Allow for opting out of ThinLTO and clean up LTO related cli flag han…

…dling.

src/librustc/session/config.rs

@@ -68,15 +68,13 @@ pub enum OptLevel {
     SizeMin,    // -Oz
 }
 
+/// This is what the `LtoCli` values get mapped to after resolving defaults and
+/// and taking other command line options into account.
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum Lto {
     /// Don't do any LTO whatsoever
     No,
 
-    /// Do a full crate graph LTO. The flavor is determined by the compiler
-    /// (currently the default is "fat").
-    Yes,
-
     /// Do a full crate graph LTO with ThinLTO
     Thin,
 
@@ -88,6 +86,23 @@ pub enum Lto {
     Fat,
 }
 
+/// The different settings that the `-C lto` flag can have.
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum LtoCli {
+    /// `-C lto=no`
+    No,
+    /// `-C lto=yes`
+    Yes,
+    /// `-C lto`
+    NoParam,
+    /// `-C lto=thin`
+    Thin,
+    /// `-C lto=fat`
+    Fat,
+    /// No `-C lto` flag passed
+    Unspecified,
+}
+
 #[derive(Clone, PartialEq, Hash)]
 pub enum CrossLangLto {
     LinkerPlugin(PathBuf),
@@ -801,15 +816,16 @@ macro_rules! options {
         pub const parse_unpretty: Option<&'static str> =
             Some("`string` or `string=string`");
         pub const parse_lto: Option<&'static str> =
-            Some("one of `thin`, `fat`, or omitted");
+            Some("either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, \
+                  `fat`, or omitted");
         pub const parse_cross_lang_lto: Option<&'static str> =
             Some("either a boolean (`yes`, `no`, `on`, `off`, etc), \
                   or the path to the linker plugin");
     }
 
     #[allow(dead_code)]
     mod $mod_set {
-        use super::{$struct_name, Passes, Sanitizer, Lto, CrossLangLto};
+        use super::{$struct_name, Passes, Sanitizer, LtoCli, CrossLangLto};
         use rustc_target::spec::{LinkerFlavor, PanicStrategy, RelroLevel};
         use std::path::PathBuf;
 
@@ -1002,11 +1018,23 @@ macro_rules! options {
             }
         }
 
-        fn parse_lto(slot: &mut Lto, v: Option<&str>) -> bool {
+        fn parse_lto(slot: &mut LtoCli, v: Option<&str>) -> bool {
+            if v.is_some() {
+                let mut bool_arg = None;
+                if parse_opt_bool(&mut bool_arg, v) {
+                    *slot = if bool_arg.unwrap() {
+                        LtoCli::Yes
+                    } else {
+                        LtoCli::No
+                    };
+                    return true
+                }
+            }
+
             *slot = match v {
-                None => Lto::Yes,
-                Some("thin") => Lto::Thin,
-                Some("fat") => Lto::Fat,
+                None => LtoCli::NoParam,
+                Some("thin") => LtoCli::Thin,
+                Some("fat") => LtoCli::Fat,
                 Some(_) => return false,
             };
             true
@@ -1047,7 +1075,7 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
         "extra arguments to append to the linker invocation (space separated)"),
     link_dead_code: bool = (false, parse_bool, [UNTRACKED],
         "don't let linker strip dead code (turning it on can be used for code coverage)"),
-    lto: Lto = (Lto::No, parse_lto, [TRACKED],
+    lto: LtoCli = (LtoCli::Unspecified, parse_lto, [TRACKED],
         "perform LLVM link-time optimizations"),
     target_cpu: Option<String> = (None, parse_opt_string, [TRACKED],
         "select target processor (rustc --print target-cpus for details)"),
@@ -2373,8 +2401,8 @@ mod dep_tracking {
     use std::hash::Hash;
     use std::path::PathBuf;
     use std::collections::hash_map::DefaultHasher;
-    use super::{CrateType, DebugInfo, ErrorOutputType, Lto, OptLevel, OutputTypes,
-                Passes, Sanitizer, CrossLangLto};
+    use super::{CrateType, DebugInfo, ErrorOutputType, OptLevel, OutputTypes,
+                Passes, Sanitizer, LtoCli, CrossLangLto};
     use syntax::feature_gate::UnstableFeatures;
     use rustc_target::spec::{PanicStrategy, RelroLevel, TargetTriple};
     use syntax::edition::Edition;
@@ -2429,7 +2457,7 @@ mod dep_tracking {
     impl_dep_tracking_hash_via_hash!(RelroLevel);
     impl_dep_tracking_hash_via_hash!(Passes);
     impl_dep_tracking_hash_via_hash!(OptLevel);
-    impl_dep_tracking_hash_via_hash!(Lto);
+    impl_dep_tracking_hash_via_hash!(LtoCli);
     impl_dep_tracking_hash_via_hash!(DebugInfo);
     impl_dep_tracking_hash_via_hash!(UnstableFeatures);
     impl_dep_tracking_hash_via_hash!(OutputTypes);
@@ -2503,7 +2531,7 @@ mod tests {
     use lint;
     use middle::cstore;
     use session::config::{build_configuration, build_session_options_and_crate_config};
-    use session::config::{Lto, CrossLangLto};
+    use session::config::{LtoCli, CrossLangLto};
     use session::build_session;
     use std::collections::{BTreeMap, BTreeSet};
     use std::iter::FromIterator;
@@ -2937,7 +2965,7 @@ mod tests {
 
