[Optimize Instructions] Simplify zero/sign extentions (special case) (#4009)

For signed or unsigned extension to 64-bits after lowering from partially filled 64-bit arguments:
```rust
i64.extend_i32_u(i32.wrap_i64(x))  =>  x   // where maxBits(x) <= 32
i64.extend_i32_s(i32.wrap_i64(x))  =>  x   // where maxBits(x) <= 31
```

1 files changed, 25 insertions, 9 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 31ed9348a..2e6a2d48d 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -841,19 +841,35 @@ struct OptimizeInstructions
         }
       }
       {
-        Unary* inner;
+        // i64.extend_i32_s(i32.wrap_i64(x))  =>  x
+        //   where maxBits(x) <= 31
+        //
+        // i64.extend_i32_u(i32.wrap_i64(x))  =>  x
+        //   where maxBits(x) <= 32
         Expression* x;
-        if (getModule()->features.hasSignExt()) {
-          // i64.extend_i32_s(i32.wrap_i64(x))  =>  i64.extend32_s(x)
-          if (matches(curr,
-                      unary(ExtendSInt32, unary(&inner, WrapInt64, any(&x))))) {
-            inner->op = ExtendS32Int64;
-            inner->type = Type::i64;
-            inner->value = x;
-            return replaceCurrent(inner);
+        UnaryOp unaryOp;
+        if (matches(curr, unary(&unaryOp, unary(WrapInt64, any(&x))))) {
+          if (unaryOp == ExtendSInt32 || unaryOp == ExtendUInt32) {
+            auto maxBits = Bits::getMaxBits(x, this);
+            if ((unaryOp == ExtendSInt32 && maxBits <= 31) ||
+                (unaryOp == ExtendUInt32 && maxBits <= 32)) {
+              return replaceCurrent(x);
+            }
           }
         }
       }
+      if (getModule()->features.hasSignExt()) {
+        // i64.extend_i32_s(i32.wrap_i64(x))  =>  i64.extend32_s(x)
+        Unary* inner;
+        Expression* x;
+        if (matches(curr,
+                    unary(ExtendSInt32, unary(&inner, WrapInt64, any(&x))))) {
+          inner->op = ExtendS32Int64;
+          inner->type = Type::i64;
+          inner->value = x;
+          return replaceCurrent(inner);
+        }
+      }
     }
 
     if (Abstract::hasAnyReinterpret(curr->op)) {