Having everybody and their uncle reading and writing fields out
of a.code and stubs.code was making assembler work hard. This replaces most
reads with accessors, and all writes with structured friends of
X64SAssembler.
Most of the SpillStacks we do are just to keep the in-memory VM stack
clean in case a helper call throws an exception. Many of these exceptions are
vanishingly rare, so let's stop making the fast path slower for them. This diff
adds support for catch traces, which are just like normal exit traces with one
major exception: they're never jumped to from translated code. If we're
unwinding a TC frame and discover that the current rip has a catch trace
registered, the unwinder will execute it before resuming unwinding.
The unwinder parts were fairly straightfoward, then I ran into a bunch of
issues with SetM. The SetElem instruction sometimes consumes a reference to one
of its inputs, which is bad news for our optimizations. To make everything work
again, I changed SetElem to throw an exception in cases where it would've
previously decreffed the value input. This is a special exception that the new
unwinding code recognizes. When one of these is caught, the catch trace
executed for that TC frame will finish up the vector instruction and push the
value provided by the exception on the stack. This allows us to optimize most
traces under the assumption that SetM's output is the same as its input,
letting the catch trace clean things up if the helper decides that's not the
case and throws.
There is one common case where SetM's output isn't the same as its input:
setting an offset in a string base returns a new String. Luckily, we can detect
most of these at compile time so SetElem returns a new StringData* when the
base is known to be a string. If the base might be a string, SetElem will
return nullptr if the base wasn't a string, and a StringData* if it was. We
test the output in these cases and side exit if the return value of SetElem is
non-null (I have yet to see this side exit happen outside of artificially
created test cases).
Once I got things working in the vector translator, I went through every other
call to spillStack and exceptionBarrier, replacing them with catch traces as
appropriate.
I was learning from @jdelong and he said that you should use
double quotes for local includes and angle brackets for library
includes. I asked why our code was the way it was, and he said he wanted
to clean it up. I beat him to it :)
Conflicts:
hphp/runtime/base/server/admin_request_handler.cpp
hphp/runtime/vm/named_entity.h
Include locals information in gdb via the preexisting dwarf output.
As discussed I have a top level DIE for 'HPHP::TypedValue' with the same name
which gdb takes care of while doing the opaque type resolution.
This change is mostly for FB internal organizational reasons.
Building is not effected beyond the fact that the target now
lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
Keith Adams