         // Make sure changing a [TRACKED] option changes the hash
         opts = reference.clone();
-        opts.cg.lto = Lto::Fat;
+        opts.cg.lto = LtoCli::Fat;
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
         opts = reference.clone();

src/librustc/session/mod.rs

@@ -547,9 +547,27 @@ impl Session {
         // lto` and we've for whatever reason forced off ThinLTO via the CLI,
         // then ensure we can't use a ThinLTO.
         match self.opts.cg.lto {
-            config::Lto::No => {}
-            config::Lto::Yes if self.opts.cli_forced_thinlto_off => return config::Lto::Fat,
-            other => return other,
+            config::LtoCli::Unspecified => {
+                // The compiler was invoked without the `-Clto` flag. Fall
+                // through to the default handling
+            }
+            config::LtoCli::No => {
+                // The user explicitly opted out of any kind of LTO
+                return config::Lto::No;
+            }
+            config::LtoCli::Yes |
+            config::LtoCli::Fat |
+            config::LtoCli::NoParam => {
+                // All of these mean fat LTO
+                return config::Lto::Fat;
+            }
+            config::LtoCli::Thin => {
+                return if self.opts.cli_forced_thinlto_off {
+                    config::Lto::Fat
+                } else {
+                    config::Lto::Thin
+                };
+            }
         }
 
         // Ok at this point the target doesn't require anything and the user
@@ -1174,7 +1192,6 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
 
     if sess.opts.incremental.is_some() {
         match sess.lto() {
-            Lto::Yes |
             Lto::Thin |
             Lto::Fat => {
                 sess.err("can't perform LTO when compiling incrementally");

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

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
             }

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,

src/librustc_codegen_llvm/back/write.rs

@@ -928,7 +928,6 @@ fn need_pre_thin_lto_bitcode_for_incr_comp(sess: &Session) -> bool {
     }
 
     match sess.lto() {
-        Lto::Yes |
         Lto::Fat |
         Lto::No => false,
         Lto::Thin |
@@ -1363,7 +1362,7 @@ 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
         }
@@ -1543,7 +1542,7 @@ 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));

src/test/run-make-fulldeps/codegen-options-parsing/Makefile

@@ -16,11 +16,11 @@ all:
 	$(RUSTC) -C extra-filename=foo dummy.rs 2>&1
 	#Option taking no argument
 	$(RUSTC) -C lto= dummy.rs 2>&1 | \
-		$(CGREP) 'codegen option `lto` - one of `thin`, `fat`, or'
+		$(CGREP) 'codegen option `lto` - either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted'
 	$(RUSTC) -C lto=1 dummy.rs 2>&1 | \
-		$(CGREP) 'codegen option `lto` - one of `thin`, `fat`, or'
+		$(CGREP) 'codegen option `lto` - either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted'
 	$(RUSTC) -C lto=foo dummy.rs 2>&1 | \
-		$(CGREP) 'codegen option `lto` - one of `thin`, `fat`, or'
+		$(CGREP) 'codegen option `lto` - either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted'
 	$(RUSTC) -C lto dummy.rs
 
 	# Should not link dead code...

src/test/run-make-fulldeps/lto-smoke/Makefile

@@ -1,6 +1,30 @@
 -include ../tools.mk
 
-all:
+all: noparam bool_true bool_false thin fat
+
+noparam:
 	$(RUSTC) lib.rs
 	$(RUSTC) main.rs -C lto
 	$(call RUN,main)
+
+bool_true:
+	$(RUSTC) lib.rs
+	$(RUSTC) main.rs -C lto=yes
+	$(call RUN,main)
+
+
+bool_false:
+	$(RUSTC) lib.rs
+	$(RUSTC) main.rs -C lto=off
+	$(call RUN,main)
+
+thin:
+	$(RUSTC) lib.rs
+	$(RUSTC) main.rs -C lto=thin
+	$(call RUN,main)
+
+fat:
+	$(RUSTC) lib.rs
+	$(RUSTC) main.rs -C lto=fat
+	$(call RUN,main)
+