diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 9ea8a7aa982..ac1552ee0c7 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -1193,6 +1193,35 @@ struct OptimizeInstructions
           BranchHints::flip(curr, getFunction());
         }
       }
+      // (i32.and X 1) as if-else condition =>  (i32.ctz X) with swapped arms,
+      // since ctz(X) == 0  iff  LSB(X) == 1  (saves one instruction).
+      //
+      // Gated on shrinkLevel >= 1 (i.e. -Os or -Oz) only: TZCNT can cost
+      // 1-2 cycles more than AND on common JIT VMs (per Agner Fog's
+      // tables), and JIT-less interpreters (wasm3, smart-contract
+      // runtimes) lack a fast path for ctz at all. The byte-saving is the
+      // win we want under shrink modes; under speed modes the AND form
+      // stays. See WebAssembly/binaryen#8562.
+      if (auto* binary = curr->condition->dynCast<Binary>()) {
+        if (binary->op == AndInt32 && getPassOptions().shrinkLevel >= 1) {
+          Expression* other = nullptr;
+          if (auto* c = binary->right->dynCast<Const>()) {
+            if (c->value.geti32() == 1) {
+              other = binary->left;
+            }
+          } else if (auto* c = binary->left->dynCast<Const>()) {
+            if (c->value.geti32() == 1) {
+              other = binary->right;
+            }
+          }
+          if (other) {
+            Builder builder(*getModule());
+            curr->condition = builder.makeUnary(CtzInt32, other);
+            std::swap(curr->ifTrue, curr->ifFalse);
+            BranchHints::flip(curr, getFunction());
+          }
+        }
+      }
       // Note that we do not consider metadata here. Like LLVM, we ignore
       // metadata when trying to fold code together, preferring certain
       // optimization over possible benefits of profiling data.
@@ -3114,6 +3143,27 @@ struct OptimizeInstructions
               binary->op = op;
               return binary;
             }
+            // eqz(and X 1) ==> ctz X  in boolean context:
+            // both are truthy iff LSB(X) == 0, saving one instruction.
+            // Gated on shrinkLevel >= 1 (-Os, -Oz) — see the matching
+            // comment in visitIf and WebAssembly/binaryen#8562.
+            if (binary->op == AndInt32 &&
+                getPassOptions().shrinkLevel >= 1) {
+              Expression* other = nullptr;
+              if (auto* c = binary->right->dynCast<Const>()) {
+                if (c->value.geti32() == 1) {
+                  other = binary->left;
+                }
+              } else if (auto* c = binary->left->dynCast<Const>()) {
+                if (c->value.geti32() == 1) {
+                  other = binary->right;
+                }
+              }
+              if (other) {
+                Builder builder(*getModule());
+                return builder.makeUnary(CtzInt32, other);
+              }
+            }
           }
         }
         if (unary->op == EqZInt32 || unary->op == EqZInt64) {
diff --git a/test/lit/passes/optimize-instructions-lsb-if.wast b/test/lit/passes/optimize-instructions-lsb-if.wast
new file mode 100644
index 00000000000..89c24a7b270
--- /dev/null
+++ b/test/lit/passes/optimize-instructions-lsb-if.wast
@@ -0,0 +1,186 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --optimize-instructions -S -o -                  | filecheck %s --check-prefix=DEFAULT
+;; RUN: wasm-opt %s --shrink-level=1 --optimize-instructions -S -o - | filecheck %s --check-prefix=SHRINK
+
+;; Test the LSB→ctz fold: under shrink modes (-Os, -Oz, equivalent to
+;; --shrink-level >= 1) `(if (i32.and X 1) T E)` becomes
+;; `(if (i32.ctz X) E T)`, and `(br_if N V (i32.eqz (i32.and X 1)))`
+;; becomes `(br_if N V (i32.ctz X))` — one instruction less, but
+;; potentially 1-2 cycles slower on JIT VMs and unconditionally slower
+;; on JIT-less interpreters. The fold is therefore suppressed under
+;; default and speed-optimised modes, and only fires when the user has
+;; opted into shrinking. See WebAssembly/binaryen#8562.
