[codegen] Elide final return stmt if no value

This is a random driveby improvement. I realized that we can eliminate `return` statements if a) they have no value and b) they are in the top-level block. Functions implicitly return at that point — there can't be any succeeding instructions anyway — so we can save bytes in the output.
2025-11-01 09:12:30 +00:00 · 2022-11-22 08:03:40 -08:00
parent 1976fd03b4
commit 6bf5a1b396
35 changed files with 46 additions and 137 deletions
@@ -94,9 +94,11 @@ class CodegenVisitor
      t.SwitchCase
    >
 {
+  depth: number = 0;
  temp: Map<IdentifierId, t.Expression> = new Map();

  enterBlock(): t.Statement[] {
+    this.depth++;
    return [];
  }
  visitValue(
@@ -190,6 +192,11 @@ class CodegenVisitor
      case "return": {
        if (terminal.value !== null) {
          return t.returnStatement(terminal.value);
+        } else if (this.depth === 1) {
+          // A return at the top-level of a function must be the last instruction,
+          // and functions implicitly return after the last instruction of the top-level.
+          // Elide the return.
+          return t.emptyStatement();
        } else {
          return t.returnStatement();
        }
@@ -223,6 +230,7 @@ class CodegenVisitor
    }
  }
  leaveBlock(block: t.Statement[]): t.Statement {
+    this.depth--;
    return t.blockStatement(block);
  }
 }
@@ -140,9 +140,7 @@ flowchart TB
 ## Code

 ```javascript
-function mutate$0(x$1, y$2) {
-  return;
-}
+function mutate$0(x$1, y$2) {}

 ```
      
@@ -60,7 +60,6 @@ function f$0() {
  x$1 = x$1 + 1;
  x$1 = x$1 + 1;
  x$1 = x$1 >>> 1;
-  return;
 }

 ```
@@ -100,7 +99,6 @@ flowchart TB
 function g$0(a$1) {
  a$1.c.b = a$1.b.c + 1;
  a$1.c.b = a$1.b.c * 2;
-  return;
 }

 ```
@@ -38,9 +38,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -83,7 +83,6 @@ function foo$0(a$1, b$2, c$3) {
      bb7: if (c$3) break;
    }
  }
-  return;
 }

 ```
@@ -260,9 +260,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
 ## HIR
@@ -288,9 +286,7 @@ flowchart TB
 ## Code

 ```javascript
-function mayMutate$0() {
-  return;
-}
+function mayMutate$0() {}

 ```
      
@@ -38,9 +38,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
 ## HIR
@@ -52,7 +52,6 @@ function Component$0() {
  const b$2 = a$1;
  useFreeze$3(a$1);
  foo$4(b$2);
-  return;
 }

 ```
@@ -79,9 +78,7 @@ flowchart TB
 ## Code

 ```javascript
-function useFreeze$0() {
-  return;
-}
+function useFreeze$0() {}

 ```
 ## HIR
@@ -107,9 +104,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0(x$1) {
-  return;
-}
+function foo$0(x$1) {}

 ```
      
@@ -42,9 +42,7 @@ flowchart TB
 ## Code

 ```javascript
-function useFreeze$0() {
-  return;
-}
+function useFreeze$0() {}

 ```
 ## HIR
@@ -70,9 +68,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -80,9 +80,7 @@ flowchart TB
 ## Code

 ```javascript
-function useFreeze$0(x$1) {
-  return;
-}
+function useFreeze$0(x$1) {}

 ```
 ## HIR
@@ -108,9 +106,7 @@ flowchart TB
 ## Code

 ```javascript
-function call$0(x$1) {
-  return;
-}
+function call$0(x$1) {}

 ```
      
@@ -132,9 +132,7 @@ flowchart TB
 ## Code

 ```javascript
-function useFreeze$0(x$1) {
-  return;
-}
+function useFreeze$0(x$1) {}

 ```
 ## HIR
@@ -160,9 +158,7 @@ flowchart TB
 ## Code

 ```javascript
-function call$0(x$1) {
-  return;
-}
+function call$0(x$1) {}

 ```
      
@@ -56,9 +56,7 @@ flowchart TB
 ## Code

 ```javascript
-function compute$0() {
-  return;
-}
+function compute$0() {}

 ```
 ## HIR
@@ -84,9 +82,7 @@ flowchart TB
 ## Code

 ```javascript
-function mutate$0() {
-  return;
-}
+function mutate$0() {}

 ```
 ## HIR
@@ -112,9 +108,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -140,9 +134,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
 ## HIR
@@ -85,9 +85,7 @@ flowchart TB
 ## Code

 ```javascript
-function compute$0() {
-  return;
-}
+function compute$0() {}

 ```
 ## HIR
@@ -113,9 +111,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -141,9 +137,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
      
@@ -50,9 +50,7 @@ flowchart TB
 ## Code

