On 11/14/18 6:07 AM, Robin Dapp wrote: > This patch checks whether the current target supports conditional moves > with immediate then/else operands and allows noce_convert_multiple_sets > to deal with constants subsequently. > Also, minor refactoring is performed. > > -- > > gcc/ChangeLog: > > 2018-11-14 Robin Dapp <rd...@linux.ibm.com> > > * ifcvt.c (have_const_cmov): New function. > (noce_convert_multiple_sets): Allow constants if supported. > (bb_ok_for_noce_convert_multiple_sets): Likewise. > (check_cond_move_block): Refactor. > --- > gcc/ifcvt.c | 46 ++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 36 insertions(+), 10 deletions(-) > > diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c > index ddf077fa051..660bb46eb1c 100644 > --- a/gcc/ifcvt.c > +++ b/gcc/ifcvt.c > @@ -3077,6 +3077,27 @@ bb_valid_for_noce_process_p (basic_block test_bb, rtx > cond, > return false; > } > > +/* Check if we have a movcc pattern that accepts constants as then/else > + operand (op 2/3). */ > +static bool > +have_const_cmov (machine_mode mode) > +{ > + enum insn_code icode; > + if ((icode = direct_optab_handler (movcc_optab, mode)) > + != CODE_FOR_nothing) > + { > + if (insn_data[(int) icode].operand[2].predicate > + && (insn_data[(int) icode].operand[2].predicate > + (const1_rtx, insn_data[(int) icode].operand[2].mode))) > + if (insn_data[(int) icode].operand[3].predicate > + && (insn_data[(int) icode].operand[3].predicate > + (const1_rtx, insn_data[(int) icode].operand[3].mode))) > + return true; > + } > + > + return false; > +} This may ultimately be too simplistic. There are targets where some constants are OK, but others may not be. By checking the predicate like this I think you can cause over-aggressive if-conversion if the target allows a range of integers in the expander's operand predicate, but allows a narrower range in the actual define_insn (presumably the expander loads them into a pseudo or somesuch in that case).
We know that over-aggressive if-conversion into conditional moves hurts some targets. Ideally you'd create the actual insn with the constants you want to use and see if that's recognized as well as compute its cost. Is that just too painful at this point for some reason? > @@ -3689,7 +3717,7 @@ check_cond_move_block (basic_block bb, > { > rtx set, dest, src; > > - if (!NONDEBUG_INSN_P (insn) || JUMP_P (insn)) > + if (!active_insn_p (insn)) > continue; > set = single_set (insn); > if (!set) > @@ -3705,10 +3733,8 @@ check_cond_move_block (basic_block bb, > if (!CONSTANT_P (src) && !register_operand (src, VOIDmode)) > return FALSE; > > - if (side_effects_p (src) || side_effects_p (dest)) > - return FALSE; > - > - if (may_trap_p (src) || may_trap_p (dest)) > + /* Check for side effects and trapping. */ > + if (!noce_operand_ok (src) || !noce_operand_ok (dest)) > return FALSE; > > /* Don't try to handle this if the source register was These two hunks are probably OK as general cleanups. Note that noce_operand_ok is not strictly the same as checking side_effects_p and may_trap_p in the case of a MEM. But you've already filtered out MEMs before you get here. Jeff >