zero shifts are not sign-extends

Author: kripken

src/ast/properties.h

@@ -60,11 +60,13 @@ struct Properties {
     if (auto* outer = curr->dynCast<Binary>()) {
       if (outer->op == ShrSInt32) {
         if (auto* outerConst = outer->right->dynCast<Const>()) {
-          if (auto* inner = outer->left->dynCast<Binary>()) {
-            if (inner->op == ShlInt32) {
-              if (auto* innerConst = inner->right->dynCast<Const>()) {
-                if (outerConst->value == innerConst->value) {
-                  return inner->left;
+          if (outerConst->value.geti32() != 0) {
+            if (auto* inner = outer->left->dynCast<Binary>()) {
+              if (inner->op == ShlInt32) {
+                if (auto* innerConst = inner->right->dynCast<Const>()) {
+                  if (outerConst->value == innerConst->value) {
+                    return inner->left;
+                  }
                 }
               }
             }
@@ -87,11 +89,13 @@ struct Properties {
     if (auto* outer = curr->dynCast<Binary>()) {
       if (outer->op == ShrSInt32) {
         if (auto* outerConst = outer->right->dynCast<Const>()) {
-          if (auto* inner = outer->left->dynCast<Binary>()) {
-            if (inner->op == ShlInt32) {
-              if (auto* innerConst = inner->right->dynCast<Const>()) {
-                if (outerConst->value.leU(innerConst->value).geti32()) {
-                  return inner->left;
+          if (outerConst->value.geti32() != 0) {
+            if (auto* inner = outer->left->dynCast<Binary>()) {
+              if (inner->op == ShlInt32) {
+                if (auto* innerConst = inner->right->dynCast<Const>()) {
+                  if (outerConst->value.leU(innerConst->value).geti32()) {
+                    return inner->left;
+                  }
                 }
               }
             }

test/passes/optimize-instructions.txt

@@ -1962,4 +1962,34 @@
    )
   )
  )
+ (func $zero-shifts-is-not-sign-ext (type $1)
+  (drop
+   (i32.eq
+    (i32.shr_s
+     (i32.shl
+      (i32.load16_s align=1
+       (i32.const 790656516)
+      )
+      (i32.const 0)
+     )
+     (i32.const 0)
+    )
+    (i32.const -5431187)
+   )
+  )
+  (drop
+   (i32.eq
+    (i32.shr_s
+     (i32.shl
+      (i32.load16_s align=1
+       (i32.const 790656516)
+      )
+      (i32.const 1)
+     )
+     (i32.const 0)
+    )
+    (i32.const -5431187)
+   )
+  )
+ )
 )

test/passes/optimize-instructions.wast

@@ -2359,4 +2359,40 @@
       )
     )
   )
+  (func $zero-shifts-is-not-sign-ext
+   (drop
+    (i32.eq
+     (i32.const -5431187)
+     (i32.add
+      (i32.const 0)
+      (i32.shr_s
+       (i32.shl
+        (i32.load16_s align=1
+         (i32.const 790656516)
+        )
+        (i32.const 0)
+       )
+       (i32.const 0)
+      )
+     )
+    )
+   )
+   (drop
+    (i32.eq
+     (i32.const -5431187)
+     (i32.add
+      (i32.const 0)
+      (i32.shr_s
+       (i32.shl
+        (i32.load16_s align=1
+         (i32.const 790656516)
+        )
+        (i32.const 1)
+       )
+       (i32.const 0)
+      )
+     )
+    )
+   )
+  )
 )