From bdd66b3f98e8c3907aad82f16726f0a233ea4ba8 Mon Sep 17 00:00:00 2001
From: onur-ozkan <work@onurozkan.dev>
Date: Sat, 23 Sep 2023 17:08:43 +0300
Subject: [PATCH] allow LTO on `proc-macro` crates with `-Zdylib-lto`

Signed-off-by: onur-ozkan <work@onurozkan.dev>
---
 compiler/rustc_codegen_llvm/messages.ftl    |  2 ++
 compiler/rustc_codegen_llvm/src/back/lto.rs | 15 ++++++++++++---
 compiler/rustc_codegen_llvm/src/errors.rs   |  4 ++++
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index ddaff36f24b1d..c0cfe39f1e0a4 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -37,6 +37,8 @@ codegen_llvm_lto_disallowed = lto can only be run for executables, cdylibs and s
 
 codegen_llvm_lto_dylib = lto cannot be used for `dylib` crate type without `-Zdylib-lto`
 
+codegen_llvm_lto_proc_macro = lto cannot be used for `proc-macro` crate type without `-Zdylib-lto`
+
 codegen_llvm_missing_features =
     add the missing features in a `target_feature` attribute
 
diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index ba263296bb454..cb5acf79135cc 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -2,7 +2,7 @@ use crate::back::write::{
     self, bitcode_section_name, save_temp_bitcode, CodegenDiagnosticsStage, DiagnosticHandlers,
 };
 use crate::errors::{
-    DynamicLinkingWithLTO, LlvmError, LtoBitcodeFromRlib, LtoDisallowed, LtoDylib,
+    DynamicLinkingWithLTO, LlvmError, LtoBitcodeFromRlib, LtoDisallowed, LtoDylib, LtoProcMacro,
 };
 use crate::llvm::{self, build_string};
 use crate::{LlvmCodegenBackend, ModuleLlvm};
@@ -36,8 +36,12 @@ pub const THIN_LTO_KEYS_INCR_COMP_FILE_NAME: &str = "thin-lto-past-keys.bin";
 
 pub fn crate_type_allows_lto(crate_type: CrateType) -> bool {
     match crate_type {
-        CrateType::Executable | CrateType::Dylib | CrateType::Staticlib | CrateType::Cdylib => true,
-        CrateType::Rlib | CrateType::ProcMacro => false,
+        CrateType::Executable
+        | CrateType::Dylib
+        | CrateType::Staticlib
+        | CrateType::Cdylib
+        | CrateType::ProcMacro => true,
+        CrateType::Rlib => false,
     }
 }
 
@@ -87,6 +91,11 @@ fn prepare_lto(
                     diag_handler.emit_err(LtoDylib);
                     return Err(FatalError);
                 }
+            } else if *crate_type == CrateType::ProcMacro {
+                if !cgcx.opts.unstable_opts.dylib_lto {
+                    diag_handler.emit_err(LtoProcMacro);
+                    return Err(FatalError);
+                }
             }
         }
 
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 264c273ba3072..665d195790c2d 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -138,6 +138,10 @@ pub(crate) struct LtoDisallowed;
 #[diag(codegen_llvm_lto_dylib)]
 pub(crate) struct LtoDylib;
 
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_lto_proc_macro)]
+pub(crate) struct LtoProcMacro;
+
 #[derive(Diagnostic)]
 #[diag(codegen_llvm_lto_bitcode_from_rlib)]
 pub(crate) struct LtoBitcodeFromRlib {