Remove the ThinLTO CU hack

This reverts #46722, commit e0ab5d5feb4eb2d8af11b8dd9446c2b45fada8af.

Since #111167, commit 10b69dde3fd15334ea2382d2dc9e9a261de1afaf, we are
generating DWARF subprograms in a way that is meant to be more compatible
with LLVM's expectations, so hopefully we don't need this workaround
rewriting CUs anymore.

2 files changed, 0 insertions, 55 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index d2e01708a37..604f68eb6a4 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -25,7 +25,6 @@ use std::fs::File;
 use std::io;
 use std::iter;
 use std::path::Path;
-use std::ptr;
 use std::slice;
 use std::sync::Arc;
 
@@ -709,17 +708,6 @@ pub unsafe fn optimize_thin_module(
         let llmod = module.module_llvm.llmod();
         save_temp_bitcode(cgcx, &module, "thin-lto-input");
 
-        // Before we do much else find the "main" `DICompileUnit` that we'll be
-        // using below. If we find more than one though then rustc has changed
-        // in a way we're not ready for, so generate an ICE by returning
-        // an error.
-        let mut cu1 = ptr::null_mut();
-        let mut cu2 = ptr::null_mut();
-        llvm::LLVMRustThinLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2);
-        if !cu2.is_null() {
-            return Err(write::llvm_err(&diag_handler, LlvmError::MultipleSourceDiCompileUnit));
-        }
-
         // Up next comes the per-module local analyses that we do for Thin LTO.
         // Each of these functions is basically copied from the LLVM
         // implementation and then tailored to suit this implementation. Ideally
@@ -766,43 +754,6 @@ pub unsafe fn optimize_thin_module(
             save_temp_bitcode(cgcx, &module, "thin-lto-after-import");
         }
 
-        // Ok now this is a bit unfortunate. This is also something you won't
-        // find upstream in LLVM's ThinLTO passes! This is a hack for now to
-        // work around bugs in LLVM.
-        //
-        // First discovered in #45511 it was found that as part of ThinLTO
-        // importing passes LLVM will import `DICompileUnit` metadata
-        // information across modules. This means that we'll be working with one
-        // LLVM module that has multiple `DICompileUnit` instances in it (a
-        // bunch of `llvm.dbg.cu` members). Unfortunately there's a number of
-        // bugs in LLVM's backend which generates invalid DWARF in a situation
-        // like this:
-        //
-        //  https://bugs.llvm.org/show_bug.cgi?id=35212
-        //  https://bugs.llvm.org/show_bug.cgi?id=35562
-        //
-        // While the first bug there is fixed the second ended up causing #46346
-        // which was basically a resurgence of #45511 after LLVM's bug 35212 was
-        // fixed.
-        //
-        // This function below is a huge hack around this problem. The function
-        // below is defined in `PassWrapper.cpp` and will basically "merge"
-        // all `DICompileUnit` instances in a module. Basically it'll take all
-        // the objects, rewrite all pointers of `DISubprogram` to point to the
-        // first `DICompileUnit`, and then delete all the other units.
-        //
-        // This is probably mangling to the debug info slightly (but hopefully
-        // not too much) but for now at least gets LLVM to emit valid DWARF (or
-        // so it appears). Hopefully we can remove this once upstream bugs are
-        // fixed in LLVM.
-        {
-            let _timer = cgcx
-                .prof
-                .generic_activity_with_arg("LLVM_thin_lto_patch_debuginfo", thin_module.name());
-            llvm::LLVMRustThinLTOPatchDICompileUnit(llmod, cu1);
-            save_temp_bitcode(cgcx, &module, "thin-lto-after-patch");
-        }
-
         // Alright now that we've done everything related to the ThinLTO
         // analysis it's time to run some optimizations! Here we use the same
         // `run_pass_manager` as the "fat" LTO above except that we tell it to
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 61365e6dc4b..d5be678c1bb 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -2480,12 +2480,6 @@ extern "C" {
         len: usize,
         out_len: &mut usize,
     ) -> *const u8;
-    pub fn LLVMRustThinLTOGetDICompileUnit(
-        M: &Module,
-        CU1: &mut *mut c_void,
-        CU2: &mut *mut c_void,
-    );
-    pub fn LLVMRustThinLTOPatchDICompileUnit(M: &Module, CU: *mut c_void);
 
     pub fn LLVMRustLinkerNew(M: &Module) -> &mut Linker<'_>;
     pub fn LLVMRustLinkerAdd(