Send -fno-lto when linker plugin LTO is not requested to avoid having GCC do LTO when using rustc_codegen_gcc

Author: antoyo

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -902,7 +902,14 @@ impl<'a> Linker for GccLinker<'a> {
     fn linker_plugin_lto(&mut self) {
         match self.sess.opts.cg.linker_plugin_lto {
             LinkerPluginLto::Disabled => {
-                // Nothing to do
+                // GCC, when used as a linker, will perform LTO even without -flto when it sees
+                // object files with the GCC IR (which can happen when using rustc_codegen_gcc).
+                // Since the std is compiled with -Cembed-bitcode=yes, any program using the std
+                // will have the linker do LTO.
+                // So, we disable this with -fno-lto when linker plugin LTO is not requested.
+                if self.is_cc() {
+                    self.cc_arg("-fno-lto");
+                }
             }
             LinkerPluginLto::LinkerPluginAuto => {
                 self.push_linker_plugin_lto_args(None);

tests/run-make/fno-lto/main.rs

@@ -0,0 +1 @@
+fn main() {}

tests/run-make/fno-lto/rmake.rs

@@ -0,0 +1,16 @@
+//@ needs-target-std
+//@ ignore-msvc
+//@ ignore-wasm
+
+use run_make_support::rustc;
+
+fn main() {
+    rustc().input("main.rs").print("link-args").run_unchecked().assert_stdout_contains("-fno-lto");
+
+    rustc()
+        .input("main.rs")
+        .arg("-Clinker-plugin-lto")
+        .print("link-args")
+        .run_unchecked()
+        .assert_stdout_not_contains("-fno-lto");
+}

tests/run-make/linker-warning/short-error.txt

@@ -1,6 +1,6 @@
 error: linking with `./fake-linker` failed: exit status: 1
   |
-  = note:  "./fake-linker" "-m64" "/symbols.o" "<2 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "/build-root/test/run-make/linker-warning/rmake_out/{libfoo,libbar}.rlib" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "/build-root/test/run-make/linker-warning/rmake_out" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "main" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs" "run_make_error"
+  = note:  "./fake-linker" "-m64" "/symbols.o" "<2 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "/build-root/test/run-make/linker-warning/rmake_out/{libfoo,libbar}.rlib" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-fno-lto" "-L" "/build-root/test/run-make/linker-warning/rmake_out" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "main" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs" "run_make_error"
   = note: some arguments are omitted. use `--verbose` to show all linker arguments
   = note: error: baz