The main IRA routine includes the code: /* Don't move insns if live range shrinkage or register pressure-sensitive scheduling were done because it will not improve allocation but likely worsen insn scheduling. */ if (optimize && !flag_live_range_shrinkage && !(flag_sched_pressure && flag_schedule_insns)) combine_and_move_insns ();
The comment about not moving insns for pressure-sensitive scheduling makes sense, but I think the combine part of combine_and_move_insns is still useful, since it's folding a set of an equivalent value into its single user and so eliminates the need for one register altogether. (That also means that it's likely to undo live range shrinkage in some cases, so I think the blanket skip still makes sense there.) Tested on aarch64-linux-gnu, aarch64_be-elf and x86_64-linux-gnu. OK to install? Richard 2019-08-07 Richard Sandiford <richard.sandif...@arm.com> gcc/ * ira.c (combine_and_move_insns): Don't move insns if pressure-sensitive scheduling is enabled. (ira): Remove check for pressure-sensitive scheduling here. gcc/testsuite/ * gcc.target/aarch64/csinc-3.c: New test. * gcc.target/aarch64/csinv-2.c: Likewise. Index: gcc/ira.c =================================================================== --- gcc/ira.c 2019-07-10 19:41:27.159891908 +0100 +++ gcc/ira.c 2019-08-07 19:12:57.945375459 +0100 @@ -3748,6 +3748,11 @@ combine_and_move_insns (void) auto_bitmap cleared_regs; int max = max_reg_num (); + /* Don't move insns if register pressure-sensitive scheduling was + done because it will not improve allocation but likely worsen insn + scheduling. */ + bool allow_move_p = !(flag_sched_pressure && flag_schedule_insns); + for (int regno = FIRST_PSEUDO_REGISTER; regno < max; regno++) { if (!reg_equiv[regno].replace) @@ -3829,7 +3834,7 @@ combine_and_move_insns (void) /* Move the initialization of the register to just before USE_INSN. Update the flow information. */ - else if (prev_nondebug_insn (use_insn) != def_insn) + else if (allow_move_p && prev_nondebug_insn (use_insn) != def_insn) { rtx_insn *new_insn; @@ -5307,12 +5312,8 @@ ira (FILE *f) reg_equiv = XCNEWVEC (struct equivalence, max_reg_num ()); update_equiv_regs (); - /* Don't move insns if live range shrinkage or register - pressure-sensitive scheduling were done because it will not - improve allocation but likely worsen insn scheduling. */ - if (optimize - && !flag_live_range_shrinkage - && !(flag_sched_pressure && flag_schedule_insns)) + /* This subpass could undo the effects of live range shrinkage. */ + if (optimize && !flag_live_range_shrinkage) combine_and_move_insns (); /* Gather additional equivalences with memory. */ Index: gcc/testsuite/gcc.target/aarch64/csinc-3.c =================================================================== --- /dev/null 2019-07-30 08:53:31.317691683 +0100 +++ gcc/testsuite/gcc.target/aarch64/csinc-3.c 2019-08-07 19:12:57.945375459 +0100 @@ -0,0 +1,15 @@ +/* { dg-do compile } */ +/* { dg-options "-O2" } */ + +int +foo (int a, int b) +{ + if (a < 0) + return 1; + if (a == 0) + return b; + return b + 1; +} + +/* { dg-final { scan-assembler-not {\tmov\tw[0-9]+, 1\n} } } */ +/* { dg-final { scan-assembler {\tcsinc\tw[0-9]+, w[0-9]+, wzr, ge\n} } } */ Index: gcc/testsuite/gcc.target/aarch64/csinv-2.c =================================================================== --- /dev/null 2019-07-30 08:53:31.317691683 +0100 +++ gcc/testsuite/gcc.target/aarch64/csinv-2.c 2019-08-07 19:12:57.945375459 +0100 @@ -0,0 +1,15 @@ +/* { dg-do compile } */ +/* { dg-options "-O2" } */ + +int +foo (int a, int b) +{ + if (a < 0) + return -1; + if (a == 0) + return 0; + return 1; +} + +/* { dg-final { scan-assembler-not {\tmov\tw[0-9]+, -1\n} } } */ +/* { dg-final { scan-assembler {\tcsinv\tw[0-9]+, w[0-9]+, wzr, ge\n} } } */