[gcc 11 backport] Support ld.mold linker.

[gcc 11 backport] Support ld.mold linker.

[Romain Geissler]

Hi,

Is it ok to backport small unrisky features to the old gcc 11 branch ?
Here is a proposal to merge the ld.mold linker support which Martin has
pushed in gcc >= 12. It's a cherry-pick of commit
ad964f7eaef9c03ce68a01cfdd7fde9d56524868. Note that it doesn't backport
the gcc build machinery to be able to link gcc itself with mold.

Note: it also doesn't backport Martin's change in the LTO machinery to
support LTO plugin with mold.

Cheers,
Romain


gcc/ChangeLog:

	* collect2.c (main): Add ld.mold.
	* common.opt: Add -fuse-ld=mold.
	* doc/invoke.texi: Document it.
	* gcc.c (driver_handle_option): Handle -fuse-ld=mold.
	* opts.c (common_handle_option): Likewise.
---
 gcc/collect2.c      | 10 +++++++---
 gcc/common.opt      |  4 ++++
 gcc/doc/invoke.texi |  4 ++++
 gcc/gcc.c           |  4 ++++
 gcc/opts.c          |  1 +
 5 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/gcc/collect2.c b/gcc/collect2.c
index 3e212fc75f3..558016af486 100644
--- a/gcc/collect2.c
+++ b/gcc/collect2.c
@@ -785,6 +785,7 @@ main (int argc, char **argv)
       USE_GOLD_LD,
       USE_BFD_LD,
       USE_LLD_LD,
+      USE_MOLD_LD,
       USE_LD_MAX
     } selected_linker = USE_DEFAULT_LD;
   static const char *const ld_suffixes[USE_LD_MAX] =
@@ -793,7 +794,8 @@ main (int argc, char **argv)
       PLUGIN_LD_SUFFIX,
       "ld.gold",
       "ld.bfd",
-      "ld.lld"
+      "ld.lld",
+      "ld.mold"
     };
   static const char *const real_ld_suffix = "real-ld";
   static const char *const collect_ld_suffix = "collect-ld";
@@ -970,6 +972,8 @@ main (int argc, char **argv)
 	  selected_linker = USE_GOLD_LD;
 	else if (strcmp (argv[i], "-fuse-ld=lld") == 0)
 	  selected_linker = USE_LLD_LD;
+	else if (strcmp (argv[i], "-fuse-ld=mold") == 0)
+	  selected_linker = USE_MOLD_LD;
 	else if (strncmp (argv[i], "-o", 2) == 0)
 	  {
 	    /* Parse the output filename if it's given so that we can make
@@ -1082,7 +1086,7 @@ main (int argc, char **argv)
   ld_file_name = 0;
 #ifdef DEFAULT_LINKER
   if (selected_linker == USE_BFD_LD || selected_linker == USE_GOLD_LD ||
-      selected_linker == USE_LLD_LD)
+      selected_linker == USE_LLD_LD || selected_linker == USE_MOLD_LD)
     {
       char *linker_name;
 # ifdef HOST_EXECUTABLE_SUFFIX
@@ -1317,7 +1321,7 @@ main (int argc, char **argv)
 	      else if (!use_collect_ld
 		       && strncmp (arg, "-fuse-ld=", 9) == 0)
 		{
-		  /* Do not pass -fuse-ld={bfd|gold|lld} to the linker. */
+		  /* Do not pass -fuse-ld={bfd|gold|lld|mold} to the linker. */
 		  ld1--;
 		  ld2--;
 		}
diff --git a/gcc/common.opt b/gcc/common.opt
index 4a3f09d9e1f..b7f0a52348c 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2967,6 +2967,10 @@ fuse-ld=lld
 Common Driver Negative(fuse-ld=lld)
 Use the lld LLVM linker instead of the default linker.
 
+fuse-ld=mold
+Common Driver Negative(fuse-ld=mold)
+Use the Modern linker (MOLD) linker instead of the default linker.
+
 fuse-linker-plugin
 Common Undocumented Var(flag_use_linker_plugin)
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index fffa899585e..3ecdb850000 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -15606,6 +15606,10 @@ Use the @command{gold} linker instead of the default linker.
 @opindex fuse-ld=lld
 Use the LLVM @command{lld} linker instead of the default linker.
 
+@item -fuse-ld=mold
+@opindex fuse-ld=mold
+Use the Modern Linker (@command{mold}) instead of the default linker.
+
 @cindex Libraries
 @item -l@var{library}
 @itemx -l @var{library}
diff --git a/gcc/gcc.c b/gcc/gcc.c
index 20a649ea08e..ecda8cbba02 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -4196,6 +4196,10 @@ driver_handle_option (struct gcc_options *opts,
        use_ld = ".gold";
        break;
 
+    case OPT_fuse_ld_mold:
+       use_ld = ".mold";
+       break;
+
     case OPT_fcompare_debug_second:
       compare_debug_second = 1;
       break;
diff --git a/gcc/opts.c b/gcc/opts.c
index 24bb64198c8..9192ca75743 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2875,6 +2875,7 @@ common_handle_option (struct gcc_options *opts,
     case OPT_fuse_ld_bfd:
     case OPT_fuse_ld_gold:
     case OPT_fuse_ld_lld:
+    case OPT_fuse_ld_mold:
     case OPT_fuse_linker_plugin:
       /* No-op. Used by the driver and passed to us because it starts with f.*/
       break;
-- 
2.39.3