Following the discussion in bugzilla I have came to a conclusion that the
problem is that we copy REG_NOTEs along with the instructions. they belong
to. This is not correct for some kinds of REG_NOTE. The fix is to prevent
us from copying the notes in some of the cases. I have went over the notes
defined in reg-notes.def and listed below the notes that (IMO) copying them
maybe not correct. All the reg-notes that aren't mentioned below either
describe a side effect on the insn they belong to (so the note is correct
for the new copy) or they belong to call/jump instructions that we do not
copy. We use duplicate_insn_chain, which calls emit_copy_of_insn_after to
do the actual copy, the later copies the notes along with the instructions,
a possible fix is to pass this function a flag to tell her not to copy the
below mentioned kind of notes when the flag is specified and to act in the
normal way if not. What do you think ?
REG_NOTE (DEP_TRUE)
REG_NOTE (DEP_ANTI)
REG_NOTE (DEP_OUTPUT)
I suppose we shouldn't care about these because emit_copy_of_insn_after
doesn't copy LOG_LINKs.
REG_NOTE (DEAD)
musn't be copied (the cause of the bug)
REG_NOTE (NONNEG)
REG_NOTE (NO_CONFLICT)
REG_NOTE (UNUSED)
mustn't be copied
describe a fact about other instructions so this
may change if copied.
REG_NOTE (CC_SETTER)
REG_NOTE (CC_USER)
I suppose that using CC0 is possible only in branch instructions (correct
me if I am wrong)
and since (at least currently) we aren't copying the compare/branch so we
shouldn't
worry about it, I suppose that the correct handling for this (once we
need it)
is to copy the pair and update the link respectively.
