[gcc r14-60] rtl-optimization/109237 - speedup bb_is_just_return

[gcc r14-60] rtl-optimization/109237 - speedup bb_is_just_return

[Richard Biener]

https://gcc.gnu.org/g:8f81100115f68b37fb2723e987c14a3185d1f47d

commit r14-60-g8f81100115f68b37fb2723e987c14a3185d1f47d
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Mar 22 10:05:19 2023 +0100

    rtl-optimization/109237 - speedup bb_is_just_return
    
    For the testcase bb_is_just_return is on top of the profile, changing
    it to walk BB insns backwards puts it off the profile.  That's because
    in the forward walk you have to process possibly many debug insns
    but in a backward walk you very likely run into control insns first.
    
            PR rtl-optimization/109237
            * cfgcleanup.cc (bb_is_just_return): Walk insns backwards.

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

diff --git a/gcc/cfgcleanup.cc b/gcc/cfgcleanup.cc
index 194e0e5de12..78f59e99653 100644
--- a/gcc/cfgcleanup.cc
+++ b/gcc/cfgcleanup.cc
@@ -2608,14 +2608,14 @@ bb_is_just_return (basic_block bb, rtx_insn **ret, rtx_insn **use)
   if (bb == EXIT_BLOCK_PTR_FOR_FN (cfun))
     return false;
 
-  FOR_BB_INSNS (bb, insn)
+  FOR_BB_INSNS_REVERSE (bb, insn)
     if (NONDEBUG_INSN_P (insn))
       {
 	rtx pat = PATTERN (insn);
 
 	if (!*ret && ANY_RETURN_P (pat))
 	  *ret = insn;
-	else if (!*ret && !*use && GET_CODE (pat) == USE
+	else if (*ret && !*use && GET_CODE (pat) == USE
 	    && REG_P (XEXP (pat, 0))
 	    && REG_FUNCTION_VALUE_P (XEXP (pat, 0)))
 	  *use = insn;