Rollup merge of rust-lang#63352 - jgalenson:reproducible-lto, r=alexc…

…richton

Sort the fat LTO modules to produce deterministic output.

Some projects that use LTO for their release builds are not reproducible.  We can fix this by sorting the fat LTO modules before using them.

It might also be useful to do this for thin LTO, but I couldn't get that to work to test it so I didn't do it.

src/librustc_codegen_llvm/back/lto.rs

@@ -265,7 +265,7 @@ fn fat_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
         // and we want to move everything to the same LLVM context. Currently the
         // way we know of to do that is to serialize them to a string and them parse
         // them later. Not great but hey, that's why it's "fat" LTO, right?
-        serialized_modules.extend(modules.into_iter().map(|module| {
+        let mut new_modules = modules.into_iter().map(|module| {
             match module {
                 FatLTOInput::InMemory(module) => {
                     let buffer = ModuleBuffer::new(module.module_llvm.llmod());
@@ -277,7 +277,10 @@ fn fat_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
                     (SerializedModule::Local(buffer), llmod_id)
                 }
             }
-        }));
+        }).collect::<Vec<_>>();
+        // Sort the modules to ensure we produce deterministic results.
+        new_modules.sort_by(|module1, module2| module1.1.partial_cmp(&module2.1).unwrap());
+        serialized_modules.extend(new_modules);
         serialized_modules.extend(cached_modules.into_iter().map(|(buffer, wp)| {
             (buffer, CString::new(wp.cgu_name).unwrap())
         }));

src/test/run-make-fulldeps/reproducible-build/Makefile

@@ -10,7 +10,8 @@ all:  \
 	link_paths \
 	remap_paths \
 	different_source_dirs \
-	extern_flags
+	extern_flags \
+	fat_lto
 
 smoke:
 	rm -rf $(TMPDIR) && mkdir $(TMPDIR)
@@ -76,3 +77,11 @@ extern_flags:
 		--extern reproducible_build_aux=$(TMPDIR)/libbar.rlib \
 		--crate-type rlib
 	cmp "$(TMPDIR)/libreproducible_build.rlib" "$(TMPDIR)/libfoo.rlib" || exit 1
+
+fat_lto:
+	rm -rf $(TMPDIR) && mkdir $(TMPDIR)
+	$(RUSTC) reproducible-build-aux.rs
+	$(RUSTC) reproducible-build.rs -C lto=fat -C opt-level=1
+	cp $(TMPDIR)/reproducible-build $(TMPDIR)/reproducible-build-a
+	$(RUSTC) reproducible-build.rs -C lto=fat -C opt-level=1
+	cmp "$(TMPDIR)/reproducible-build-a" "$(TMPDIR)/reproducible-build" || exit 1