When I submitted my previous lra-remat patch, I mentioned I had some 
concerns about the way we dealt with register number comparisons, but I 
didn't want to change things blindly without a testcase. PR70123 has now 
provided such a testcase where we are trying to rematerialize a hard 
register (r6). While scanning we encounter an instruction of the form
  (set (reg 285) (reg 272))
i.e. involving only pseudos, but reg_renumber[285] is r6. Since we only 
compare register numbers, we do not notice that the hard reg is clobbered.

The following patch modifies the function input_regno_present_p, and 
also renames it so that its purpose is more obvious to someone familiar 
with other parts of gcc. I've made it look at reg_renumber, and also try 
to deal with multi-word hard registers properly.

I'm not entirely sure this is a fully safe approach however, since I 
can't yet answer the question of whether LRA could change another pseudo 
to reside in hard register 6, thereby making the rematerialization 
invalid after the fact. Therefore the patch also includes a change to 
just disable candidates if they involve hard registers. I haven't 
observed that making any difference in code generation (on x86_64), 
beyond fixing the testcase on s390.

Bootstrapped and tested on x86_64-linux; Jakub verified that the 
testcase works afterwards. Ok for trunk and 5-branch, either for one or 
for both parts? I'm hoping the testcase in gcc.dg/torture will get 
exercised in the right way on s390, but I haven't run tests on that machine.


Bernd