When debugging code built with panic=about, the debug trace buffer is
not flushed on a panic and important messages are lost.
This does slow down debug tracing a bit, but this is still better than
unbuffered or line buffered I/O since the dbg!() macro can write out
many lines like a whole function.
The dbg!() macro should behave like a function call in how it evaluates
its arguments, and captures by Rust closures are not fully compatible
with path-specific borrowing. Specifically:
let borrow = &mut obj.foo;
dbg!("{}", obj.bar);
would fail because the closure inside dbg!() would borrow all of obj
instead of just obj.foo.
Fix this by using the format_args!() macro to evaluate the dbg!()
arguments and produce an fmt::Arguments object which can be safely
passed to the thread-local closure for printing.
The arguments are still evaluated inside an if { .. } which
constant-folds away in release builds.
Coalescing means creating virtual registers and transforming the code
into conventional SSA form. This means that every value used as a branch
argument will belong to the same virtual register as the corresponding
EBB argument value.
Conventional SSA form makes it easy to avoid memory-memory copies when
spilling values, and the virtual registers can be used as hints when
picking registers too. This reduces the number of register moves needed
for EBB arguments.
When the CRETONNE_DBG environment variable is set, send debug messages
to a file named cretonne.dbg.*.
The trace facility is only enabled when debug assertions are on.
