Function optimize

crates/rustc_codegen_nvvm/src/back.rs:316–398

TODO: We use rustc's optimization approach from when it used llvm 7, because many things are incompatible with llvm 7 nowadays. Although we should probably consult a rustc dev on whether any big things were discovered in that timespan that we should modify.

(
    cgcx: &CodegenContext<NvvmCodegenBackend>,
    diag_handler: &Handler,
    module: &ModuleCodegen<LlvmMod>,
    config: &ModuleConfig,
)

// are incompatible with llvm 7 nowadays. Although we should probably consult a rustc dev on whether
// any big things were discovered in that timespan that we should modify.
pub(crate) unsafe fn optimize(
    cgcx: &CodegenContext<NvvmCodegenBackend>,
    diag_handler: &Handler,
    module: &ModuleCodegen<LlvmMod>,
    config: &ModuleConfig,
) -> Result<(), FatalError> {
    let _timer = cgcx
        .prof
        .generic_activity_with_arg("LLVM_module_optimize", &module.name[..]);

    let llmod = &*module.module_llvm.llmod;

    let module_name = module.name.clone();
    let module_name = Some(&module_name[..]);

    if config.emit_no_opt_bc {
        let out = cgcx
            .output_filenames
            .temp_path_ext("no-opt.bc", module_name);
        let out = path_to_c_string(&out);
        llvm::LLVMWriteBitcodeToFile(llmod, out.as_ptr());
    }

    let tm_factory_config = TargetMachineFactoryConfig {
        split_dwarf_file: None,
    };

    let tm = (cgcx.tm_factory)(tm_factory_config).expect("failed to create target machine");

    if config.opt_level.is_some() {
        let fpm = llvm::LLVMCreateFunctionPassManagerForModule(llmod);
        let mpm = llvm::LLVMCreatePassManager();

        let addpass = |pass_name: &str| {
            let pass_name = CString::new(pass_name).unwrap();
            let pass = llvm::LLVMRustFindAndCreatePass(pass_name.as_ptr());
            if pass.is_none() {
                return false;
            }
            let pass = pass.unwrap();
            let pass_manager = match llvm::LLVMRustPassKind(pass) {
                llvm::PassKind::Function => &fpm,
                llvm::PassKind::Module => &mpm,
                llvm::PassKind::Other => {
                    diag_handler.err("Encountered LLVM pass kind we can't handle");
                    return true;
                }
            };
            llvm::LLVMRustAddPass(pass_manager, pass);
            true
        };

        if !config.no_prepopulate_passes {
            llvm::LLVMRustAddAnalysisPasses(tm, fpm, llmod);
            llvm::LLVMRustAddAnalysisPasses(tm, mpm, llmod);
            let opt_level = config
                .opt_level
                .map_or(llvm::CodeGenOptLevel::None, |x| to_llvm_opt_settings(x).0);