[NFC] OptimizeAddedConstants: Early exit if there are no memories (#6926)

The pass optimizes loads and stores, so without a memory there is nothing to
do.

This only helps if the user set --low-memory-unused and also has no memory,
which is likely rare, but it's a trivial change so it seems worthwhile. In particular
this pass constructs a LocalGraph, so if we can avoid work it can be substantial.

2 files changed, 26 insertions, 0 deletions

diff --git a/src/passes/OptimizeAddedConstants.cpp b/src/passes/OptimizeAddedConstants.cpp
index c76711d8a..f03109223 100644
--- a/src/passes/OptimizeAddedConstants.cpp
+++ b/src/passes/OptimizeAddedConstants.cpp
@@ -290,6 +290,11 @@ struct OptimizeAddedConstants
               << "--low-memory-unused flag is set.";
     }
 
+    if (getModule()->memories.empty()) {
+      // There can be no loads and stores without a memory.
+      return;
+    }
+
     // Multiple passes may be needed if we have x + 4 + 8 etc. (nested structs
     // in C can cause this, but it's rare). Note that we only need that for the
     // propagation case (as 4 + 8 would be optimized directly if it were
diff --git a/test/lit/passes/optimize-added-constants-nomemory.wast b/test/lit/passes/optimize-added-constants-nomemory.wast
new file mode 100644
index 000000000..75b9e112c
--- /dev/null
+++ b/test/lit/passes/optimize-added-constants-nomemory.wast
@@ -0,0 +1,21 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; RUN: wasm-opt %s -all --optimize-added-constants --low-memory-unused -S -o - | filecheck %s
+
+;; Check we do not error on modules with no memories, which the pass has
+;; nothing to do on.
+
+(module
+  ;; CHECK:      (func $do-stuff-without-a-memory (type $0) (param $x i32) (result i32)
+  ;; CHECK-NEXT:  (i32.add
+  ;; CHECK-NEXT:   (local.get $x)
+  ;; CHECK-NEXT:   (i32.const 42)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $do-stuff-without-a-memory (param $x i32) (result i32)
+    (i32.add
+      (local.get $x)
+      (i32.const 42)
+    )
+  )
+)