment: an even register, R4n+2, is taken as a pair, R238-R239. R239 is the lowering's own scratch, and R2UR lowers to eight words that use it, so that's a conflict. R2UR reads one 32-bit register.

Change (lower_to_maxwell.h, FieldSpan): R2UR's source spans one register, as MUFU's and CS2R's entries do for theirs.

Tests

• New tests/test_lower_r2ur_one_register.py: R2UR UR6, R238 is refused on main and lowers here; R236 lowers either way.
• run_all.py: all pass except nx2/test_nup_stand_in.py, red on main (fixed by test(nup): the stand-in test's stub takes the progress #1764 passes (main is red) #1790).
• I lowered a dump of the program's native code (kept on my PC, not in the PR): it now lowers. In game (Linux, RTX 4070 Ti, 595.99.02), stacked on fix(shaders): lower TLD.MS (multisampled texel fetch) to Maxwell TLDS 2D.LZ.MS #1769/fix(shaders): LDG/STG [URn+imm] with ordering bit 78 lower (2 compute programs) #1778/fix(shaders): ISBERD.O, a task program reading back its payload (12 failing pipelines) #1789/fix(shaders): two large compute programs lower (an immediate is not R254) and get their local memory #1800: programs that do not lower 2 → 1, the startup build's failed programs 3 → 2.

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[Joey-Magnus]

Thanks, you're right about R236: it's 4-aligned, so main took it for the quad R236-R239 and refused it too. The test now calls it a second case this fixes, and checks that R2UR UR6, R239 is still refused (R239 itself is the scratch). Rebased onto main (the run_all.py conflict); run_all.py passes apart from nx2/test_nup_stand_in.py, which #1790 fixes.