[Wasm GC] Fix StructSet::finalize on an unreachable value (#3874)

Also fix printing of unreachable StructSets, which must handle the case
of an unreachable reference, which means we do not know the RTT,
and so we must print a replacement for the StructSet somehow. Emit a
block with drops, fixing the old behavior which was missing the drops.

6 files changed, 98 insertions, 19 deletions

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 1392ccb6f..ef78bf582 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -1926,7 +1926,7 @@ struct PrintExpressionContents
     // where if the ref is unreachable, we don't know what heap type to print),
     // then print the children in a block, which is good enough as this
     // instruction is never reached anyhow.
-    printMedium(o, "block ");
+    printMedium(o, "block");
   }
   void printFieldName(HeapType type, Index index) {
     processFieldName(wasm, type, index, [&](Name name) {
@@ -2346,6 +2346,33 @@ struct PrintSExpression : public UnifiedExpressionVisitor<PrintSExpression> {
       o << " ;; end try";
     }
   }
+  void printUnreachableReplacement(Expression* curr) {
+    // See the parallel function in PrintExpressionContents for background.
+    //
+    // Emit a block with drops of the children.
+    o << "(block";
+    incIndent();
+    for (auto* child : ChildIterator(curr)) {
+      Drop drop;
+      drop.value = child;
+      printFullLine(&drop);
+    }
+    decIndent();
+  }
+  void visitStructSet(StructSet* curr) {
+    if (curr->ref->type == Type::unreachable) {
+      printUnreachableReplacement(curr);
+      return;
+    }
+    visitExpression(curr);
+  }
+  void visitStructGet(StructGet* curr) {
+    if (curr->ref->type == Type::unreachable) {
+      printUnreachableReplacement(curr);
+      return;
+    }
+    visitExpression(curr);
+  }
   // Module-level visitors
   void handleSignature(Signature curr, Name name = Name()) {
     o << "(func";
diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index 410ba0573..69464e73f 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -977,7 +977,7 @@ void StructGet::finalize() {
 }
 
