Add explicit conversions between forward and reverse ilist iterators.
These follow the conversion conventions of std::reverse_iterator, which
are off-by-one: the newly-constructed "reverse" iterator dereferences to
the previous node of the one sent in. This has the benefit of
converting reverse ranges in place:
- If [I, E) is a valid range,
- then [reverse(E), reverse(I)) gives the same range in reverse order.
ilist_iterator::getReverse() is unchanged: it returns a reverse iterator
to the *same* node.
llvm-svn: 294349
Now that MachineBasicBlock::reverse_instr_iterator knows when it's at
the end (since r281168 and r281170), implement
MachineBasicBlock::reverse_iterator directly on top of an
ilist::reverse_iterator by adding an IsReverse template parameter to
MachineInstrBundleIterator. This replaces another hard-to-reason-about
use of std::reverse_iterator on list iterators, matching the changes for
ilist::reverse_iterator from r280032 (see the "out of scope" section at
the end of that commit message). MachineBasicBlock::reverse_iterator
now has a handle to the current node and has obvious invalidation
semantics.
r280032 has a more detailed explanation of how list-style reverse
iterators (invalidated when the pointed-at node is deleted) are
different from vector-style reverse iterators like std::reverse_iterator
(invalidated on every operation). A great motivating example is this
commit's changes to lib/CodeGen/DeadMachineInstructionElim.cpp.
Note: If your out-of-tree backend deletes instructions while iterating
on a MachineBasicBlock::reverse_iterator or converts between
MachineBasicBlock::iterator and MachineBasicBlock::reverse_iterator,
you'll need to update your code in similar ways to r280032. The
following table might help:
[Old] ==> [New]
delete &*RI, RE = end() delete &*RI++
RI->erase(), RE = end() RI++->erase()
reverse_iterator(I) std::prev(I).getReverse()
reverse_iterator(I) ++I.getReverse()
--reverse_iterator(I) I.getReverse()
reverse_iterator(std::next(I)) I.getReverse()
RI.base() std::prev(RI).getReverse()
RI.base() ++RI.getReverse()
--RI.base() RI.getReverse()
std::next(RI).base() RI.getReverse()
(For more details, have a look at r280032.)
llvm-svn: 281172
Add an assertion to the MachineInstrBundleIterator from instr_iterator
that the underlying iterator is valid. This is possible know that we
can check ilist_node::isSentinel (since r281168), and is consistent with
the constructors from MachineInstr* and MachineInstr&.
Avoiding the new assertion in operator== and operator!= requires four
(!!!!) new overloads each.
(As an aside, I'm strongly in favour of:
- making the conversion from instr_iterator explicit;
- making the conversion from pointer explicit;
- making the conversion from reference explicit; and
- removing all the extra overloads of operator== and operator!= except
const_instr_iterator.
I'm not signing up for that at this point, but being clear about when
something is an MachineInstr-iterator (possibly instr_end()) vs
MachineInstr-bundle-iterator (possibly end()) vs MachineInstr* (possibly
nullptr) vs MachineInstr& (known valid) would surely make code
cleaner... and it would remove a ton of boilerplate from
MachineInstrBundleIterator operators.)
llvm-svn: 281170
This is a prep commit before fixing MachineBasicBlock::reverse_iterator
invalidation semantics, ala r281167 for ilist::reverse_iterator. This
changes MachineBasicBlock::Instructions to track which node is the
sentinel regardless of LLVM_ENABLE_ABI_BREAKING_CHECKS.
There's almost no functionality change (aside from ABI). However, in
the rare configuration:
#if !defined(NDEBUG) && !defined(LLVM_ENABLE_ABI_BREAKING_CHECKS)
the isKnownSentinel() assertions in ilist_iterator<>::operator* suddenly
have teeth for MachineInstr. If these assertions start firing for your
out-of-tree backend, have a look at the suggestions in the commit
message for r279314, and at some of the commits leading up to it that
avoid dereferencing the end() iterator.
llvm-svn: 281168
Remove all ilist_iterator to pointer casts. There were two reasons for
casts:
- Checking for an uninitialized (i.e., null) iterator. I added
MachineInstrBundleIterator::isValid() to check for that case.
- Comparing an iterator against the underlying pointer value while
avoiding converting the pointer value to an iterator. This is
occasionally necessary in MachineInstrBundleIterator, since there is
an assertion in the constructors that the underlying MachineInstr is
not bundled (but we don't care about that if we're just checking for
pointer equality).
To support the latter case, I rewrote the == and != operators for
ilist_iterator and MachineInstrBundleIterator.
- The implicit constructors now use enable_if to exclude
const-iterator => non-const-iterator conversions from overload
resolution (previously it was a compiler error on instantiation, now
it's SFINAE).
- The == and != operators are now global (friends), and are not
templated.
- MachineInstrBundleIterator has overloads to compare against both
const_pointer and const_reference. This avoids the implicit
conversions to MachineInstrBundleIterator that assert, instead just
checking the address (and I added unit tests to confirm this).
Notably, the only remaining uses of ilist_iterator::getNodePtrUnchecked
are in ilist.h, and no code outside of ilist*.h directly relies on this
UB end-iterator-to-pointer conversion anymore. It's still needed for
ilist_*sentinel_traits, but I'll clean that up soon.
llvm-svn: 278478
Duncan P. N. Exon Smith