 ```javascript
-function compute$0() {
-  return;
-}
+function compute$0() {}

 ```
 ## HIR
@@ -78,9 +76,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -106,9 +102,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
 ## HIR
@@ -88,9 +88,7 @@ flowchart TB
 ## Code

 ```javascript
-function compute$0() {
-  return;
-}
+function compute$0() {}

 ```
 ## HIR
@@ -116,9 +114,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -144,9 +140,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
      
@@ -75,8 +75,6 @@ function foo$0(a$1, b$2, c$3) {
      y$4.push(c$3);
    }
  }
-
-  return;
 }

 ```
@@ -244,9 +244,7 @@ flowchart TB
 ## Code

 ```javascript
-function f$0() {
-  return;
-}
+function f$0() {}

 ```
 ## HIR
@@ -272,9 +270,7 @@ flowchart TB
 ## Code

 ```javascript
-function g$0() {
-  return;
-}
+function g$0() {}

 ```
      
@@ -62,9 +62,7 @@ flowchart TB
 ## Code

 ```javascript
-function mutate$0(x$1, y$2) {
-  return;
-}
+function mutate$0(x$1, y$2) {}

 ```
 ## HIR
@@ -90,9 +88,7 @@ flowchart TB
 ## Code

 ```javascript
-function cond$0(x$1) {
-  return;
-}
+function cond$0(x$1) {}

 ```
 ## HIR
@@ -247,7 +243,6 @@ function Component$0(props$1) {
  }

  mutate$7(d$5, null);
-  return;
 }

 ```
@@ -58,9 +58,7 @@ flowchart TB
 ## Code

 ```javascript
-function mutate$0(x$1, y$2) {
-  return;
-}
+function mutate$0(x$1, y$2) {}

 ```
 ## HIR
@@ -174,7 +172,6 @@ function Component$0(props$1) {
  }

  mutate$8(x$6, null);
-  return;
 }

 ```
@@ -57,9 +57,7 @@ flowchart TB
 ## Code

 ```javascript
-function mutate$0() {
-  return;
-}
+function mutate$0() {}

 ```
 ## HIR
@@ -85,9 +83,7 @@ flowchart TB
 ## Code

 ```javascript
-function cond$0() {
-  return;
-}
+function cond$0() {}

 ```
 ## HIR
@@ -227,7 +223,6 @@ function Component$0(props$1) {
  }

  mutate$6(d$5, null);
-  return;
 }

 ```
@@ -189,7 +189,6 @@ function Component$0(props$1) {
  }

  x$2;
-  return;
 }

 ```
@@ -39,9 +39,7 @@ flowchart TB
 ## Code

 ```javascript
-function mutate$0() {
-  return;
-}
+function mutate$0() {}

 ```
 ## HIR
@@ -41,9 +41,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -38,9 +38,7 @@ flowchart TB
 ## Code

 ```javascript
-function foo$0() {
-  return;
-}
+function foo$0() {}

 ```
 ## HIR
@@ -110,7 +110,6 @@ function foo$0() {
  }

  y$2 = x$1;
-  return;
 }

 ```
@@ -78,7 +78,6 @@ function foo$0() {
  }

  y$2 = x$1;
-  return;
 }

 ```
@@ -83,8 +83,6 @@ function foo$0() {
  } else {
    let z$4 = x$1;
  }
-
-  return;
 }

 ```
@@ -36,9 +36,7 @@ flowchart TB
 ## Code

 ```javascript
-function Foo$0() {
-  return;
-}
+function Foo$0() {}

 ```
 ## HIR
@@ -40,9 +40,7 @@ flowchart TB
 ## Code

 ```javascript
-function log$0() {
-  return;
-}
+function log$0() {}

 ```
 ## HIR
@@ -119,7 +117,6 @@ function Foo$0(cond$1) {
  }

  log$4(str$2);
-  return;
 }

 ```
@@ -91,7 +91,6 @@ function foo$0() {
  }

  let x$4 = y$1;
-  return;
 }

 ```
@@ -41,7 +41,6 @@ flowchart TB
 function foo$0() {
  let x$1 = 1;
  let y$2 = 2;
-  return;
 }

 ```
@@ -67,8 +67,6 @@ function foo$0() {
  bb1: if (y$2) {
    let z$3 = x$1 + y$2;
  }
-
-  return;
 }

 ```
@@ -134,7 +134,6 @@ function foo$0() {
  }

  let y$9 = x$1;
-  return;
 }

 ```
@@ -191,8 +191,6 @@ function foo$0(x$1) {
      y$2 = 0;
    }
  }
-
-  return;
 }

 ```
@@ -94,7 +94,6 @@ function foo$0(a$1, b$2, c$3, d$4) {
  }

  d$4();
-  return;
 }

 ```