`transf.handOffBody` is the seam between the two halves: rewriting ends, and
from there the reading side works off a cursor. `cgen.genProcLvl3` takes the
handoff once the body is final and runs `allPathsAsgnResult` — which has been
`AnyNode` since the predicates landed — over the CURSOR rather than the `PNode`.
Three things this had to get right, none of them obvious from the outside.
WHERE the handoff goes. A bridged buffer is a SNAPSHOT, so it has to be taken
after the last rewrite. Destructor injection runs after `transformBody` returns,
and `easyResultAsgn` sets `nfPreventCg` on the tree later still — a buffer taken
at the end of `transformBody` would describe a tree that no longer exists by the
time anything read it. So the API lives in `transf`, which owns that invariant,
and the call site is in `cgen`, which is where rewriting actually finishes. The
one flag `easyResultAsgn` writes afterwards is read only by the `PNode`
generator, and it sits in the branch that does not run the analysis at all.
WHY it is gated on `-d:newIcBackend`. `expr` cannot migrate a piece at a time:
it dispatches to ~60 emitters, so either all of them take `AnyNode` or the
dispatch converts at every node. Until that happens the generator still needs a
`PNode`, and building a buffer per routine in a default build would cost a tree
walk and buy nothing. The analyses are the part that moves now.
THAT IT IS ACTUALLY LOAD-BEARING. "Byte-identical output" is worth nothing if
the new path never ran, so: cursor-driven and `PNode`-driven builds produce
identical `.c` (50/50 on an 89k-line target, 12/12 on the grind target), and
forcing the cursor-driven answer wrong changes 10 of 12 files. The first number
alone would have been consistent with the code being dead.
Verified: grind clean (1431 bodies, 260_431 nodes, 0 disagreements, neither
tolerance taken); the default path is byte-identical to HEAD; all four build
configurations compile.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XEF7FJvUkGKvG9LSGuEaNR
e988e0366c