improve dce to handle more cases of nested unreachable code (#989)

* improve dce to handle more cases of nested unreachable code, in particular, when the child is unreachable in type but not an actual Unreachable node, e.g. if it's a br. in that case, we just need to verify that the br is not to us where we are a block or loop

* handle unreachable switch conditions in dce

* handle dce of br condition which is unreachable, and host arguments

* handle dce of block i32 etc. which is actually unreachable

1 files changed, 6 insertions, 1 deletions

diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index a983fc943..36eff681f 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -409,7 +409,12 @@ void Host::finalize() {
       break;
     }
     case GrowMemory: {
-      type = i32;
+      // if the single operand is not reachable, so are we
+      if (operands[0]->type == unreachable) {
+        type = unreachable;
+      } else {
+        type = i32;
+      }
       break;
     }
     default: abort();