rustc: add ability to output regular LTO bitcode modules

Adding the option to control from rustc CLI
if the resulted ".o" bitcode module files are with
thinLTO info or regular LTO info.

Allows using "-lto-embed-bitcode=optimized" during linkage
correctly.

Signed-off-by: Ziv Dunkelman <[email protected]>

Author: darkness-ai

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -199,7 +199,7 @@ pub(crate) fn run_thin(
 
 pub(crate) fn prepare_thin(module: ModuleCodegen<ModuleLlvm>) -> (String, ThinBuffer) {
     let name = module.name.clone();
-    let buffer = ThinBuffer::new(module.module_llvm.llmod());
+    let buffer = ThinBuffer::new(module.module_llvm.llmod(), true);
     (name, buffer)
 }
 
@@ -709,9 +709,9 @@ unsafe impl Send for ThinBuffer {}
 unsafe impl Sync for ThinBuffer {}
 
 impl ThinBuffer {
-    pub fn new(m: &llvm::Module) -> ThinBuffer {
+    pub fn new(m: &llvm::Module, is_thin: bool) -> ThinBuffer {
         unsafe {
-            let buffer = llvm::LLVMRustThinLTOBufferCreate(m);
+            let buffer = llvm::LLVMRustThinLTOBufferCreate(m, is_thin);
             ThinBuffer(buffer)
         }
     }

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -790,7 +790,7 @@ pub(crate) unsafe fn codegen(
             let _timer = cgcx
                 .prof
                 .generic_activity_with_arg("LLVM_module_codegen_make_bitcode", &*module.name);
-            let thin = ThinBuffer::new(llmod);
+            let thin = ThinBuffer::new(llmod, config.emit_thin_lto);
             let data = thin.data();
 
             if let Some(bitcode_filename) = bc_out.file_name() {

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2469,7 +2469,7 @@ extern "C" {
     pub fn LLVMRustModuleBufferFree(p: &'static mut ModuleBuffer);
     pub fn LLVMRustModuleCost(M: &Module) -> u64;
 
-    pub fn LLVMRustThinLTOBufferCreate(M: &Module) -> &'static mut ThinLTOBuffer;
+    pub fn LLVMRustThinLTOBufferCreate(M: &Module, is_thin: bool) -> &'static mut ThinLTOBuffer;
     pub fn LLVMRustThinLTOBufferFree(M: &'static mut ThinLTOBuffer);
     pub fn LLVMRustThinLTOBufferPtr(M: &ThinLTOBuffer) -> *const c_char;
     pub fn LLVMRustThinLTOBufferLen(M: &ThinLTOBuffer) -> size_t;

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -99,6 +99,7 @@ pub struct ModuleConfig {
     pub emit_ir: bool,
     pub emit_asm: bool,
     pub emit_obj: EmitObj,
+    pub emit_thin_lto: bool,
     pub bc_cmdline: String,
 
     // Miscellaneous flags.  These are mostly copied from command-line
@@ -218,6 +219,7 @@ impl ModuleConfig {
                 false
             ),
             emit_obj,
+            emit_thin_lto: sess.opts.unstable_opts.emit_thin_lto,
             bc_cmdline: sess.target.bitcode_llvm_cmdline.to_string(),
 
             verify_llvm_ir: sess.verify_llvm_ir(),

compiler/rustc_interface/src/tests.rs

@@ -734,6 +734,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(drop_tracking, true);
     tracked!(dual_proc_macros, true);
     tracked!(dwarf_version, Some(5));
+    tracked!(emit_thin_lto, false);
     tracked!(fewer_names, Some(true));
     tracked!(force_unstable_if_unmarked, true);
     tracked!(fuel, Some(("abc".to_string(), 99)));

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -34,6 +34,7 @@
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
 #include "llvm/LTO/LTO.h"
+#include "llvm/Bitcode/BitcodeWriterPass.h"
 #include "llvm-c/Transforms/PassManagerBuilder.h"
 
 #include "llvm/Transforms/Instrumentation.h"
@@ -1638,13 +1639,17 @@ struct LLVMRustThinLTOBuffer {
 };
 
 extern "C" LLVMRustThinLTOBuffer*
-LLVMRustThinLTOBufferCreate(LLVMModuleRef M) {
+LLVMRustThinLTOBufferCreate(LLVMModuleRef M, bool is_thin) {
   auto Ret = std::make_unique<LLVMRustThinLTOBuffer>();
   {
     raw_string_ostream OS(Ret->data);
     {
       legacy::PassManager PM;
-      PM.add(createWriteThinLTOBitcodePass(OS));
+      if (is_thin) {
+        PM.add(createWriteThinLTOBitcodePass(OS));
+      } else {
+        PM.add(createBitcodeWriterPass(OS));
+      }
       PM.run(*unwrap(M));
     }
   }

compiler/rustc_session/src/options.rs

@@ -1277,6 +1277,8 @@ options! {
         "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
     emit_stack_sizes: bool = (false, parse_bool, [UNTRACKED],
         "emit a section containing stack size metadata (default: no)"),
+    emit_thin_lto: bool = (true, parse_bool, [TRACKED],
+        "emit the bc module with thin LTO info (default: yes)"),
     fewer_names: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) \
         (default: no)"),

src/test/run-make-fulldeps/issue-84395-lto-embed-bitcode/Makefile

@@ -0,0 +1,11 @@
+# needs-matching-clang
+
+# This test makes sure the embed bitcode in elf created with
+# lto-embed-bitcode=optimized is valid llvm BC module.
+
+-include ../../run-make-fulldeps/tools.mk
+
+all:
+	$(RUSTC) test.rs --target $(TARGET) -Clink-arg=-fuse-ld=lld -Clinker-plugin-lto -Clinker=$(CLANG) -Clink-arg=-Wl,--plugin-opt=-lto-embed-bitcode=optimized -Zemit-thin-lto=no
+	$(LLVM_BIN_DIR)/objcopy --dump-section .llvmbc=$(TMPDIR)/test.bc $(TMPDIR)/test
+	$(LLVM_BIN_DIR)/llvm-dis $(TMPDIR)/test.bc

src/test/run-make-fulldeps/issue-84395-lto-embed-bitcode/test.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello World!");
+}

src/test/rustdoc-ui/z-help.stdout

@@ -35,6 +35,7 @@
     -Z                       dump-mir-spanview=val -- in addition to `.mir` files, create `.html` files to view spans for all `statement`s (including terminators), only `terminator` spans, or computed `block` spans (one span encompassing a block's terminator and all statements). If `-Z instrument-coverage` is also enabled, create an additional `.html` file showing the computed coverage spans.
     -Z                           dwarf-version=val -- version of DWARF debug information to emit (default: 2 or 4, depending on platform)
     -Z                        emit-stack-sizes=val -- emit a section containing stack size metadata (default: no)
+    -Z                           emit-thin-lto=val -- emit the bc module with thin LTO info (default: yes)
     -Z                             fewer-names=val -- reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) (default: no)
     -Z              force-unstable-if-unmarked=val -- force all crates to be `rustc_private` unstable (default: no)
     -Z                                    fuel=val -- set the optimization fuel quota for a crate