avoid signed overflow undefined behavior in OptimizeInstructions constant computations (#1990)

2 files changed, 8 insertions, 2 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 7d4735686..c098d0ed7 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -825,11 +825,11 @@ private:
   // find added constants in an expression tree, including multiplied/shifted, and combine them
   // note that we ignore division/shift-right, as rounding makes this nonlinear, so not a valid opt
   Expression* optimizeAddedConstants(Binary* binary) {
-    int32_t constant = 0;
+    uint32_t constant = 0;
     std::vector<Const*> constants;
     std::function<void (Expression*, int)> seek = [&](Expression* curr, int mul) {
       if (auto* c = curr->dynCast<Const>()) {
-        auto value = c->value.geti32();
+        uint32_t value = c->value.geti32();
         if (value != 0) {
           constant += value * mul;
           constants.push_back(c);
diff --git a/test/passes/O1.wast b/test/passes/O1.wast
index 87b06b063..6c1f3abda 100644
--- a/test/passes/O1.wast
+++ b/test/passes/O1.wast
@@ -14,6 +14,12 @@
    )
   )
  )
+ (func $signed-overflow (param $0 f32) (result i32)
+  (i32.sub
+   (i32.const 268435456)
+   (i32.const -2147483648)
+  )
+ )
 )