[gcc r14-9872] lto/114655 - -flto=4 at link time doesn't override -flto=auto at compile time

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:32fb04adae90a0ea68e64e8fc3cb04b613b2e9f3

commit r14-9872-g32fb04adae90a0ea68e64e8fc3cb04b613b2e9f3
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Apr 9 14:25:57 2024 +0200

    lto/114655 - -flto=4 at link time doesn't override -flto=auto at compile time
    
    The following adjusts -flto option processing in lto-wrapper to have
    link-time -flto override any compile time setting.
    
            PR lto/114655
            * lto-wrapper.cc (merge_flto_options): Add force argument.
            (merge_and_complain): Do not force here.
            (run_gcc): But here to make the link-time -flto option override
            any compile-time one.

Diff:
---
 gcc/lto-wrapper.cc | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/gcc/lto-wrapper.cc b/gcc/lto-wrapper.cc
index 610594cdc2b..02579951569 100644
--- a/gcc/lto-wrapper.cc
+++ b/gcc/lto-wrapper.cc
@@ -218,15 +218,18 @@ find_option (vec<cl_decoded_option> &options, cl_decoded_option *option)
   return find_option (options, option->opt_index);
 }
 
-/* Merge -flto FOPTION into vector of DECODED_OPTIONS.  */
+/* Merge -flto FOPTION into vector of DECODED_OPTIONS.  If FORCE is true
+   then FOPTION overrides previous settings.  */
 
 static void
 merge_flto_options (vec<cl_decoded_option> &decoded_options,
-		    cl_decoded_option *foption)
+		    cl_decoded_option *foption, bool force)
 {
   int existing_opt = find_option (decoded_options, foption);
   if (existing_opt == -1)
     decoded_options.safe_push (*foption);
+  else if (force)
+    decoded_options[existing_opt].arg = foption->arg;
   else
     {
       if (strcmp (foption->arg, decoded_options[existing_opt].arg) != 0)
@@ -493,7 +496,7 @@ merge_and_complain (vec<cl_decoded_option> &decoded_options,
 	  break;
 
 	case OPT_flto_:
-	  merge_flto_options (decoded_options, foption);
+	  merge_flto_options (decoded_options, foption, false);
 	  break;
 	}
     }
@@ -1550,8 +1553,8 @@ run_gcc (unsigned argc, char *argv[])
 	  break;
 
 	case OPT_flto_:
-	  /* Merge linker -flto= option with what we have in IL files.  */
-	  merge_flto_options (fdecoded_options, option);
+	  /* Override IL file settings with a linker -flto= option.  */
+	  merge_flto_options (fdecoded_options, option, true);
 	  if (strcmp (option->arg, "jobserver") == 0)
 	    jobserver_requested = true;
 	  break;