Rollup merge of #89041 - sticnarf:sticnarf/fat-lto-dwarf, r=nagisa

Work around invalid DWARF bugs for fat LTO

This PR applies the same workaround in #46772 to fat LTO.

It seems to fix the bug reported in https://github.com/rust-lang/rust/issues/66118#issuecomment-917434036.

3 files changed, 20 insertions, 10 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index f612785e5a4..99b30264d09 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -325,6 +325,20 @@ fn fat_lto(
         drop(linker);
         save_temp_bitcode(&cgcx, &module, "lto.input");
 
+        // Fat LTO also suffers from the invalid DWARF issue similar to Thin LTO.
+        // Here we rewrite all `DICompileUnit` pointers if there is only one `DICompileUnit`.
+        // This only works around the problem when codegen-units = 1.
+        // Refer to the comments in the `optimize_thin_module` function for more details.
+        let mut cu1 = ptr::null_mut();
+        let mut cu2 = ptr::null_mut();
+        unsafe { llvm::LLVMRustLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2) };
+        if !cu2.is_null() {
+            let _timer =
+                cgcx.prof.generic_activity_with_arg("LLVM_fat_lto_patch_debuginfo", &*module.name);
+            unsafe { llvm::LLVMRustLTOPatchDICompileUnit(llmod, cu1) };
+            save_temp_bitcode(cgcx, &module, "fat-lto-after-patch");
+        }
+
         // Internalize everything below threshold to help strip out more modules and such.
         unsafe {
             let ptr = symbols_below_threshold.as_ptr();
@@ -748,7 +762,7 @@ pub unsafe fn optimize_thin_module(
         // an error.
         let mut cu1 = ptr::null_mut();
         let mut cu2 = ptr::null_mut();
-        llvm::LLVMRustThinLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2);
+        llvm::LLVMRustLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2);
         if !cu2.is_null() {
             let msg = "multiple source DICompileUnits found";
             return Err(write::llvm_err(&diag_handler, msg));
@@ -847,7 +861,7 @@ pub unsafe fn optimize_thin_module(
             let _timer = cgcx
                 .prof
                 .generic_activity_with_arg("LLVM_thin_lto_patch_debuginfo", thin_module.name());
-            llvm::LLVMRustThinLTOPatchDICompileUnit(llmod, cu1);
+            llvm::LLVMRustLTOPatchDICompileUnit(llmod, cu1);
             save_temp_bitcode(cgcx, &module, "thin-lto-after-patch");
         }
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 3f2ed02d90d..d8c2a345fb0 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -2377,12 +2377,8 @@ 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 LLVMRustLTOGetDICompileUnit(M: &Module, CU1: &mut *mut c_void, CU2: &mut *mut c_void);
+    pub fn LLVMRustLTOPatchDICompileUnit(M: &Module, CU: *mut c_void);
 
     pub fn LLVMRustLinkerNew(M: &'a Module) -> &'a mut Linker<'a>;
     pub fn LLVMRustLinkerAdd(
diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
index 8dbacd71fc1..1a0cfd58885 100644
--- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
@@ -1747,7 +1747,7 @@ LLVMRustGetBitcodeSliceFromObjectData(const char *data,
 // Rewrite all `DICompileUnit` pointers to the `DICompileUnit` specified. See
 // the comment in `back/lto.rs` for why this exists.
 extern "C" void
-LLVMRustThinLTOGetDICompileUnit(LLVMModuleRef Mod,
+LLVMRustLTOGetDICompileUnit(LLVMModuleRef Mod,
                                 DICompileUnit **A,
                                 DICompileUnit **B) {
   Module *M = unwrap(Mod);
@@ -1765,7 +1765,7 @@ LLVMRustThinLTOGetDICompileUnit(LLVMModuleRef Mod,
 // Rewrite all `DICompileUnit` pointers to the `DICompileUnit` specified. See
 // the comment in `back/lto.rs` for why this exists.
 extern "C" void
-LLVMRustThinLTOPatchDICompileUnit(LLVMModuleRef Mod, DICompileUnit *Unit) {
+LLVMRustLTOPatchDICompileUnit(LLVMModuleRef Mod, DICompileUnit *Unit) {
   Module *M = unwrap(Mod);
 
   // If the original source module didn't have a `DICompileUnit` then try to