3 files changed, 51 insertions, 0 deletions
diff --git a/src/passes/PickLoadSigns.cpp b/src/passes/PickLoadSigns.cpp
index c3b5a2ba2..3541b1055 100644
--- a/src/passes/PickLoadSigns.cpp
+++ b/src/passes/PickLoadSigns.cpp
@@ -109,6 +109,10 @@ struct PickLoadSigns : public WalkerPass<ExpressionStackWalker<PickLoadSigns>> {
              load->bytes * 8)) { // unsigned usages exist but the wrong size
         continue;
       }
+      // Atomic operations are always unsigned, never signed.
+      if (load->isAtomic) {
+        continue;
+      }
       // we can pick the optimal one. our hope is to remove 2 items per
       // signed use (two shifts), so we factor that in
       load->signed_ = usage.signedUsages * 2 >= usage.unsignedUsages;
diff --git a/test/passes/pick-load-signs_all-features.txt b/test/passes/pick-load-signs_all-features.txt
new file mode 100644
index 000000000..4b08c75de
--- /dev/null
+++ b/test/passes/pick-load-signs_all-features.txt
@@ -0,0 +1,24 @@
+(module
+ (type $none_=>_i32 (func (result i32)))
+ (memory $0 (shared 16 16))
+ (func $atomics-are-always-unsigned (result i32)
+  (local $0 i32)
+  (drop
+   (block $block (result i32)
+    (local.set $0
+     (i32.atomic.load16_u
+      (i32.const 27)
+     )
+    )
+    (i32.shr_s
+     (i32.shl
+      (local.get $0)
+      (i32.const 16)
+     )
+     (i32.const 16)
+    )
+   )
+  )
+  (i32.const -65)
+ )
+)
diff --git a/test/passes/pick-load-signs_all-features.wast b/test/passes/pick-load-signs_all-features.wast
new file mode 100644
index 000000000..20a77eae4
--- /dev/null
+++ b/test/passes/pick-load-signs_all-features.wast
@@ -0,0 +1,23 @@
+(module
+ (memory $0 (shared 16 16))
+ (func $atomics-are-always-unsigned (result i32)
+  (local $0 i32)
+  (drop
+   (block (result i32)
+    (local.set $0
+     (i32.atomic.load16_u ;; an atomic load cannot become signed
+      (i32.const 27)
+     )
+    )
+    (i32.shr_s
+     (i32.shl
+      (local.get $0)
+      (i32.const 16)
+     )
+     (i32.const 16)
+    )
+   )
+  )
+  (i32.const -65)
+ )
+)