Gballet asked (comment 3099953085) to leave the sha256Sum256 / constant
parallelHashDepth optimisation out of this PR: it's an orthogonal
microbenchmark concern that should be revisited post-group-depth under
Go 1.26.
- Delete the sha256Sum256 helper from hasher.go.
- Delete the const parallelHashDepth = 4 from hasher.go.
- Restore master's dynamic parallelDepth() helper in store_commit.go
(copy verbatim — min(bits.Len(NumCPU), 8)).
- In hashInternal's shallow-parallel branch, call sha256.Sum256 directly
(std-lib, stack-allocated [32]byte; common.Hash is a type alias for
[32]byte so no conversion needed).
- In hashInternal's deep-sequential branch, use the pooled newSha256 /
returnSha256 hasher (matches master's internal_node.go:170-185).
Intentional trade-off: the deep branch now re-introduces per-hash
sync.Pool Get/Put plus a 32-byte h.Sum(nil) allocation. Zero regression
vs master; foregoes the arena's proposed stack-based hashing until
Go 1.26 + post-group-depth benchmarks.
3885e539b7