shader: drop the slots of a failed handle subtree with its code

When BuildHandleProgram failed on a subtree it truncated the code back to where
the subtree started, which removed the Tee ops of the values the subtree had
kept, but their entries stayed in g_handle_slots. A Phi tries its other inputs
after the first one fails; if one of them reused a value from the dropped
subtree, it emitted a Load of a slot that nothing wrote, so the handle read 0.

Number slots with a counter instead of counting map entries, and on failure
erase the entries numbered from the subtree's first slot on and rewind the
counter, so such a value is built again.

Follow-up to 561f87abec.

Assisted-by: Claude Sonnet 5.5 (implementation and commit message)

0 files changed, 0 insertions, 0 deletions