loads may trap, do not remove them in vacuum unless the pass options allow that

1 files changed, 3 insertions, 1 deletions

diff --git a/src/passes/Vacuum.cpp b/src/passes/Vacuum.cpp
index b58bea4b3..70230e502 100644
--- a/src/passes/Vacuum.cpp
+++ b/src/passes/Vacuum.cpp
@@ -73,7 +73,9 @@ struct Vacuum : public WalkerPass<PostWalker<Vacuum>> {
         case Expression::Id::UnreachableId: return curr; // always needed
 
         case Expression::Id::LoadId: {
-          if (!resultUsed) {
+          // it is ok to remove a load if the result is not used, and it has no
+          // side effects (the load itself may trap, if we are not ignoring such things)
+          if (!resultUsed && !EffectAnalyzer(getPassOptions(), curr).hasSideEffects()) {
             return curr->cast<Load>()->ptr;
           }
           return curr;