http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48496
--- Comment #4 from Vladimir Makarov <vmakarov at redhat dot com> 2011-04-11
17:11:37 UTC ---
The new big IRA patch just triggered a latent reload bug.
The code in question is in function reload_as_needed
/* If this was an ASM, make sure that all the reload insns
we have generated are valid. If not, give an error
and delete them. */
if (asm_noperands (PATTERN (insn)) >= 0)
for (p = NEXT_INSN (prev); p != next; p = NEXT_INSN (p))
if (p != insn && INSN_P (p)
&& GET_CODE (PATTERN (p)) != USE
&& (recog_memoized (p) < 0
|| (extract_insn (p), ! constrain_operands (1))))
{
error_for_asm (insn,
"%<asm%> operand requires "
"impossible reload");
delete_insn (p);
}
}
A previous insn P has a spilled pseudo and that results in the error generation
because spilled pseudos are changed by memory later.
I guess the above code is wrong if a previous insn has a spilled pseudo.
The bug did not occur before the big IRA patch because the pseudo in question
happened not to be spilled. I should mention that it is more profitable to
spill the pseudo and the new IRA makes the right decision (which results in
live range shrinkage and decreasing register pressure).
I could make a patch (preventing the error generation if there are spilled
pseudos in insn P) but I think that reload maintainers would do that different
(e.g. moving the check after changing spilled pseudos by memory) or make a
better patch.
