From d5652f522c696f27c07ddbeff9d25c43c6de34fc Mon Sep 17 00:00:00 2001
From: Nick Fitzgerald <fitzgen@gmail.com>
Date: Thu, 10 Oct 2024 08:19:51 -0700
Subject: [PATCH] Implement the `ref.cast` Wasm GC instruction (#9437)

---
 crates/cranelift/src/lib.rs                   |  2 ++
 .../src/translate/code_translator.rs          | 33 ++++++++++++++++---
 crates/environ/src/trap_encoding.rs           |  5 +++
 tests/wast.rs                                 |  2 --
 4 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/crates/cranelift/src/lib.rs b/crates/cranelift/src/lib.rs
index bf03d02d8eb8..73772ac5cb12 100644
--- a/crates/cranelift/src/lib.rs
+++ b/crates/cranelift/src/lib.rs
@@ -55,6 +55,8 @@ pub const TRAP_HEAP_MISALIGNED: TrapCode =
     TrapCode::unwrap_user(Trap::HeapMisaligned as u8 + TRAP_OFFSET);
 pub const TRAP_TABLE_OUT_OF_BOUNDS: TrapCode =
     TrapCode::unwrap_user(Trap::TableOutOfBounds as u8 + TRAP_OFFSET);
+pub const TRAP_CAST_FAILURE: TrapCode =
+    TrapCode::unwrap_user(Trap::CastFailure as u8 + TRAP_OFFSET);
 
 /// Creates a new cranelift `Signature` with no wasm params/results for the
 /// given calling convention.
diff --git a/crates/cranelift/src/translate/code_translator.rs b/crates/cranelift/src/translate/code_translator.rs
index 210f7ce2079b..2e066350d18d 100644
--- a/crates/cranelift/src/translate/code_translator.rs
+++ b/crates/cranelift/src/translate/code_translator.rs
@@ -2755,6 +2755,34 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
             )?;
             state.push1(result);
         }
+        Operator::RefCastNonNull { hty } => {
+            let r = state.pop1();
+            let heap_type = environ.convert_heap_type(*hty);
+            let cast_okay = environ.translate_ref_test(
+                builder,
+                WasmRefType {
+                    heap_type,
+                    nullable: false,
+                },
+                r,
+            )?;
+            environ.trapz(builder, cast_okay, crate::TRAP_CAST_FAILURE);
+            state.push1(r);
+        }
+        Operator::RefCastNullable { hty } => {
+            let r = state.pop1();
+            let heap_type = environ.convert_heap_type(*hty);
+            let cast_okay = environ.translate_ref_test(
+                builder,
+                WasmRefType {
+                    heap_type,
+                    nullable: true,
+                },
+                r,
+            )?;
+            environ.trapz(builder, cast_okay, crate::TRAP_CAST_FAILURE);
+            state.push1(r);
+        }
         Operator::AnyConvertExtern => {
             // Pop an `externref`, push an `anyref`. But they have the same
             // representation, so we don't actually need to do anything.
@@ -2764,10 +2792,7 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
             // representation, so we don't actually need to do anything.
         }
 
-        Operator::RefCastNonNull { .. }
-        | Operator::RefCastNullable { .. }
-        | Operator::BrOnCast { .. }
-        | Operator::BrOnCastFail { .. } => {
+        Operator::BrOnCast { .. } | Operator::BrOnCastFail { .. } => {
             return Err(wasm_unsupported!("GC operator not yet implemented: {op:?}"));
         }
 
diff --git a/crates/environ/src/trap_encoding.rs b/crates/environ/src/trap_encoding.rs
index ce5c4af21283..6c08471fd7ca 100644
--- a/crates/environ/src/trap_encoding.rs
+++ b/crates/environ/src/trap_encoding.rs
@@ -80,6 +80,9 @@ pub enum Trap {
     /// Attempted an allocation that was too large to succeed.
     AllocationTooLarge,
 
+    /// Attempted to cast a reference to a type that it is not an instance of.
+    CastFailure,
+
     /// When the `component-model` feature is enabled this trap represents a
     /// scenario where one component tried to call another component but it
     /// would have violated the reentrance rules of the component model,
@@ -119,6 +122,7 @@ impl Trap {
             NullReference
             ArrayOutOfBounds
             AllocationTooLarge
+            CastFailure
             CannotEnterComponent
         }
 
@@ -148,6 +152,7 @@ impl fmt::Display for Trap {
             NullReference => "null reference",
             ArrayOutOfBounds => "out of bounds array access",
             AllocationTooLarge => "allocation size too large",
+            CastFailure => "cast failure",
             CannotEnterComponent => "cannot enter component instance",
         };
         write!(f, "wasm trap: {desc}")
diff --git a/tests/wast.rs b/tests/wast.rs
index ec95ffb3ba16..d3cd7d24761d 100644
--- a/tests/wast.rs
+++ b/tests/wast.rs
@@ -207,14 +207,12 @@ fn should_fail(test: &Path, strategy: Strategy) -> bool {
         "binary_gc.wast",
         "br_on_cast_fail.wast",
         "br_on_cast.wast",
-        "ref_cast.wast",
         "table_sub.wast",
         "type_canon.wast",
         "type_equivalence.wast",
         "type-rec.wast",
         "type-subtyping.wast",
         "unreached_valid.wast",
-        "i31.wast",
     ];
 
     for part in test.iter() {