llvm: dwo only emitted when object code emitted

`CompiledModule` should not think a DWARF object was emitted when a
bitcode-only compilation has happened, this can confuse archive file
creation (which expects to create an archive containing non-existent dwo
files).

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -765,11 +765,21 @@ pub(crate) unsafe fn codegen(
         drop(handlers);
     }
 
+    // `.dwo` files are only emitted if:
+    //
+    // - Object files are being emitted (i.e. bitcode only or metadata only compilations will not
+    //   produce dwarf objects, even if otherwise enabled)
+    // - Target supports Split DWARF
+    // - Split debuginfo is enabled
+    // - Split DWARF kind is `split` (i.e. debuginfo is split into `.dwo` files, not different
+    //   sections in the `.o` files).
+    let dwarf_object_emitted = matches!(config.emit_obj, EmitObj::ObjectCode(_))
+        && cgcx.target_can_use_split_dwarf
+        && cgcx.split_debuginfo != SplitDebuginfo::Off
+        && cgcx.split_dwarf_kind == SplitDwarfKind::Split;
     Ok(module.into_compiled_module(
         config.emit_obj != EmitObj::None,
-        cgcx.target_can_use_split_dwarf
-            && cgcx.split_debuginfo != SplitDebuginfo::Off
-            && cgcx.split_dwarf_kind == SplitDwarfKind::Split,
+        dwarf_object_emitted,
         config.emit_bc,
         &cgcx.output_filenames,
     ))

src/test/run-make-fulldeps/split-debuginfo/Makefile

@@ -53,7 +53,7 @@ off:
 	[ ! -f $(TMPDIR)/*.dwp ]
 	[ ! -f $(TMPDIR)/*.dwo ]
 
-packed: packed-split packed-single packed-remapped packed-crosscrate
+packed: packed-split packed-single packed-lto packed-remapped packed-crosscrate
 
 # - Debuginfo in `.dwo` files
 # - `.o` deleted
@@ -77,6 +77,32 @@ packed-single:
 	rm $(TMPDIR)/foo.dwp
 	rm $(TMPDIR)/$(call BIN,foo)
 
+packed-lto: packed-lto-split packed-lto-single
+
+# - rmeta file added to rlib, no object files are generated and thus no debuginfo is generated
+# - `.o` never created
+# - `.dwo` never created
+# - `.dwp` never created
+packed-lto-split:
+	$(RUSTC) baz.rs -g $(UNSTABLEOPTS) -Csplit-debuginfo=packed -Zsplit-dwarf-kind=split \
+		--crate-type=rlib -Clinker-plugin-lto
+	ls $(TMPDIR)/*.o && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwo && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwp && exit 1 || exit 0
+	rm $(TMPDIR)/libbaz.rlib
+
+# - rmeta file added to rlib, no object files are generated and thus no debuginfo is generated
+# - `.o` never created
+# - `.dwo` never created
+# - `.dwp` never created
+packed-lto-single:
+	$(RUSTC) baz.rs -g $(UNSTABLEOPTS) -Csplit-debuginfo=packed -Zsplit-dwarf-kind=single \
+		--crate-type=rlib -Clinker-plugin-lto
+	ls $(TMPDIR)/*.o && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwo && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwp && exit 1 || exit 0
+	rm $(TMPDIR)/libbaz.rlib
+
 packed-remapped: packed-remapped-split packed-remapped-single
 
 # - Debuginfo in `.dwo` files
@@ -153,7 +179,7 @@ packed-crosscrate-single:
 	rm $(TMPDIR)/main.dwp
 	rm $(TMPDIR)/$(call BIN,main)
 
-unpacked: unpacked-split unpacked-single unpacked-remapped unpacked-crosscrate
+unpacked: unpacked-split unpacked-single unpacked-lto unpacked-remapped unpacked-crosscrate
 
 # - Debuginfo in `.dwo` files
 # - `.o` deleted
@@ -177,6 +203,32 @@ unpacked-single:
 	ls $(TMPDIR)/*.dwp && exit 1 || exit 0
 	rm $(TMPDIR)/$(call BIN,foo)
 
+unpacked-lto: packed-lto-split packed-lto-single
+
+# - rmeta file added to rlib, no object files are generated and thus no debuginfo is generated
+# - `.o` never created
+# - `.dwo` never created
+# - `.dwp` never created
+unpacked-lto-split:
+	$(RUSTC) baz.rs -g $(UNSTABLEOPTS) -Csplit-debuginfo=unpacked -Zsplit-dwarf-kind=split \
+		--crate-type=rlib -Clinker-plugin-lto
+	ls $(TMPDIR)/*.o && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwo && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwp && exit 1 || exit 0
+	rm $(TMPDIR)/libbaz.rlib
+
+# - rmeta file added to rlib, no object files are generated and thus no debuginfo is generated
+# - `.o` never created
+# - `.dwo` never created
+# - `.dwp` never created
+unpacked-lto-single:
+	$(RUSTC) baz.rs -g $(UNSTABLEOPTS) -Csplit-debuginfo=unpacked -Zsplit-dwarf-kind=single \
+		--crate-type=rlib -Clinker-plugin-lto
+	ls $(TMPDIR)/*.o && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwo && exit 1 || exit 0
+	ls $(TMPDIR)/*.dwp && exit 1 || exit 0
+	rm $(TMPDIR)/libbaz.rlib
+
 unpacked-remapped: unpacked-remapped-split unpacked-remapped-single
 
 # - Debuginfo in `.dwo` files

src/test/run-make-fulldeps/split-debuginfo/baz.rs

@@ -0,0 +1 @@
+// empty