>> I1 is def_insn, I3 is cand->insn. tmp_reg is 'ax'. What we want to do
>> is reject this transformation
>> because the destination of def_insn (aka I1), that is 'ax', is not the
>> operand of the extend operation
>> in cand->insn (aka I3). As you said, rtx_equal won't work on just
>> SET_SRC (PATTERN (cand->insn)) because
>> it's an extend operation. So reg_overlap_mentioned should be appropriate.

Yeah, so just use the src_reg variable for the comparison. I still don't 
see why you wouldn't want to use the stronger test. But the whole thing 
still feels not completely ideal somehow, so after reading through ree.c 
for a while and getting a better feeling for how it works, I think the 
following (which you said is equivalent) would be the most 
understandable and direct fix.

You said that the two tests should be equivalent, and I agree. I've not 
found cases where the change makes a difference, other than the 
testcase. Would you mind running this version through the testsuite and 
committing if it passes?

I've shrunk the comment; massive explanations like this for every bug 
are inappropriate IMO, and the example also duplicates an earlier 
comment in the same function. And, as I said earlier, the way you placed 
the comment is confusing because only one part of the following if 
statement is related to it.


Bernd