From: Vladimir N. Makarov <vmakarov@redhat.com>
Date: Mon, 13 May 2024 14:12:11 +0000 (-0400)
Subject: [PR115013][LRA]: Modify register starvation recognition
X-Git-Tag: basepoints/gcc-16~9117
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=r15-436-g44e7855e;p=thirdparty%2Fgcc.git

[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 --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index e945a4da451..92b343fa99a 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]))