+
+(module
+  ;; DEFAULT:      (func $lsb-if (param $x i32) (result i32)
+  ;; DEFAULT-NEXT:  (if (result i32)
+  ;; DEFAULT-NEXT:   (i32.and
+  ;; DEFAULT-NEXT:    (local.get $x)
+  ;; DEFAULT-NEXT:    (i32.const 1)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:   (then
+  ;; DEFAULT-NEXT:    (i32.const 1)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:   (else
+  ;; DEFAULT-NEXT:    (i32.const 0)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:  )
+  ;; DEFAULT-NEXT: )
+  ;; SHRINK:      (func $lsb-if (param $x i32) (result i32)
+  ;; SHRINK-NEXT:  (if (result i32)
+  ;; SHRINK-NEXT:   (i32.ctz
+  ;; SHRINK-NEXT:    (local.get $x)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:   (then
+  ;; SHRINK-NEXT:    (i32.const 0)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:   (else
+  ;; SHRINK-NEXT:    (i32.const 1)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:  )
+  ;; SHRINK-NEXT: )
+  (func $lsb-if (param $x i32) (result i32)
+    ;; if LSB is set, return 1; else return 0
+    (if (result i32)
+      (i32.and (local.get $x) (i32.const 1))
+      (then (i32.const 1))
+      (else (i32.const 0))
+    )
+  )
+
+  ;; DEFAULT:      (func $lsb-if-const-left (param $x i32) (result i32)
+  ;; DEFAULT-NEXT:  (if (result i32)
+  ;; DEFAULT-NEXT:   (i32.and
+  ;; DEFAULT-NEXT:    (local.get $x)
+  ;; DEFAULT-NEXT:    (i32.const 1)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:   (then
+  ;; DEFAULT-NEXT:    (i32.const 1)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:   (else
+  ;; DEFAULT-NEXT:    (i32.const 0)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:  )
+  ;; DEFAULT-NEXT: )
+  ;; SHRINK:      (func $lsb-if-const-left (param $x i32) (result i32)
+  ;; SHRINK-NEXT:  (if (result i32)
+  ;; SHRINK-NEXT:   (i32.ctz
+  ;; SHRINK-NEXT:    (local.get $x)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:   (then
+  ;; SHRINK-NEXT:    (i32.const 0)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:   (else
+  ;; SHRINK-NEXT:    (i32.const 1)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:  )
+  ;; SHRINK-NEXT: )
+  (func $lsb-if-const-left (param $x i32) (result i32)
+    ;; same but constant on the left
+    (if (result i32)
+      (i32.and (i32.const 1) (local.get $x))
+      (then (i32.const 1))
+      (else (i32.const 0))
+    )
+  )
+
+  ;; DEFAULT:      (func $lsb-brif (param $x i32) (result i32)
+  ;; DEFAULT-NEXT:  (block $done (result i32)
+  ;; DEFAULT-NEXT:   (drop
+  ;; DEFAULT-NEXT:    (br_if $done
+  ;; DEFAULT-NEXT:     (i32.const 99)
+  ;; DEFAULT-NEXT:     (i32.eqz
+  ;; DEFAULT-NEXT:      (i32.and
+  ;; DEFAULT-NEXT:       (local.get $x)
+  ;; DEFAULT-NEXT:       (i32.const 1)
+  ;; DEFAULT-NEXT:      )
+  ;; DEFAULT-NEXT:     )
+  ;; DEFAULT-NEXT:    )
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:   (i32.const 42)
+  ;; DEFAULT-NEXT:  )
+  ;; DEFAULT-NEXT: )
