Our SelectionDAG instruction selection mechanism prints out a very
detailed and useful trace with the -debug option. Conversely, with -O0
when fast isel is running, there is no equivalent output. Instead,
debugging has to rely on -fast-isel-verbose2 which just prints out
statistics at the end of the run and -fast-isel-abort to catch places
when selection aborted. But even simple tracing of which instructions
were matched with isel and where it bailed out (along with a simple
reason for bailing out - i.e. "target could not lower arguments")
could be very useful.
Are there any objections to adding such tracing capabilities?
Everything under DEBUG(), of course, just with the SelectionDAG -debug