Add `UnwindAction::Terminate`

2 files changed, 77 insertions, 83 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 66bec6f30de..5bc78e5dbac 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -170,22 +170,17 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
 
         let unwind_block = match unwind {
             mir::UnwindAction::Cleanup(cleanup) => Some(self.llbb_with_cleanup(fx, cleanup)),
-            _ if fx.mir[self.bb].is_cleanup
-                && fn_abi.can_unwind
-                && !base::wants_msvc_seh(fx.cx.tcx().sess) =>
-            {
-                // Exception must not propagate out of the execution of a cleanup (doing so
-                // can cause undefined behaviour). We insert a double unwind guard for
-                // functions that can potentially unwind to protect against this.
-                //
-                // This is not necessary for SEH which does not use successive unwinding
-                // like Itanium EH. EH frames in SEH are different from normal function
-                // frames and SEH will abort automatically if an exception tries to
-                // propagate out from cleanup.
-                Some(fx.double_unwind_guard())
-            }
             mir::UnwindAction::Continue => None,
             mir::UnwindAction::Unreachable => None,
+            mir::UnwindAction::Terminate => {
+                if fx.mir[self.bb].is_cleanup && base::wants_msvc_seh(fx.cx.tcx().sess) {
+                    // SEH will abort automatically if an exception tries to
+                    // propagate out from cleanup.
+                    None
+                } else {
+                    Some(fx.terminate_block())
+                }
+            }
         };
 
         if let Some(unwind_block) = unwind_block {
@@ -253,7 +248,14 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
         instance: Instance<'_>,
         mergeable_succ: bool,
     ) -> MergingSucc {
-        if let mir::UnwindAction::Cleanup(cleanup) = unwind {
+        let unwind_target = match unwind {
+            mir::UnwindAction::Cleanup(cleanup) => Some(self.llbb_with_cleanup(fx, cleanup)),
+            mir::UnwindAction::Terminate => Some(fx.terminate_block()),
+            mir::UnwindAction::Continue => None,
+            mir::UnwindAction::Unreachable => None,
+        };
+
+        if let Some(cleanup) = unwind_target {
             let ret_llbb = if let Some(target) = destination {
                 fx.llbb(target)
             } else {
@@ -266,7 +268,7 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
                 options,
                 line_spans,
                 instance,
-                Some((ret_llbb, self.llbb_with_cleanup(fx, cleanup), self.funclet(fx))),
+                Some((ret_llbb, cleanup, self.funclet(fx))),
             );
             MergingSucc::False
         } else {
@@ -1551,62 +1553,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     fn landing_pad_for_uncached(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
         let llbb = self.llbb(bb);
         if base::wants_msvc_seh(self.cx.sess()) {
-            let funclet;
-            let ret_llbb;
-            match self.mir[bb].terminator.as_ref().map(|t| &t.kind) {
-                // This is a basic block that we're aborting the program for,
-                // notably in an `extern` function. These basic blocks are inserted
-                // so that we assert that `extern` functions do indeed not panic,
-                // and if they do we abort the process.
-                //
-                // On MSVC these are tricky though (where we're doing funclets). If
-                // we were to do a cleanuppad (like below) the normal functions like
-                // `longjmp` would trigger the abort logic, terminating the
-                // program. Instead we insert the equivalent of `catch(...)` for C++
-                // which magically doesn't trigger when `longjmp` files over this
-                // frame.
-                //
-                // Lots more discussion can be found on #48251 but this codegen is
-                // modeled after clang's for:
-                //
-                //      try {
-                //          foo();
-                //      } catch (...) {
-                //          bar();
-                //      }
-                Some(&mir::TerminatorKind::Abort) => {
-                    let cs_llbb =
-                        Bx::append_block(self.cx, self.llfn, &format!("cs_funclet{:?}", bb));
-                    let cp_llbb =
-                        Bx::append_block(self.cx, self.llfn, &format!("cp_funclet{:?}", bb));
-                    ret_llbb = cs_llbb;
-
-                    let mut cs_bx = Bx::build(self.cx, cs_llbb);
-                    let cs = cs_bx.catch_switch(None, None, &[cp_llbb]);
-
-                    // The "null" here is actually a RTTI type descriptor for the
-                    // C++ personality function, but `catch (...)` has no type so
-                    // it's null. The 64 here is actually a bitfield which
-                    // represents that this is a catch-all block.
-                    let mut cp_bx = Bx::build(self.cx, cp_llbb);
-                    let null = cp_bx.const_null(
-                        cp_bx.type_i8p_ext(cp_bx.cx().data_layout().instruction_address_space),
-                    );
-                    let sixty_four = cp_bx.const_i32(64);
-                    funclet = cp_bx.catch_pad(cs, &[null, sixty_four, null]);
-                    cp_bx.br(llbb);
-                }
-                _ => {
-                    let cleanup_llbb =
-                        Bx::append_block(self.cx, self.llfn, &format!("funclet_{:?}", bb));
-                    ret_llbb = cleanup_llbb;
-                    let mut cleanup_bx = Bx::build(self.cx, cleanup_llbb);
-                    funclet = cleanup_bx.cleanup_pad(None, &[]);
-                    cleanup_bx.br(llbb);
-                }
-            }
+            let cleanup_bb = Bx::append_block(self.cx, self.llfn, &format!("funclet_{:?}", bb));
+            let mut cleanup_bx = Bx::build(self.cx, cleanup_bb);
+            let funclet = cleanup_bx.cleanup_pad(None, &[]);
+            cleanup_bx.br(llbb);
             self.funclets[bb] = Some(funclet);
-            ret_llbb
+            cleanup_bb
         } else {
             let cleanup_llbb = Bx::append_block(self.cx, self.llfn, "cleanup");
             let mut cleanup_bx = Bx::build(self.cx, cleanup_llbb);
@@ -1633,26 +1585,68 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         })
     }
 