+  ;; SHRINK:      (func $lsb-brif (param $x i32) (result i32)
+  ;; SHRINK-NEXT:  (block $done (result i32)
+  ;; SHRINK-NEXT:   (drop
+  ;; SHRINK-NEXT:    (br_if $done
+  ;; SHRINK-NEXT:     (i32.const 99)
+  ;; SHRINK-NEXT:     (i32.ctz
+  ;; SHRINK-NEXT:      (local.get $x)
+  ;; SHRINK-NEXT:     )
+  ;; SHRINK-NEXT:    )
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:   (i32.const 42)
+  ;; SHRINK-NEXT:  )
+  ;; SHRINK-NEXT: )
+  (func $lsb-brif (param $x i32) (result i32)
+    ;; br_if (eqz (and X 1)) — the typical is_skewed/is_scalar pattern
+    (block $done (result i32)
+      (drop
+        (br_if $done
+          (i32.const 99)
+          (i32.eqz (i32.and (local.get $x) (i32.const 1)))
+        )
+      )
+      (i32.const 42)
+    )
+  )
+
+  ;; DEFAULT:      (func $lsb-select (param $x i32) (param $a i32) (param $b i32) (result i32)
+  ;; DEFAULT-NEXT:  (select
+  ;; DEFAULT-NEXT:   (local.get $b)
+  ;; DEFAULT-NEXT:   (local.get $a)
+  ;; DEFAULT-NEXT:   (i32.and
+  ;; DEFAULT-NEXT:    (local.get $x)
+  ;; DEFAULT-NEXT:    (i32.const 1)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:  )
+  ;; DEFAULT-NEXT: )
+  ;; SHRINK:      (func $lsb-select (param $x i32) (param $a i32) (param $b i32) (result i32)
+  ;; SHRINK-NEXT:  (select
+  ;; SHRINK-NEXT:   (local.get $a)
+  ;; SHRINK-NEXT:   (local.get $b)
+  ;; SHRINK-NEXT:   (i32.ctz
+  ;; SHRINK-NEXT:    (local.get $x)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:  )
+  ;; SHRINK-NEXT: )
+  (func $lsb-select (param $x i32) (param $a i32) (param $b i32) (result i32)
+    ;; select with the eqz-and-1 boolean condition.
+    ;; Non-constant arms keep the select itself in the IR — otherwise
+    ;; an unrelated `select c1 c0 P` simplification would eat it.
+    (select
+      (local.get $a)
+      (local.get $b)
+      (i32.eqz (i32.and (local.get $x) (i32.const 1)))
+    )
+  )
+
+  ;; DEFAULT:      (func $lsb-select-const-left (param $x i32) (param $a i32) (param $b i32) (result i32)
+  ;; DEFAULT-NEXT:  (select
+  ;; DEFAULT-NEXT:   (local.get $b)
+  ;; DEFAULT-NEXT:   (local.get $a)
+  ;; DEFAULT-NEXT:   (i32.and
+  ;; DEFAULT-NEXT:    (local.get $x)
+  ;; DEFAULT-NEXT:    (i32.const 1)
+  ;; DEFAULT-NEXT:   )
+  ;; DEFAULT-NEXT:  )
+  ;; DEFAULT-NEXT: )
+  ;; SHRINK:      (func $lsb-select-const-left (param $x i32) (param $a i32) (param $b i32) (result i32)
+  ;; SHRINK-NEXT:  (select
+  ;; SHRINK-NEXT:   (local.get $a)
+  ;; SHRINK-NEXT:   (local.get $b)
+  ;; SHRINK-NEXT:   (i32.ctz
+  ;; SHRINK-NEXT:    (local.get $x)
+  ;; SHRINK-NEXT:   )
+  ;; SHRINK-NEXT:  )
+  ;; SHRINK-NEXT: )
+  (func $lsb-select-const-left (param $x i32) (param $a i32) (param $b i32) (result i32)
+    ;; same but with the constant on the left of the AND.
+    (select
+      (local.get $a)
+      (local.get $b)
+      (i32.eqz (i32.and (i32.const 1) (local.get $x)))
+    )
+  )
+)