Remove LLVMRustMarkAllFunctionsNounwind

This was originally introduced in #10916 as a way to remove all landing
pads when performing LTO. However this is no longer necessary today
since rustc properly marks all functions and call-sites as nounwind
where appropriate.

In fact this is incorrect in the presence of `extern "C-unwind"` which
must create a landing pad when compiled with `-C panic=abort` so that
foreign exceptions are caught and properly turned into aborts.

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -349,13 +349,6 @@ fn fat_lto(
             );
             save_temp_bitcode(cgcx, &module, "lto.after-restriction");
         }
-
-        if cgcx.no_landing_pads {
-            unsafe {
-                llvm::LLVMRustMarkAllFunctionsNounwind(llmod);
-            }
-            save_temp_bitcode(cgcx, &module, "lto.after-nounwind");
-        }
     }
 
     Ok(LtoModuleCodegen::Fat { module: Some(module), _serialized_bitcode: serialized_bitcode })
@@ -770,16 +763,6 @@ pub unsafe fn optimize_thin_module(
             return Err(write::llvm_err(&diag_handler, msg));
         }
 
-        // Like with "fat" LTO, get some better optimizations if landing pads
-        // are disabled by removing all landing pads.
-        if cgcx.no_landing_pads {
-            let _timer = cgcx
-                .prof
-                .generic_activity_with_arg("LLVM_thin_lto_remove_landing_pads", thin_module.name());
-            llvm::LLVMRustMarkAllFunctionsNounwind(llmod);
-            save_temp_bitcode(cgcx, &module, "thin-lto-after-nounwind");
-        }
-
         // 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

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2329,7 +2329,6 @@ extern "C" {
     pub fn LLVMRustSetNormalizedTarget(M: &Module, triple: *const c_char);
     pub fn LLVMRustAddAlwaysInlinePass(P: &PassManagerBuilder, AddLifetimes: bool);
     pub fn LLVMRustRunRestrictionPass(M: &Module, syms: *const *const c_char, len: size_t);
-    pub fn LLVMRustMarkAllFunctionsNounwind(M: &Module);
 
     pub fn LLVMRustOpenArchive(path: *const c_char) -> Option<&'static mut Archive>;
     pub fn LLVMRustArchiveIteratorNew(AR: &Archive) -> &mut ArchiveIterator<'_>;

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -32,7 +32,7 @@ use rustc_session::Session;
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::sym;
 use rustc_span::{BytePos, FileName, InnerSpan, Pos, Span};
-use rustc_target::spec::{MergeFunctions, PanicStrategy, SanitizerSet};
+use rustc_target::spec::{MergeFunctions, SanitizerSet};
 
 use std::any::Any;
 use std::fs;
@@ -313,7 +313,6 @@ pub struct CodegenContext<B: WriteBackendMethods> {
     pub backend: B,
     pub prof: SelfProfilerRef,
     pub lto: Lto,
-    pub no_landing_pads: bool,
     pub save_temps: bool,
     pub fewer_names: bool,
     pub time_trace: bool,
@@ -1039,7 +1038,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
         crate_types: sess.crate_types().to_vec(),
         each_linked_rlib_for_lto,
         lto: sess.lto(),
-        no_landing_pads: sess.panic_strategy() == PanicStrategy::Abort,
         fewer_names: sess.fewer_names(),
         save_temps: sess.opts.cg.save_temps,
         time_trace: sess.opts.debugging_opts.llvm_time_trace,

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -1168,25 +1168,6 @@ extern "C" void LLVMRustRunRestrictionPass(LLVMModuleRef M, char **Symbols,
   passes.run(*unwrap(M));
 }
 
-extern "C" void LLVMRustMarkAllFunctionsNounwind(LLVMModuleRef M) {
-  for (Module::iterator GV = unwrap(M)->begin(), E = unwrap(M)->end(); GV != E;
-       ++GV) {
-    GV->setDoesNotThrow();
-    Function *F = dyn_cast<Function>(GV);
-    if (F == nullptr)
-      continue;
-
-    for (Function::iterator B = F->begin(), BE = F->end(); B != BE; ++B) {
-      for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ++I) {
-        if (isa<InvokeInst>(I)) {
-          InvokeInst *CI = cast<InvokeInst>(I);
-          CI->setDoesNotThrow();
-        }
-      }
-    }
-  }
-}
-
 extern "C" void
 LLVMRustSetDataLayoutFromTargetMachine(LLVMModuleRef Module,
                                        LLVMTargetMachineRef TMR) {