optimize out 0-x, a zero only used to negate an int, when possible (#1365)

12 files changed, 134 insertions, 48 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 06f3d5b02..efea99247 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -506,7 +506,43 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions,
           }
         }
         // note that both left and right may be consts, but then we let precompute compute the constant result
-      } else if (binary->op == AddInt32 || binary->op == SubInt32) {
+      } else if (binary->op == AddInt32) {
+        // try to get rid of (0 - ..), that is, a zero only used to negate an
+        // int. an add of a subtract can be flipped in order to remove it:
+        //   (i32.add
+        //     (i32.sub
+        //       (i32.const 0)
+        //       X
+        //     )
+        //     Y
+        //   )
+        // =>
+        //   (i32.sub
+        //     Y
+        //     X
+        //   )
+        if (auto* sub = binary->left->dynCast<Binary>()) {
+          if (sub->op == SubInt32) {
+            if (auto* subZero = sub->left->dynCast<Const>()) {
+              if (subZero->value.geti32() == 0) {
+                sub->left = binary->right;
+                return sub;
+              }
+            }
+          }
+        }
+        if (auto* sub = binary->right->dynCast<Binary>()) {
+          if (sub->op == SubInt32) {
+            if (auto* subZero = sub->left->dynCast<Const>()) {
+              if (subZero->value.geti32() == 0) {
+                sub->left = binary->left;
+                return sub;
+              }
+            }
+          }
+        }
+        return optimizeAddedConstants(binary);
+      } else if (binary->op == SubInt32) {
         return optimizeAddedConstants(binary);
       }
       // a bunch of operations on a constant right side can be simplified
diff --git a/test/emcc_O2_hello_world.fromasm b/test/emcc_O2_hello_world.fromasm
index 0bc4edf68..082240fc4 100644
--- a/test/emcc_O2_hello_world.fromasm
+++ b/test/emcc_O2_hello_world.fromasm
@@ -5966,12 +5966,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $11)
-         )
+         (get_local $11)
         )
        )
        (get_local $14)
diff --git a/test/emcc_O2_hello_world.fromasm.clamp b/test/emcc_O2_hello_world.fromasm.clamp
index 0bc4edf68..082240fc4 100644
--- a/test/emcc_O2_hello_world.fromasm.clamp
+++ b/test/emcc_O2_hello_world.fromasm.clamp
@@ -5966,12 +5966,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $11)
-         )
+         (get_local $11)
         )
        )
        (get_local $14)
diff --git a/test/emcc_O2_hello_world.fromasm.imprecise b/test/emcc_O2_hello_world.fromasm.imprecise
index 1fe0499f9..0bad341fb 100644
--- a/test/emcc_O2_hello_world.fromasm.imprecise
+++ b/test/emcc_O2_hello_world.fromasm.imprecise
@@ -5965,12 +5965,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $11)
-         )
+         (get_local $11)
         )
        )
        (get_local $14)
diff --git a/test/emcc_hello_world.fromasm b/test/emcc_hello_world.fromasm
index 17fb1483f..849b42aac 100644
--- a/test/emcc_hello_world.fromasm
+++ b/test/emcc_hello_world.fromasm
@@ -13329,12 +13329,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $7)
-         )
+         (get_local $7)
         )
        )
        (get_local $11)
diff --git a/test/emcc_hello_world.fromasm.clamp b/test/emcc_hello_world.fromasm.clamp
index 230b06413..1a55405ac 100644
--- a/test/emcc_hello_world.fromasm.clamp
+++ b/test/emcc_hello_world.fromasm.clamp
@@ -13379,12 +13379,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $7)
-         )
+         (get_local $7)
         )
        )
        (get_local $11)
