Add support for storing code model to LLVM module IR

src/librustc_codegen_llvm/back/write.rs

@@ -108,7 +108,7 @@ fn to_llvm_relocation_model(relocation_model: RelocModel) -> llvm::RelocModel {
     }
 }
 
-fn to_llvm_code_model(code_model: Option<CodeModel>) -> llvm::CodeModel {
+pub(crate) fn to_llvm_code_model(code_model: Option<CodeModel>) -> llvm::CodeModel {
     match code_model {
         Some(CodeModel::Tiny) => llvm::CodeModel::Tiny,
         Some(CodeModel::Small) => llvm::CodeModel::Small,

src/librustc_codegen_llvm/context.rs

@@ -1,4 +1,5 @@
 use crate::attributes;
+use crate::back::write::to_llvm_code_model;
 use crate::callee::get_fn;
 use crate::coverageinfo;
 use crate::debuginfo;
@@ -181,6 +182,13 @@ pub unsafe fn create_module(
         }
     }
 
+    // Linking object files with different code models is undefined behavior
+    // because the compiler would have to generate additional code (to span
+    // longer jumps) if a larger code model is used with a smaller one.
+    //
+    // See https://reviews.llvm.org/D52322 and https://reviews.llvm.org/D52323.
+    llvm::LLVMRustSetModuleCodeModel(llmod, to_llvm_code_model(sess.code_model()));
+
     // If skipping the PLT is enabled, we need to add some module metadata
     // to ensure intrinsic calls don't use it.
     if !sess.needs_plt() {

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -2129,6 +2129,7 @@ extern "C" {
     pub fn LLVMRustUnsetComdat(V: &Value);
     pub fn LLVMRustSetModulePICLevel(M: &Module);
     pub fn LLVMRustSetModulePIELevel(M: &Module);
+    pub fn LLVMRustSetModuleCodeModel(M: &Module, Model: CodeModel);
     pub fn LLVMRustModuleBufferCreate(M: &Module) -> &'static mut ModuleBuffer;
     pub fn LLVMRustModuleBufferPtr(p: &ModuleBuffer) -> *const u8;
     pub fn LLVMRustModuleBufferLen(p: &ModuleBuffer) -> usize;

src/rustllvm/PassWrapper.cpp

@@ -1163,6 +1163,14 @@ extern "C" void LLVMRustSetModulePIELevel(LLVMModuleRef M) {
   unwrap(M)->setPIELevel(PIELevel::Level::Large);
 }
 
+extern "C" void LLVMRustSetModuleCodeModel(LLVMModuleRef M,
+                                           LLVMRustCodeModel Model) {
+  auto CM = fromRust(Model);
+  if (!CM.hasValue())
+    return;
+  unwrap(M)->setCodeModel(*CM);
+}
+
 // Here you'll find an implementation of ThinLTO as used by the Rust compiler
 // right now. This ThinLTO support is only enabled on "recent ish" versions of
 // LLVM, and otherwise it's just blanket rejected from other compilers.

src/test/codegen/codemodels.rs

@@ -0,0 +1,18 @@
+// revisions: NOMODEL MODEL-SMALL MODEL-KERNEL MODEL-MEDIUM MODEL-LARGE
+//[NOMODEL] compile-flags:
+//[MODEL-SMALL] compile-flags: -C code-model=small
+//[MODEL-KERNEL] compile-flags: -C code-model=kernel
+//[MODEL-MEDIUM] compile-flags: -C code-model=medium
+//[MODEL-LARGE] compile-flags: -C code-model=large
+
+#![crate_type = "lib"]
+
+// MODEL-SMALL: !llvm.module.flags = !{{{.*}}}
+// MODEL-SMALL: !{{[0-9]+}} = !{i32 1, !"Code Model", i32 1}
+// MODEL-KERNEL: !llvm.module.flags = !{{{.*}}}
+// MODEL-KERNEL: !{{[0-9]+}} = !{i32 1, !"Code Model", i32 2}
+// MODEL-MEDIUM: !llvm.module.flags = !{{{.*}}}
+// MODEL-MEDIUM: !{{[0-9]+}} = !{i32 1, !"Code Model", i32 3}
+// MODEL-LARGE: !llvm.module.flags = !{{{.*}}}
+// MODEL-LARGE: !{{[0-9]+}} = !{i32 1, !"Code Model", i32 4}
+// NOMODEL-NOT: Code Model