Rollup merge of #131830 - hoodmane:emscripten-wasm-eh, r=workingjubilee

Add support for wasm exception handling to Emscripten target

This is a draft because we need some additional setting for the Emscripten target to select between the old exception handling and the new exception handling. I don't know how to add a setting like that, would appreciate advice from Rust folks. We could maybe choose to use the new exception handling if `Ctarget-feature=+exception-handling` is passed? I tried this but I get errors from llvm so I'm not doing it right.

2 files changed, 7 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 2587d6dfdc4..e4b3ad19801 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -2451,10 +2451,12 @@ 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 if sess.opts.unstable_opts.emscripten_wasm_eh {
+            "-fwasm-exceptions"
         } else {
-            "DISABLE_EXCEPTION_CATCHING=0"
+            "-sDISABLE_EXCEPTION_CATCHING=0"
         });
     }
 
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 77e1fed720d..544578b29f1 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -388,7 +388,8 @@ 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
+        && (sess.target.os != "emscripten" || sess.opts.unstable_opts.emscripten_wasm_eh)
 }
 
 /// Returns `true` if this session's target will use SEH-based unwinding.