From 98190b716829fd4edbf1b364a1a662de9a9ca7bb Mon Sep 17 00:00:00 2001 From: "Cliff L. Biffle" Date: Mon, 4 Apr 2022 11:03:03 -0700 Subject: [PATCH] Revert "Work around invalid DWARF bugs for fat LTO" Since September, the toolchain has not been generating reliable DWARF information for static variables when LTO is on. This has affected projects in the embedded space where the use of LTO is typical. In our case, it has kept us from bumping past the 2021-09-22 nightly toolchain lest our debugger break. This has been a pretty dramatic regression for people using debuggers and static variables. See #90357 for more info and a repro case. This commit is a mechanical revert of d5de680e20def848751cb3c11e1182408112b1d3 from PR #89041, which caused the issue. (Note on that PR that the commit's author has requested it be reverted.) I have locally verified that this fixes #90357 by restoring the functionality of both the repro case I posted on that bug, and debugger behavior on real programs. There do not appear to be test cases for this in the toolchain; if I've missed them, point me at 'em and I'll update them. --- compiler/rustc_codegen_llvm/src/back/lto.rs | 18 ++---------------- compiler/rustc_codegen_llvm/src/llvm/ffi.rs | 8 ++++++-- .../rustc_llvm/llvm-wrapper/PassWrapper.cpp | 4 ++-- 3 files changed, 10 insertions(+), 20 deletions(-) diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs index 0f5b1c08ec2dc..266ed6d8b6f30 100644 --- a/compiler/rustc_codegen_llvm/src/back/lto.rs +++ b/compiler/rustc_codegen_llvm/src/back/lto.rs @@ -325,20 +325,6 @@ 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(); @@ -757,7 +743,7 @@ pub unsafe fn optimize_thin_module( // an error. let mut cu1 = ptr::null_mut(); let mut cu2 = ptr::null_mut(); - llvm::LLVMRustLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2); + llvm::LLVMRustThinLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2); if !cu2.is_null() { let msg = "multiple source DICompileUnits found"; return Err(write::llvm_err(&diag_handler, msg)); @@ -846,7 +832,7 @@ pub unsafe fn optimize_thin_module( let _timer = cgcx .prof .generic_activity_with_arg("LLVM_thin_lto_patch_debuginfo", thin_module.name()); - llvm::LLVMRustLTOPatchDICompileUnit(llmod, cu1); + llvm::LLVMRustThinLTOPatchDICompileUnit(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 375b9927c8672..db018aeac1385 100644 --- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs +++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs @@ -2506,8 +2506,12 @@ extern "C" { len: usize, out_len: &mut usize, ) -> *const u8; - 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 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( diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp index 7030fd53704dd..e3ee21c80859e 100644 --- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp +++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp @@ -1611,7 +1611,7 @@ 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 -LLVMRustLTOGetDICompileUnit(LLVMModuleRef Mod, +LLVMRustThinLTOGetDICompileUnit(LLVMModuleRef Mod, DICompileUnit **A, DICompileUnit **B) { Module *M = unwrap(Mod); @@ -1629,7 +1629,7 @@ LLVMRustLTOGetDICompileUnit(LLVMModuleRef Mod, // Rewrite all `DICompileUnit` pointers to the `DICompileUnit` specified. See // the comment in `back/lto.rs` for why this exists. extern "C" void -LLVMRustLTOPatchDICompileUnit(LLVMModuleRef Mod, DICompileUnit *Unit) { +LLVMRustThinLTOPatchDICompileUnit(LLVMModuleRef Mod, DICompileUnit *Unit) { Module *M = unwrap(Mod); // If the original source module didn't have a `DICompileUnit` then try to