[gcc r15-436] [PR115013][LRA]: Modify register starvation recognition

[Vladimir Makarov via Gcc-cvs]

https://gcc.gnu.org/g:44e7855e4e817a7f5a1e332cd95e780e57052dba

commit r15-436-g44e7855e4e817a7f5a1e332cd95e780e57052dba
Author: Vladimir N. Makarov <vmaka...@redhat.com>
Date:   Mon May 13 10:12:11 2024 -0400

    [PR115013][LRA]: Modify register starvation recognition
    
      My recent patch to recognize reg starvation resulted in few GCC test
    failures.  The following patch fixes this by using more accurate
    starvation calculation and ignoring small reg classes.
    
    gcc/ChangeLog:
    
            PR rtl-optimization/115013
            * lra-constraints.cc (process_alt_operands): Update all_used_nregs
            only for winreg.  Ignore reg starvation for small reg classes.

Diff:
---
 gcc/lra-constraints.cc | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index e945a4da4519..92b343fa99a0 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -2674,8 +2674,9 @@ process_alt_operands (int only_alternative)
              if (early_clobber_p
                  || curr_static_id->operand[nop].type != OP_OUT)
                {
-                 all_used_nregs
-                   += ira_reg_class_min_nregs[this_alternative][mode];
+                 if (winreg)
+                   all_used_nregs
+                     += ira_reg_class_min_nregs[this_alternative][mode];
                  all_this_alternative
                    = (reg_class_subunion
                       [all_this_alternative][this_alternative]);
@@ -3250,6 +3251,7 @@ process_alt_operands (int only_alternative)
          overall += LRA_MAX_REJECT;
        }
       if (all_this_alternative != NO_REGS
+         && !SMALL_REGISTER_CLASS_P (all_this_alternative)
          && all_used_nregs != 0 && all_reload_nregs != 0
          && (all_used_nregs + all_reload_nregs + 1
              >= ira_class_hard_regs_num[all_this_alternative]))