diff options
Diffstat (limited to 'src/librustc_codegen_llvm/back/write.rs')
| -rw-r--r-- | src/librustc_codegen_llvm/back/write.rs | 36 |
1 files changed, 34 insertions, 2 deletions
diff --git a/src/librustc_codegen_llvm/back/write.rs b/src/librustc_codegen_llvm/back/write.rs index 95281e2445a..ba1315956fb 100644 --- a/src/librustc_codegen_llvm/back/write.rs +++ b/src/librustc_codegen_llvm/back/write.rs @@ -633,7 +633,7 @@ unsafe fn optimize(cgcx: &CodegenContext, None, &format!("llvm module passes [{}]", module_name.unwrap()), || { - llvm::LLVMRunPassManager(mpm, llmod) + llvm::LLVMRunPassManager(mpm, llmod); }); // Deallocate managers that we're now done with @@ -691,6 +691,38 @@ unsafe fn codegen(cgcx: &CodegenContext, create_msvc_imps(cgcx, llcx, llmod); } + // Ok now this one's a super interesting invocations. SIMD in rustc is + // difficult where we want some parts of the program to be able to use + // some SIMD features while other parts of the program don't. The real + // tough part is that we want this to actually work correctly! + // + // We go to great lengths to make sure this works, and one crucial + // aspect is that vector arguments (simd types) are never passed by + // value in the ABI of functions. It turns out, however, that LLVM will + // undo our "clever work" of passing vector types by reference. Its + // argument promotion pass will promote these by-ref arguments to + // by-val. That, however, introduces codegen errors! + // + // The upstream LLVM bug [1] has unfortunatey not really seen a lot of + // activity. The Rust bug [2], however, has seen quite a lot of reports + // of this in the wild. As a result, this is worked around locally here. + // We have a custom transformation, `LLVMRustDemoteSimdArguments`, which + // does the opposite of argument promotion by demoting any by-value SIMD + // arguments in function signatures to pointers intead of being + // by-value. + // + // This operates at the LLVM IR layer because LLVM is thwarting our + // codegen and this is the only chance we get to make sure it's correct + // before we hit codegen. + // + // Hopefully one day the upstream LLVM bug will be fixed and we'll no + // longer need this! + // + // [1]: https://bugs.llvm.org/show_bug.cgi?id=37358 + // [2]: https://github.com/rust-lang/rust/issues/50154 + llvm::LLVMRustDemoteSimdArguments(llmod); + cgcx.save_temp_bitcode(&module, "simd-demoted"); + // A codegen-specific pass manager is used to generate object // files for an LLVM module. // @@ -1540,7 +1572,7 @@ fn start_executing_work(tcx: TyCtxt, // Compute the set of symbols we need to retain when doing LTO (if we need to) let exported_symbols = { - let mut exported_symbols = FxHashMap(); + let mut exported_symbols = FxHashMap::default(); let copy_symbols = |cnum| { let symbols = tcx.exported_symbols(cnum) |