diff --git a/test/emcc_hello_world.fromasm.imprecise b/test/emcc_hello_world.fromasm.imprecise
index d932b35eb..34f3e1c95 100644
--- a/test/emcc_hello_world.fromasm.imprecise
+++ b/test/emcc_hello_world.fromasm.imprecise
@@ -13263,14 +13263,11 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (tee_local $8
-           (i32.load
-            (get_local $1)
-           )
+         (tee_local $8
+          (i32.load
+           (get_local $1)
           )
          )
         )
diff --git a/test/memorygrowth.fromasm b/test/memorygrowth.fromasm
index c807bf937..291cd515d 100644
--- a/test/memorygrowth.fromasm
+++ b/test/memorygrowth.fromasm
@@ -6017,12 +6017,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $10)
-         )
+         (get_local $10)
         )
        )
        (get_local $14)
diff --git a/test/memorygrowth.fromasm.clamp b/test/memorygrowth.fromasm.clamp
index c807bf937..291cd515d 100644
--- a/test/memorygrowth.fromasm.clamp
+++ b/test/memorygrowth.fromasm.clamp
@@ -6017,12 +6017,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $10)
-         )
+         (get_local $10)
         )
        )
        (get_local $14)
diff --git a/test/memorygrowth.fromasm.imprecise b/test/memorygrowth.fromasm.imprecise
index bf23a9a1f..bb9d95844 100644
--- a/test/memorygrowth.fromasm.imprecise
+++ b/test/memorygrowth.fromasm.imprecise
@@ -6015,12 +6015,9 @@
      (if
       (i32.lt_u
        (tee_local $1
-        (i32.add
+        (i32.sub
          (get_local $1)
-         (i32.sub
-          (i32.const 0)
-          (get_local $10)
-         )
+         (get_local $10)
         )
        )
        (get_local $14)
diff --git a/test/passes/optimize-instructions.txt b/test/passes/optimize-instructions.txt
index 50858c81d..88709e2fe 100644
--- a/test/passes/optimize-instructions.txt
+++ b/test/passes/optimize-instructions.txt
@@ -2264,6 +2264,38 @@
    )
   )
  )
+ (func $subzero1 (; 56 ;) (type $3) (param $0 i32) (result i32)
+  (i32.sub
+   (i32.const 32)
+   (i32.clz
+    (get_local $0)
+   )
+  )
+ )
+ (func $subzero2 (; 57 ;) (type $3) (param $0 i32) (result i32)
+  (i32.sub
+   (i32.const 32)
+   (i32.clz
+    (get_local $0)
+   )
+  )
+ )
+ (func $subzero3 (; 58 ;) (type $6) (param $0 i32) (param $1 i32) (result i32)
+  (i32.sub
+   (get_local $1)
+   (i32.clz
+    (get_local $0)
+   )
+  )
+ )
+ (func $subzero4 (; 59 ;) (type $6) (param $0 i32) (param $1 i32) (result i32)
+  (i32.sub
+   (get_local $0)
+   (i32.clz
+    (get_local $1)
+   )
+  )
+ )
 )
 (module
  (type $0 (func))
diff --git a/test/passes/optimize-instructions.wast b/test/passes/optimize-instructions.wast
index 34b805f3d..60bfc9b7d 100644
--- a/test/passes/optimize-instructions.wast
+++ b/test/passes/optimize-instructions.wast
@@ -2663,6 +2663,50 @@
       (i32.and (i32.wrap/i64 (i64.const 1)) (i32.eqz (get_local $y)))
     )
   )
+  (func $subzero1 (param $0 i32) (result i32)
+    (i32.add
+     (i32.sub
+      (i32.const 1)
+      (i32.clz
+       (get_local $0)
+      )
+     )
+     (i32.const 31)
+    )
+  )
+  (func $subzero2 (param $0 i32) (result i32)
+    (i32.add
+     (i32.const 31)
+     (i32.sub
+      (i32.const 1)
+      (i32.clz
+       (get_local $0)
+      )
+     )
+    )
+  )
+  (func $subzero3 (param $0 i32) (param $1 i32) (result i32)
+    (i32.add
+     (i32.sub
+      (i32.const 0)
+      (i32.clz
+       (get_local $0)
+      )
+     )
+     (get_local $1)
+    )
+  )
+  (func $subzero4 (param $0 i32) (param $1 i32) (result i32)
+    (i32.add
+     (get_local $0)
+     (i32.sub
+      (i32.const 0)
+      (i32.clz
+       (get_local $1)
+      )
+     )
+    )
+  )
 )
 (module
   (import "env" "memory" (memory $0 (shared 256 256)))
@@ -2680,3 +2724,4 @@
    )
   )
 )
+