[gcc r17-160] [IRA]: Fix implicit preference calculation.

[Vladimir Makarov]

https://gcc.gnu.org/g:9eb8a18033a473b30559862b3ff6a1cac162759b

commit r17-160-g9eb8a18033a473b30559862b3ff6a1cac162759b
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Tue Apr 28 08:36:13 2026 -0400

    [IRA]: Fix implicit preference calculation.
    
    When searching prefered hard regs from too strict constraints we can ignore
    some alternatives for subsequent operands.  This can result in worse code
    generation.  The patch fixes this.
    
    gcc/ChangeLog:
    
            * ira-lives.cc (ira_implicitly_set_insn_hard_regs): Use the same
            start prefered for all operand.

Diff:
---
 gcc/ira-lives.cc | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/gcc/ira-lives.cc b/gcc/ira-lives.cc
index 04e586343c82..a6b3eff1ab86 100644
--- a/gcc/ira-lives.cc
+++ b/gcc/ira-lives.cc
@@ -956,12 +956,14 @@ ira_implicitly_set_insn_hard_regs (HARD_REG_SET *set,
 	  mode = (GET_CODE (op) == SCRATCH
 		  ? GET_MODE (op) : PSEUDO_REGNO_MODE (regno));
 	  cl = NO_REGS;
-	  for (; (c = *p); p += CONSTRAINT_LEN (c, p))
+	  for (alternative_mask curr_preferred = preferred;
+	       (c = *p);
+	       p += CONSTRAINT_LEN (c, p))
 	    if (c == '#')
-	      preferred &= ~ALTERNATIVE_BIT (0);
+	      curr_preferred &= ~ALTERNATIVE_BIT (0);
 	    else if (c == ',')
-	      preferred >>= 1;
-	    else if (preferred & 1)
+	      curr_preferred >>= 1;
+	    else if (curr_preferred & 1)
 	      {
 		cl = reg_class_for_constraint (lookup_constraint (p));
 		if (cl != NO_REGS)