> Attached is a different fix. It splits DF_REF_IN_NOTE in two: One flag > for each kind of note. This allows the dead note removal code to > distinguish the source note for the EQ_USES. I needed to remove one > flag to keep the df_ref_flags 16-bit, but the DF_REF_SUBREG flag looks > completely unnecessary to me, and only ira.c uses it, so it wasn't to > hard to scavenge a single bit.
I'll defer this to Paolo. > The patch also includes all places I've found so far where the > compiler could create self-referencing notes: > > 1. optabs.c: Not sure what it was trying to do, but now it just > refuses to add a note if TARGET is mentioned in one of the source > operands. OK. > 2. gcse.c: gcse_emit_move_after added notes, but none of them was very > useful as far as I could tell, and almost all of them turned > self-referencing after CPROP. So I propose we just never add notes in > this case. gcse_emit_move_after also preserves existing notes. Are they problematic? > 3. cprop.c: It seems to me that the purpose here is to propagate > constants. If a reg could not be propagated, then the REG_EQUAL note > will not help much either. Propagating constants via REG_EQUAL notes > still helps folding comparisons sometimes, so I'm proposing we only > propagate those. As a bonus: less garbage RTL because a > cprop_constant_p can be shared. That seems a bit radical to me, especially in try_replace_reg which is used for copy propagation as well. In cprop_jump, why is attaching a note to the jump problematic? > 4. fwprop.c: If the SET_DEST is a REG that is mentioned in the > SET_SRC, don' create a note. This one I'm not very happy with, because > it doesn't handle the case that the REG is somehow simplified out of > the SET_SRC, but being smarter about this would only complicate > things. I for one can't think of anything better for the moment, > anyway. OK. > Finally, it makes sense to compute the NOTE problem for CSE. Why? It only uses REG_EQ* notes, so it seems like we're back to the earlier trick of using df_note_add_problem to clean up pre-existing REG_EQ* notes. -- Eric Botcazou