-    fn double_unwind_guard(&mut self) -> Bx::BasicBlock {
-        self.double_unwind_guard.unwrap_or_else(|| {
-            assert!(!base::wants_msvc_seh(self.cx.sess()));
+    fn terminate_block(&mut self) -> Bx::BasicBlock {
+        self.terminate_block.unwrap_or_else(|| {
+            let funclet;
+            let llbb;
+            let mut bx;
+            if base::wants_msvc_seh(self.cx.sess()) {
+                // This is a basic block that we're aborting the program for,
+                // notably in an `extern` function. These basic blocks are inserted
+                // so that we assert that `extern` functions do indeed not panic,
+                // and if they do we abort the process.
+                //
+                // On MSVC these are tricky though (where we're doing funclets). If
+                // we were to do a cleanuppad (like below) the normal functions like
+                // `longjmp` would trigger the abort logic, terminating the
+                // program. Instead we insert the equivalent of `catch(...)` for C++
+                // which magically doesn't trigger when `longjmp` files over this
+                // frame.
+                //
+                // Lots more discussion can be found on #48251 but this codegen is
+                // modeled after clang's for:
+                //
+                //      try {
+                //          foo();
+                //      } catch (...) {
+                //          bar();
+                //      }
+                llbb = Bx::append_block(self.cx, self.llfn, "cs_terminate");
+                let cp_llbb = Bx::append_block(self.cx, self.llfn, "cp_terminate");
+
+                let mut cs_bx = Bx::build(self.cx, llbb);
+                let cs = cs_bx.catch_switch(None, None, &[llbb]);
+
+                // The "null" here is actually a RTTI type descriptor for the
+                // C++ personality function, but `catch (...)` has no type so
+                // it's null. The 64 here is actually a bitfield which
+                // represents that this is a catch-all block.
+                bx = Bx::build(self.cx, cp_llbb);
+                let null =
+                    bx.const_null(bx.type_i8p_ext(bx.cx().data_layout().instruction_address_space));
+                let sixty_four = bx.const_i32(64);
+                funclet = Some(bx.catch_pad(cs, &[null, sixty_four, null]));
+            } else {
+                llbb = Bx::append_block(self.cx, self.llfn, "terminate");
+                bx = Bx::build(self.cx, llbb);
+
+                let llpersonality = self.cx.eh_personality();
+                bx.cleanup_landing_pad(llpersonality);
 
-            let llbb = Bx::append_block(self.cx, self.llfn, "abort");
-            let mut bx = Bx::build(self.cx, llbb);
-            self.set_debug_loc(&mut bx, mir::SourceInfo::outermost(self.mir.span));
+                funclet = None;
+            }
 
-            let llpersonality = self.cx.eh_personality();
-            bx.cleanup_landing_pad(llpersonality);
+            self.set_debug_loc(&mut bx, mir::SourceInfo::outermost(self.mir.span));
 
             let (fn_abi, fn_ptr) = common::build_langcall(&bx, None, LangItem::PanicCannotUnwind);
             let fn_ty = bx.fn_decl_backend_type(&fn_abi);
 
-            let llret = bx.call(fn_ty, Some(&fn_abi), fn_ptr, &[], None);
+            let llret = bx.call(fn_ty, Some(&fn_abi), fn_ptr, &[], funclet.as_ref());
             bx.do_not_inline(llret);
 
             bx.unreachable();
 
-            self.double_unwind_guard = Some(llbb);
+            self.terminate_block = Some(llbb);
             llbb
         })
     }
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 189549953d9..0b4456dba30 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -74,7 +74,7 @@ pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     unreachable_block: Option<Bx::BasicBlock>,
 
     /// Cached double unwind guarding block
-    double_unwind_guard: Option<Bx::BasicBlock>,
+    terminate_block: Option<Bx::BasicBlock>,
 
     /// The location where each MIR arg/var/tmp/ret is stored. This is
     /// usually an `PlaceRef` representing an alloca, but not always:
@@ -189,7 +189,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         personality_slot: None,
         cached_llbbs,
         unreachable_block: None,
-        double_unwind_guard: None,
+        terminate_block: None,
         cleanup_kinds,
         landing_pads: IndexVec::from_elem(None, &mir.basic_blocks),
         funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks.len()),