compilers: gnu: implement get_lto_link_args

Without this, we pass (say) `-flto=auto` at compile-time, but just `-flto`
at link-time.

See also https://gcc.gnu.org/PR114655 and the linked r12-824-g3cbcb5d0cfcd17,
i.e. before GCC 12, we'd end up linking with 1 job.

The clang mixin looks correct already.

Closes: https://github.com/mesonbuild/meson/issues/9536

1 files changed, 17 insertions, 1 deletions

diff --git a/mesonbuild/compilers/mixins/gnu.py b/mesonbuild/compilers/mixins/gnu.py
index 239d7ef3a..fa34bb4ca 100644
--- a/mesonbuild/compilers/mixins/gnu.py
+++ b/mesonbuild/compilers/mixins/gnu.py
@@ -623,7 +623,7 @@ class GnuCompiler(GnuLikeCompiler):
         if threads == 0:
             if self._has_lto_auto_support:
                 return ['-flto=auto']
-            # This matches clang's behavior of using the number of cpus, but
+            # This matches gcc's behavior of using the number of cpus, but
             # obeying meson's MESON_NUM_PROCESSES convention.
             return [f'-flto={mesonlib.determine_worker_count()}']
         elif threads > 0:
@@ -636,6 +636,22 @@ class GnuCompiler(GnuLikeCompiler):
             return ['-fuse-ld=mold']
         return super().use_linker_args(linker, version)
 
+    def get_lto_link_args(self, *, threads: int = 0, mode: str = 'default',
+                          thinlto_cache_dir: T.Optional[str] = None) -> T.List[str]:
+        args: T.List[str] = []
+        if threads == 0:
+            if self._has_lto_auto_support:
+                args.append('-flto=auto')
+            else:
+                # This matches gcc's behavior of using the number of cpus, but
+                # obeying meson's MESON_NUM_PROCESSES convention.
+                args.append(f'-flto={mesonlib.determine_worker_count()}')
+        elif threads > 0:
+            args.append(f'-flto={threads}')
+        else:
+            args.extend(super().get_lto_compile_args(threads=threads))
+        return args
+
     def get_profile_use_args(self) -> T.List[str]:
         return super().get_profile_use_args() + ['-fprofile-correction']