Add support for wasm exception handling to Emscripten target

Author: hoodmane

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -109,9 +109,9 @@ unsafe fn configure_llvm(sess: &Session) {
             add("-wasm-enable-eh", false);
         }
 
-        if sess.target.os == "emscripten" && sess.panic_strategy() == PanicStrategy::Unwind {
-            add("-enable-emscripten-cxx-exceptions", false);
-        }
+        // if sess.target.os == "emscripten" && sess.panic_strategy() == PanicStrategy::Unwind {
+        //     add("-enable-emscripten-cxx-exceptions", false);
+        // }
 
         // HACK(eddyb) LLVM inserts `llvm.assume` calls to preserve align attributes
         // during inlining. Unfortunately these may block other optimizations.

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2466,10 +2466,10 @@ fn add_order_independent_options(
     }
 
     if sess.target.os == "emscripten" {
-        cmd.cc_arg("-s").cc_arg(if sess.panic_strategy() == PanicStrategy::Abort {
-            "DISABLE_EXCEPTION_CATCHING=1"
+        cmd.cc_arg(if sess.panic_strategy() == PanicStrategy::Abort {
+            "-sDISABLE_EXCEPTION_CATCHING=1"
         } else {
-            "DISABLE_EXCEPTION_CATCHING=0"
+            "-fwasm-exceptions"
         });
     }
 

compiler/rustc_codegen_ssa/src/base.rs

@@ -388,7 +388,7 @@ pub(crate) fn build_shift_expr_rhs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 // exceptions. This means that the VM does the unwinding for
 // us
 pub fn wants_wasm_eh(sess: &Session) -> bool {
-    sess.target.is_like_wasm && sess.target.os != "emscripten"
+    sess.target.is_like_wasm
 }
 
 /// Returns `true` if this session's target will use SEH-based unwinding.

compiler/rustc_passes/src/weak_lang_items.rs

@@ -26,9 +26,9 @@ pub(crate) fn check_crate(
     if items.eh_personality().is_none() {
         items.missing.push(LangItem::EhPersonality);
     }
-    if tcx.sess.target.os == "emscripten" && items.eh_catch_typeinfo().is_none() {
-        items.missing.push(LangItem::EhCatchTypeinfo);
-    }
+    // if tcx.sess.target.os == "emscripten" && items.eh_catch_typeinfo().is_none() {
+    //     items.missing.push(LangItem::EhCatchTypeinfo);
+    // }
 
     visit::Visitor::visit_crate(&mut WeakLangItemVisitor { tcx, items }, krate);
 

library/panic_unwind/src/lib.rs

@@ -31,10 +31,7 @@ use core::any::Any;
 use core::panic::PanicPayload;
 
 cfg_if::cfg_if! {
-    if #[cfg(target_os = "emscripten")] {
-        #[path = "emcc.rs"]
-        mod imp;
-    } else if #[cfg(target_os = "hermit")] {
+    if #[cfg(target_os = "hermit")] {
         #[path = "hermit.rs"]
         mod imp;
     } else if #[cfg(target_os = "l4re")] {

library/unwind/src/lib.rs

@@ -3,10 +3,7 @@
 #![feature(link_cfg)]
 #![feature(staged_api)]
 #![cfg_attr(not(target_env = "msvc"), feature(libc))]
-#![cfg_attr(
-    all(target_family = "wasm", not(target_os = "emscripten")),
-    feature(simd_wasm64, wasm_exception_handling_intrinsics)
-)]
+#![cfg_attr(all(target_family = "wasm"), feature(simd_wasm64, wasm_exception_handling_intrinsics))]
 #![allow(internal_features)]
 
 // Force libc to be included even if unused. This is required by many platforms.