Teach stack promotion to walk the CFG when a potential reuse of an allocation is found to see if it can actually happen instead of just assuming it will. This allows it to catch cases like {{{ int i; Foo f; while (cond(i)) f = new Foo(i++); return f.value; }}} where it previously wouldn't because a phi using the allocation would appear in the condition block to propagate it to the use after the loop.

[Environment] 
DFLAGS=-I@RUNTIME_DIR@ -I@RUNTIME_DIR@/lib/common -L-L%@P%/../lib -d-version=Tango -defaultlib=@RUNTIME_AIO@ -debuglib=@RUNTIME_AIO@