[NFC] Avoid wasted LocalGraph work in MergeLocals (#6908)

We computed both get and set influences, but getGetInfluences() was
never called, so that work was entirely pointless.

This makes the pass 20% faster.

2 files changed, 31 insertions, 1 deletions

diff --git a/src/passes/MergeLocals.cpp b/src/passes/MergeLocals.cpp
index e6cf71538..9402e0669 100644
--- a/src/passes/MergeLocals.cpp
+++ b/src/passes/MergeLocals.cpp
@@ -108,7 +108,7 @@ struct MergeLocals
     // compute all dependencies
     auto* func = getFunction();
     LocalGraph preGraph(func, getModule());
-    preGraph.computeInfluences();
+    preGraph.computeSetInfluences();
     // optimize each copy
     std::unordered_map<LocalSet*, LocalSet*> optimizedToCopy,
       optimizedToTrivial;
diff --git a/test/lit/passes/merge-locals.wast b/test/lit/passes/merge-locals.wast
new file mode 100644
index 000000000..0b1e45d9d
--- /dev/null
+++ b/test/lit/passes/merge-locals.wast
@@ -0,0 +1,30 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; RUN: wasm-opt %s --merge-locals -all -S -o - | filecheck %s
+
+(module
+  ;; CHECK:      (func $between-unreachable (type $0) (result i32)
+  ;; CHECK-NEXT:  (local $x i32)
+  ;; CHECK-NEXT:  (local $y i32)
+  ;; CHECK-NEXT:  (select
+  ;; CHECK-NEXT:   (unreachable)
+  ;; CHECK-NEXT:   (local.tee $x
+  ;; CHECK-NEXT:    (local.get $y)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (unreachable)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $between-unreachable (result i32)
+    (local $x i32)
+    (local $y i32)
+    (select
+      (unreachable)
+      ;; The local copy here is in between unreachables. We should not error.
+      (local.tee $x
+        (local.get $y)
+      )
+      (unreachable)
+    )
+  )
+)
+