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.

tests/codegen/emscripten-catch-unwind-wasm-eh.rs

@@ -0,0 +1,65 @@
+//@ compile-flags: -O --target wasm32-unknown-emscripten -Z emscripten-wasm-eh
+//@ needs-llvm-components: webassembly
+
+// Emscripten catch_unwind using wasm exceptions
+
+#![feature(no_core, lang_items, intrinsics, rustc_attrs)]
+#![crate_type = "lib"]
+#![no_std]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "freeze"]
+trait Freeze {}
+#[lang = "copy"]
+trait Copy {}
+
+impl<T> Copy for *mut T {}
+
+#[rustc_intrinsic]
+fn size_of<T>() -> usize {
+    loop {}
+}
+
+extern "rust-intrinsic" {
+    fn catch_unwind(
+        try_fn: fn(_: *mut u8),
+        data: *mut u8,
+        catch_fn: fn(_: *mut u8, _: *mut u8),
+    ) -> i32;
+}
+
+// CHECK-LABEL: @ptr_size
+#[no_mangle]
+pub fn ptr_size() -> usize {
+    // CHECK: ret [[PTR_SIZE:.*]]
+    size_of::<*mut u8>()
+}
+
+// CHECK-LABEL: @test_catch_unwind
+#[no_mangle]
+pub unsafe fn test_catch_unwind(
+    try_fn: fn(_: *mut u8),
+    data: *mut u8,
+    catch_fn: fn(_: *mut u8, _: *mut u8),
+) -> i32 {
+    // CHECK: start:
+    // CHECK: invoke void %try_fn(ptr %data)
+    // CHECK:         to label %__rust_try.exit unwind label %catchswitch.i
+    // CHECK:   catchswitch.i:                                    ; preds = %start
+    // CHECK:   %catchswitch1.i = catchswitch within none [label %catchpad.i] unwind to caller
+
+    // CHECK: catchpad.i:                                       ; preds = %catchswitch.i
+    // CHECK:   %catchpad2.i = catchpad within %catchswitch1.i [ptr null]
+    // CHECK:   %0 = tail call ptr @llvm.wasm.get.exception(token %catchpad2.i)
+    // CHECK:   %1 = tail call i32 @llvm.wasm.get.ehselector(token %catchpad2.i)
+    // CHECK:   call void %catch_fn(ptr %data, ptr %0) [ "funclet"(token %catchpad2.i) ]
+    // CHECK:   catchret from %catchpad2.i to label %__rust_try.exit
+
+    // CHECK: __rust_try.exit:                                  ; preds = %start, %catchpad.i
+    // CHECK:   %common.ret.op.i = phi i32 [ 0, %start ], [ 1, %catchpad.i ]
+    // CHECK:   ret i32 %common.ret.op.i
+
+    catch_unwind(try_fn, data, catch_fn)
+}