Fix usage of live in opcodes and no longer preserve registers by default

Many opcodes have a live parameter which is the number of registers that should
be preserved by GC operations. Take this into account and conversely stop
preserving registers by default.

This affects significantly the safety of `memory_ensure_free` when writing nifs.
Indeed, arguments (which come from registers) are no longer preserved.
However, no platform-specific nif was found that needed to be fixed. If
required, calls to `memory_ensure_free` or `memory_ensure_free_opt` should be
replaced with calls to `memory_ensure_free_with_roots`.

Signed-off-by: Paul Guyot <[email protected]>

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [0.6.0-beta.0] - Unreleased
 
+### Fixed
+
+- Fixed interpretation of live for opcodes, thus altering GC semantics for nifs. See also [UPDATING](UPDATING.md).
+
 ### Added
 - Added `esp:get_default_mac/0` for retrieving the default MAC address on ESP32.
 - Added support for `pico` and `poci` as an alternative to `mosi` and `miso` for SPI

UPDATING.md

@@ -6,6 +6,13 @@
 
 # AtomVM Update Instructions
 
+## v0.6.0-alpha.1 -> v0.6.0-beta.0
+
+- Registers are no longer preserved by GC by default when invoking nifs, as part of the fix
+of interpretation of the emulator of the live parameter of many opcodes. NIFs may need
+to call `memory_ensure_free_with_roots` and pass their arguments are roots, instead of
+`memory_ensure_free` or `memory_ensure_free_opt`.
+
 ## v0.6.0-alpha.0 -> v0.6.0-alpha.1
 
 - **Libraries (or boot .avm file) from latest version must be used**. Standard library from