do not combine a load/store offset with a constant pointer if it would wrap a negative value to a positive one, as trapping is tricky

1 files changed, 9 insertions, 2 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index de6f96ccc..2930fe9c9 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -908,8 +908,15 @@ private:
     // it's better to do the opposite for gzip purposes as well as for readability.
     auto* last = ptr->dynCast<Const>();
     if (last) {
-      last->value = Literal(int32_t(last->value.geti32() + offset));
-      offset = 0;
+      // don't do this if it would wrap the pointer
+      uint64_t value64 = last->value.geti32();
+      uint64_t offset64 = offset;
+      if (value64 <= std::numeric_limits<int32_t>::max() &&
+          offset64 <= std::numeric_limits<int32_t>::max() &&
+          value64 + offset64 <= std::numeric_limits<int32_t>::max()) {
+        last->value = Literal(int32_t(value64 + offset64));
+        offset = 0;
+      }
     }
   }