[GC] Do not crash on unreachable inputs to struct.get/set (#3542)

If the reference is unreachable then we cannot find the heap type to print
in the text format. Instead of crashing or emitting something invalid, print
a block instead - the block contains the children so they are emitted, and
as the instruction was unreachable anyhow, this has no noticeable effect.
It also parallels what we do in the binary format - skip unreachable code.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 67deac35c..b7b7e1320 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -1840,7 +1840,18 @@ struct PrintExpressionContents
     o << "with_rtt ";
     printHeapTypeName(o, curr->rtt->type.getHeapType());
   }
+  void printUnreachableReplacement() {
+    // If we cannot print a valid unreachable instruction (say, a struct.get,
+    // 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 ");
+  }
   void visitStructGet(StructGet* curr) {
+    if (curr->ref->type == Type::unreachable) {
+      printUnreachableReplacement();
+      return;
+    }
     const auto& field =
       curr->ref->type.getHeapType().getStruct().fields[curr->index];
     if (field.type == Type::i32 && field.packedType != Field::not_packed) {
@@ -1857,6 +1868,10 @@ struct PrintExpressionContents
     o << curr->index;
   }
   void visitStructSet(StructSet* curr) {
+    if (curr->ref->type == Type::unreachable) {
+      printUnreachableReplacement();
+      return;
+    }
     printMedium(o, "struct.set ");
     printHeapTypeName(o, curr->ref->type.getHeapType());
     o << ' ';