[gcc r14-2164] tree-optimization/110434 - avoid <retval> ={v} {CLOBBER} from NRV

[Richard Biener]

https://gcc.gnu.org/g:4bf76b5b6db8e68755788ec91012c5a686440720

commit r14-2164-g4bf76b5b6db8e68755788ec91012c5a686440720
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jun 28 11:27:45 2023 +0200

    tree-optimization/110434 - avoid <retval> ={v} {CLOBBER} from NRV
    
    When NRV replaces a local variable with <retval> it also replaces
    occurences in clobbers.  This leads to <retval> being clobbered
    before the return of it which is strictly invalid but harmless in
    practice since there's no pass after NRV which would remove
    earlier stores.
    
    The following fixes this nevertheless.
    
            PR tree-optimization/110434
            * tree-nrv.cc (pass_nrv::execute): Remove CLOBBERs of
            VAR we replace with <retval>.

Diff:
---
 gcc/tree-nrv.cc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/tree-nrv.cc b/gcc/tree-nrv.cc
index ff47439647c..99c4e21a842 100644
--- a/gcc/tree-nrv.cc
+++ b/gcc/tree-nrv.cc
@@ -264,7 +264,17 @@ pass_nrv::execute (function *fun)
 	      data.modified = 0;
 	      walk_gimple_op (stmt, finalize_nrv_r, &wi);
 	      if (data.modified)
-		update_stmt (stmt);
+		{
+		  /* If this is a CLOBBER of VAR, remove it.  */
+		  if (gimple_clobber_p (stmt))
+		    {
+		      unlink_stmt_vdef (stmt);
+		      gsi_remove (&gsi, true);
+		      release_defs (stmt);
+		      continue;
+		    }
+		  update_stmt (stmt);
+		}
 	      gsi_next (&gsi);
 	    }
 	}