 void StructSet::finalize() {
-  if (ref->type == Type::unreachable) {
+  if (ref->type == Type::unreachable || value->type == Type::unreachable) {
     type = Type::unreachable;
   } else {
     type = Type::none;
diff --git a/test/heap-types.wast b/test/heap-types.wast
index e932df82f..da22cc7d9 100644
--- a/test/heap-types.wast
+++ b/test/heap-types.wast
@@ -258,12 +258,18 @@
       )
     )
   )
-  (func $unreachables
+  (func $unreachables-1
     (drop
-      (struct.get $struct.A 0 (unreachable))
-    )
-    (drop
-      (struct.set $struct.A 0 (unreachable) (unreachable))
+      (struct.get $struct.C 0 (unreachable))
     )
   )
+  (func $unreachables-2
+    (struct.set $struct.C 0 (ref.null $struct.C) (unreachable))
+  )
+  (func $unreachables-3
+    (struct.set $struct.C 0 (unreachable) (unreachable))
+  )
+  (func $unreachables-4
+    (struct.set $struct.C 0 (unreachable) (f32.const 1))
+  )
 )
diff --git a/test/heap-types.wast.from-wast b/test/heap-types.wast.from-wast
index 4fbf5026c..fbbc47af9 100644
--- a/test/heap-types.wast.from-wast
+++ b/test/heap-types.wast.from-wast
@@ -1,14 +1,14 @@
 (module
  (type $struct.A (struct (field i32) (field f32) (field $named f64)))
  (type $struct.B (struct (field i8) (field (mut i16)) (field (ref $struct.A)) (field (mut (ref $struct.A)))))
+ (type $none_=>_none (func))
  (type $grandchild (struct (field i32) (field i64)))
+ (type $struct.C (struct (field $named-mut (mut f32))))
  (type $vector (array (mut f64)))
  (type $matrix (array (mut (ref null $vector))))
  (type $anyref_=>_none (func (param anyref)))
  (type $parent (struct ))
  (type $child (struct (field i32)))
- (type $struct.C (struct (field $named-mut (mut f32))))
- (type $none_=>_none (func))
  (type $nested-child-struct (struct (field (mut (ref $child)))))
  (type $rtt_1_$parent_=>_none (func (param (rtt 1 $parent))))
  (type $rtt_$parent_=>_none (func (param (rtt $parent))))
@@ -307,17 +307,39 @@
    )
   )
  )
- (func $unreachables
+ (func $unreachables-1
   (drop
-   (block 
-    (unreachable)
+   (block
+    (drop
+     (unreachable)
+    )
    )
   )
-  (drop
-   (block 
+ )
+ (func $unreachables-2
+  (struct.set $struct.C $named-mut
+   (ref.null $struct.C)
+   (unreachable)
+  )
+ )
+ (func $unreachables-3
+  (block
+   (drop
+    (unreachable)
+   )
+   (drop
     (unreachable)
+   )
+  )
+ )
+ (func $unreachables-4
+  (block
+   (drop
     (unreachable)
    )
+   (drop
+    (f32.const 1)
+   )
   )
  )
 )
diff --git a/test/heap-types.wast.fromBinary b/test/heap-types.wast.fromBinary
index 65c04bd32..4ee4be42a 100644
--- a/test/heap-types.wast.fromBinary
+++ b/test/heap-types.wast.fromBinary
@@ -1,14 +1,14 @@
 (module
  (type $struct.A (struct (field i32) (field f32) (field $named f64)))
  (type $struct.B (struct (field i8) (field (mut i16)) (field (ref $struct.A)) (field (mut (ref $struct.A)))))
+ (type $none_=>_none (func))
  (type $grandchild (struct (field i32) (field i64)))
  (type $vector (array (mut f64)))
  (type $matrix (array (mut (ref null $vector))))
+ (type $struct.C (struct (field $named-mut (mut f32))))
  (type $anyref_=>_none (func (param anyref)))
  (type $parent (struct ))
  (type $child (struct (field i32)))
- (type $struct.C (struct (field $named-mut (mut f32))))
- (type $none_=>_none (func))
  (type $nested-child-struct (struct (field (mut (ref $child)))))
  (type $rtt_1_$parent_=>_none (func (param (rtt 1 $parent))))
  (type $rtt_$parent_=>_none (func (param (rtt $parent))))
@@ -306,7 +306,19 @@
    )
   )
  )
- (func $unreachables
+ (func $unreachables-1
+  (unreachable)
+ )
+ (func $unreachables-2
+  (drop
+   (ref.null $struct.C)
+  )
+  (unreachable)
+ )
+ (func $unreachables-3
+  (unreachable)
+ )
+ (func $unreachables-4
   (unreachable)
  )
 )
diff --git a/test/heap-types.wast.fromBinary.noDebugInfo b/test/heap-types.wast.fromBinary.noDebugInfo
index 2a0156000..525e265a4 100644
--- a/test/heap-types.wast.fromBinary.noDebugInfo
+++ b/test/heap-types.wast.fromBinary.noDebugInfo
@@ -1,14 +1,14 @@
 (module
  (type ${i32_f32_f64} (struct (field i32) (field f32) (field f64)))
  (type ${i8_mut:i16_ref|{i32_f32_f64}|_mut:ref|{i32_f32_f64}|} (struct (field i8) (field (mut i16)) (field (ref ${i32_f32_f64})) (field (mut (ref ${i32_f32_f64})))))
+ (type $none_=>_none (func))
  (type ${i32_i64} (struct (field i32) (field i64)))
  (type $[mut:f64] (array (mut f64)))
  (type $[mut:ref?|[mut:f64]|] (array (mut (ref null $[mut:f64]))))
+ (type ${mut:f32} (struct (field (mut f32))))
  (type $anyref_=>_none (func (param anyref)))
  (type ${} (struct ))
  (type ${i32} (struct (field i32)))
- (type ${mut:f32} (struct (field (mut f32))))
- (type $none_=>_none (func))
  (type ${mut:ref|{i32}|} (struct (field (mut (ref ${i32})))))
  (type $rtt_1_{}_=>_none (func (param (rtt 1 ${}))))
  (type $rtt_{}_=>_none (func (param (rtt ${}))))
@@ -309,5 +309,17 @@
  (func $8
   (unreachable)
  )
+ (func $9
+  (drop
+   (ref.null ${mut:f32})
+  )
+  (unreachable)
+ )
+ (func $10
+  (unreachable)
+ )
+ (func $11
+  (unreachable)
+ )
 )