Fix a crash in MemoryPacking due to an unreachable pointer (#5623)

Previously, the pointer type for newly emitted instructions was determined by
the type of the destination pointer on a memory.init instruction, but that did
not take into account that the destination pointer may be unreachable. Properly
look up the pointer type on the memory instead to fix the problem.

Fixes #5620.

Author: tlively

src/passes/MemoryPacking.cpp

@@ -701,7 +701,7 @@ void MemoryPacking::createReplacements(Module* module,
 
       // Calculate dest, either as a const or as an addition to the dest local
       Expression* dest;
-      Type ptrType = init->dest->type;
+      Type ptrType = module->getMemory(init->memory)->indexType;
       if (auto* c = init->dest->dynCast<Const>()) {
         dest =
           builder.makeConstPtr(c->value.getInteger() + bytesWritten, ptrType);

test/lit/passes/memory-packing_all-features.wast

@@ -2347,3 +2347,45 @@
   )
  )
 )
+(module
+ ;; CHECK:      (type $none_=>_none (func))
+
+ ;; CHECK:      (global $__mem_segment_drop_state (mut i32) (i32.const 0))
+
+ ;; CHECK:      (memory $0 1 1)
+ (memory $0 i32 1 1)
+ (data "\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00test")
+ ;; CHECK:      (data $0 "test")
+
+ ;; CHECK:      (func $0 (type $none_=>_none)
+ ;; CHECK-NEXT:  (local $0 i32)
+ ;; CHECK-NEXT:  (local.tee $0
+ ;; CHECK-NEXT:   (unreachable)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (if
+ ;; CHECK-NEXT:   (global.get $__mem_segment_drop_state)
+ ;; CHECK-NEXT:   (unreachable)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (memory.fill
+ ;; CHECK-NEXT:   (local.get $0)
+ ;; CHECK-NEXT:   (i32.const 0)
+ ;; CHECK-NEXT:   (i32.const 57)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (memory.init $0
+ ;; CHECK-NEXT:   (i32.add
+ ;; CHECK-NEXT:    (local.get $0)
+ ;; CHECK-NEXT:    (i32.const 57)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (i32.const 0)
+ ;; CHECK-NEXT:   (i32.const 4)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $0
+  ;; test that unreachable destinations are ok
+  (memory.init 0
+   (unreachable)
+   (i32.const 0)
+   (i32.const 61)
+  )
+ )
+)