Notes on unary EQZ in compileBinary EQ

src/compiler.ts

@@ -1545,6 +1545,11 @@ export class Compiler extends DiagnosticEmitter {
 
       case Token.EQUALS_EQUALS:
       case Token.EQUALS_EQUALS_EQUALS:
+
+        // NOTE that this favors correctness, in terms of emitting a binary expression, over
+        // checking for a possible use of unary EQZ. while the most classic of all optimizations,
+        // that's not what the source told us to do. for reference, `!left` emits unary EQZ.
+
         left = this.compileExpression(expression.left, contextualType, ConversionKind.NONE);
         right = this.compileExpression(expression.right, this.currentType);
 

tests/compiler/fmod.optimized.wast

@@ -154,18 +154,18 @@
         )
        )
        (block
-        (set_local $4
-         (i64.shl
-          (get_local $4)
-          (i64.const 1)
-         )
-        )
         (set_local $3
          (i32.sub
           (get_local $3)
           (i32.const 1)
          )
         )
+        (set_local $4
+         (i64.shl
+          (get_local $4)
+          (i64.const 1)
+         )
+        )
         (br $continue|0)
        )
       )
@@ -211,18 +211,18 @@
         )
        )
        (block
-        (set_local $4
-         (i64.shl
-          (get_local $4)
-          (i64.const 1)
-         )
-        )
         (set_local $6
          (i32.sub
           (get_local $6)
           (i32.const 1)
          )
         )
+        (set_local $4
+         (i64.shl
+          (get_local $4)
+          (i64.const 1)
+         )
+        )
         (br $continue|1)
        )
       )
@@ -332,18 +332,18 @@
      )
     )
     (block
-     (set_local $2
-      (i64.shl
-       (get_local $2)
-       (i64.const 1)
-      )
-     )
      (set_local $3
       (i32.sub
        (get_local $3)
        (i32.const 1)
       )
      )
+     (set_local $2
+      (i64.shl
+       (get_local $2)
+       (i64.const 1)
+      )
+     )
      (br $continue|3)
     )
    )

tests/compiler/fmod.ts

@@ -15,14 +15,16 @@ export function fmod(x: f64, y: f64): f64 {
   }
 
   if (!ex) {
-    for (var i = ux << 12; !(i >> 63); ex--) i <<= 1;
+    for (var i = ux << 12; !(i >> 63); i <<= 1)
+      --ex;
     ux <<= -ex + 1;
   } else {
     ux &= -1 >> 12;
     ux |= 1 << 52;
   }
   if (!ey) {
-    for (i = uy << 12; !(i >> 63); ey--) i <<= 1;
+    for (i = uy << 12; !(i >> 63); i <<= 1)
+      --ey;
     uy <<= -ey + 1;
   } else {
     uy &= -1 >> 12;
@@ -44,7 +46,8 @@ export function fmod(x: f64, y: f64): f64 {
       return 0 * x;
     ux = i;
   }
-  for (; !(ux >> 52); ex--) ux <<= 1;
+  for (; !(ux >> 52); ux <<= 1)
+    --ex;
 
   if (ex > 0) {
     ux -= 1 << 52;

tests/compiler/fmod.wast

@@ -165,26 +165,18 @@
         )
        )
        (block
+        (set_local $4
+         (i32.sub
+          (get_local $4)
+          (i32.const 1)
+         )
+        )
         (set_local $9
          (i64.shl
           (get_local $9)
           (i64.const 1)
          )
         )
-        (drop
-         (block (result i32)
-          (set_local $8
-           (get_local $4)
-          )
-          (set_local $4
-           (i32.sub
-            (get_local $8)
-            (i32.const 1)
-           )
-          )
-          (get_local $8)
-         )
-        )
         (br $continue|0)
        )
       )
@@ -250,26 +242,18 @@
         )
        )
        (block
+        (set_local $5
+         (i32.sub
+          (get_local $5)
+          (i32.const 1)
+         )
+        )
         (set_local $9
          (i64.shl
           (get_local $9)
           (i64.const 1)
          )
         )
-        (drop
-         (block (result i32)
-          (set_local $8
-           (get_local $5)
-          )
-          (set_local $5
-           (i32.sub
-            (get_local $8)
-            (i32.const 1)
-           )
-          )
-          (get_local $8)
-         )
-        )
         (br $continue|1)
        )
       )
@@ -421,26 +405,18 @@
       )
      )
      (block
+      (set_local $4
+       (i32.sub
+        (get_local $4)
+        (i32.const 1)
+       )
+      )
       (set_local $2
        (i64.shl
         (get_local $2)
         (i64.const 1)
        )
       )
-      (drop
-       (block (result i32)
-        (set_local $8
-         (get_local $4)
-        )
-        (set_local $4
-         (i32.sub
-          (get_local $8)
-          (i32.const 1)
-         )
-        )
-        (get_local $8)
-       )
-      )
       (br $continue|3)
      )
     )