Vladimir Makarov <[email protected]> writes: > On 2019-06-21 9:43 a.m., Richard Sandiford wrote: >> make_early_clobber_and_input_conflicts records allocno conflicts >> between inputs and earlyclobber outputs. It (rightly) avoids >> doing this for inputs that are explicitly allowed to match the >> output due to matching constraints. >> >> The problem is that whether this matching is allowed varies >> between alternatives. At the moment the code avoids adding >> a clobber if *any* enabled alternative allows the match, >> even if some other operand makes that alternative impossible. >> >> The specific instance of this for SVE is that some alternatives >> allow matched earlyclobbers when a third operand X is constant zero. >> We should avoid adding conflicts when X really is constant zero, >> but should ignore the match if X is nonzero or nonconstant. >> >> ira_setup_alts can already filter these alternatives out for us, >> so all we need to do is use it in process_bb_node_lives. The >> preferred_alternatives variable is only used for this earlyclobber >> detection, so no other check should be affected. >> >> With the previous patch to check the reject weight in ira_setup_alts, >> this has the effect of ignoring expensive alternatives if we have >> other valid alternatives with zero cost. It seems reasonable to base >> the heuristic on only the alternatives that we'd actually like to use, >> but if this ends up being too aggressive, we could instead make the new >> reject behaviour conditional and only use it for add_insn_allocno_copies. >> > This patch definitely improves the heuristics. > > The only missed part is a comment for preferred_alternatives > > /* The value of get_preferred_alternatives for the current instruction, > supplemental to recog_data. */ > static alternative_mask preferred_alternatives; > > The comment becomes misleading after the patch.
Oops, thanks for noticing that. > With changing the comment, the patch is ok for me. Thanks, here's what I installed after testing on aarch64-linux-gnu and x86_64-linux-gnu. Richard 2019-07-01 Richard Sandiford <[email protected]> gcc/ * ira-lives.c (process_bb_node_lives): Use ira_setup_alts. Index: gcc/ira-lives.c =================================================================== --- gcc/ira-lives.c 2019-06-29 17:20:49.000000000 +0100 +++ gcc/ira-lives.c 2019-07-01 09:33:14.026477923 +0100 @@ -80,8 +80,9 @@ Software Foundation; either version 3, o /* The number of last call at which given allocno was saved. */ static int *allocno_saved_at_call; -/* The value of get_preferred_alternatives for the current instruction, - supplemental to recog_data. */ +/* The value returned by ira_setup_alts for the current instruction; + i.e. the set of alternatives that we should consider to be likely + candidates during reloading. */ static alternative_mask preferred_alternatives; /* If non-NULL, the source operand of a register to register copy for which @@ -1236,9 +1237,7 @@ process_bb_node_lives (ira_loop_tree_nod } } - extract_insn (insn); - preferred_alternatives = get_preferred_alternatives (insn); - preprocess_constraints (insn); + preferred_alternatives = ira_setup_alts (insn); process_single_reg_class_operands (false, freq); if (call_p)
