Rollup merge of #53950 - michaelwoerister:more-lto-cli, r=alexcrichton

Allow for opting out of ThinLTO and clean up LTO related cli flag handling.

It turns out that there currently is no way to explicitly disable ThinLTO (except for the nightly-only `-Zthinlto` flag). This PR extends `-C lto` to take `yes` and `no` in addition to `thin` and `fat`. It should be backwards compatible.

It also cleans up how LTO mode selection is handled.

Note that merging the PR in the current state would make the new values for `-C lto` available on the stable channel. I think that would be fine but maybe some team should vote on it.

4 files changed, 4 insertions, 8 deletions

diff --git a/src/librustc_codegen_llvm/back/link.rs b/src/librustc_codegen_llvm/back/link.rs
index d50a56ad84a..8248385c127 100644
--- a/src/librustc_codegen_llvm/back/link.rs
+++ b/src/librustc_codegen_llvm/back/link.rs
@@ -1666,7 +1666,6 @@ fn relevant_lib(sess: &Session, lib: &NativeLibrary) -> bool {
 
 fn are_upstream_rust_objects_already_included(sess: &Session) -> bool {
     match sess.lto() {
-        Lto::Yes |
         Lto::Fat => true,
         Lto::Thin => {
             // If we defer LTO to the linker, we haven't run LTO ourselves, so
diff --git a/src/librustc_codegen_llvm/back/linker.rs b/src/librustc_codegen_llvm/back/linker.rs
index ebb229b7b6b..95be2d82123 100644
--- a/src/librustc_codegen_llvm/back/linker.rs
+++ b/src/librustc_codegen_llvm/back/linker.rs
@@ -205,13 +205,12 @@ impl<'a> GccLinker<'a> {
         self.linker_arg(&format!("-plugin-opt={}", opt_level));
         self.linker_arg(&format!("-plugin-opt=mcpu={}", llvm_util::target_cpu(self.sess)));
 
-        match self.sess.opts.cg.lto {
+        match self.sess.lto() {
             config::Lto::Thin |
             config::Lto::ThinLocal => {
                 self.linker_arg("-plugin-opt=thin");
             }
             config::Lto::Fat |
-            config::Lto::Yes |
             config::Lto::No => {
                 // default to regular LTO
             }
diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs
index 25bc662c408..364b469738f 100644
--- a/src/librustc_codegen_llvm/back/lto.rs
+++ b/src/librustc_codegen_llvm/back/lto.rs
@@ -118,7 +118,7 @@ pub(crate) fn run(cgcx: &CodegenContext,
         Lto::ThinLocal => SymbolExportLevel::Rust,
 
         // We're doing LTO for the entire crate graph
-        Lto::Yes | Lto::Fat | Lto::Thin => {
+        Lto::Fat | Lto::Thin => {
             symbol_export::crates_export_threshold(&cgcx.crate_types)
         }
 
@@ -201,7 +201,6 @@ pub(crate) fn run(cgcx: &CodegenContext,
                                              .map(|c| c.as_ptr())
                                              .collect::<Vec<_>>();
     match cgcx.lto {
-        Lto::Yes | // `-C lto` == fat LTO by default
         Lto::Fat => {
             assert!(cached_modules.is_empty());
             let opt_jobs = fat_lto(cgcx,
diff --git a/src/librustc_codegen_llvm/back/write.rs b/src/librustc_codegen_llvm/back/write.rs
index 6b257ed4c3e..7b78d4fb4ff 100644
--- a/src/librustc_codegen_llvm/back/write.rs
+++ b/src/librustc_codegen_llvm/back/write.rs
@@ -937,7 +937,6 @@ fn need_pre_thin_lto_bitcode_for_incr_comp(sess: &Session) -> bool {
     }
 
     match sess.lto() {
-        Lto::Yes |
         Lto::Fat |
         Lto::No => false,
         Lto::Thin |
@@ -1372,7 +1371,7 @@ fn execute_optimize_work_item(cgcx: &CodegenContext,
         // require LTO so the request for LTO is always unconditionally
         // passed down to the backend, but we don't actually want to do
         // anything about it yet until we've got a final product.
-        Lto::Yes | Lto::Fat | Lto::Thin => {
+        Lto::Fat | Lto::Thin => {
             cgcx.crate_types.len() != 1 ||
                 cgcx.crate_types[0] != config::CrateType::Rlib
         }
@@ -1552,7 +1551,7 @@ fn start_executing_work(tcx: TyCtxt,
                 exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
                 Some(Arc::new(exported_symbols))
             }
-            Lto::Yes | Lto::Fat | Lto::Thin => {
+            Lto::Fat | Lto::Thin => {
                 exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
                 for &cnum in tcx.crates().iter() {
                     exported_symbols.insert(cnum, copy_symbols(cnum));