Dispose llvm::TargetMachines prior to llvm::Context being disposed

If the TargetMachine is disposed after the Context is disposed, it can
lead to use after frees in some cases.

I've observed this happening occasionally on code compiled for
aarch64-pc-windows-msvc using `-Zstack-protector=strong` but other users
have reported AVs from host aarch64-pc-windows-msvc compilers as well.

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index 8655aeec13d..db297425b03 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -25,6 +25,7 @@ use std::ffi::{CStr, CString};
 use std::fs::File;
 use std::io;
 use std::iter;
+use std::mem::ManuallyDrop;
 use std::path::Path;
 use std::slice;
 use std::sync::Arc;
@@ -734,7 +735,7 @@ pub unsafe fn optimize_thin_module(
     let llcx = llvm::LLVMRustContextCreate(cgcx.fewer_names);
     let llmod_raw = parse_module(llcx, module_name, thin_module.data(), &diag_handler)? as *const _;
     let mut module = ModuleCodegen {
-        module_llvm: ModuleLlvm { llmod_raw, llcx, tm },
+        module_llvm: ModuleLlvm { llmod_raw, llcx, tm: ManuallyDrop::new(tm) },
         name: thin_module.name().to_string(),
         kind: ModuleKind::Regular,
     };