JIT: don't include a final return statement if we're sure the functio…

…n already returned
mayhemheroes · Jan 24, 2023 · 344422a · 344422a
1 parent 401101b
commit 344422a
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Showing 2 changed files with 22 additions and 11 deletions.
diff --git a/src/jsjit.c b/src/jsjit.c
@@ -828,11 +828,16 @@ void jsjExpression() {
   }
 }
 
-void jsjBlockNoBrackets() {
+// Returns true if isFunctionRoot and we had a RETURN statement (so we definitely already returned;
+bool jsjBlockNoBrackets() {
+  // if isFunctionRoot we're at the root scope
+  bool hadReturn = false;
   while (lex->tk && lex->tk!='}' && JSJ_PARSING) {
+    if (lex->tk == LEX_R_RETURN)
+      hadReturn = true;
     jsjStatement();
   }
-  return;
+  return hadReturn;
 }
 
 void jsjBlock() {
@@ -1061,12 +1066,14 @@ JsVar *jsjParseFunction() {
   if (JSJ_PARSING) { // if no error, re-parse and create code
     jslSeekTo(codeStartPosition);
     jit.phase = JSJP_EMIT; DEBUG_JIT("; ============ EMIT PHASE\n");
-    jsjBlockNoBrackets();
-    // optimisation: if the last statement was a return, no need for this. Could check if last instruction was 'POP {r4,r5,r6,r7,pc}'
-    // Return 'undefined' from function if no other return statement
-    DEBUG_JIT_EMIT("; END of function - return undefined\n");
-    jsjcLiteral32(0, 0);
-    jsjFunctionReturn(false/*isReturnStatement*/);
+    bool hadReturnStatement = jsjBlockNoBrackets(true);
+    // if this block had a return in it (eg not behind 'if'/etc), hadReturnStatement=true
+    // if so, we can skip adding a return statement
+    if (!hadReturnStatement) {
+      DEBUG_JIT_EMIT("; END of function - return undefined\n");
+      jsjcLiteral32(0, 0);
+      jsjFunctionReturn(false/*isReturnStatement*/);
+    }
   }
   JsVar *v = jsjcStop();
   JsVar *exception = jspGetException();

diff --git a/src/jsjitc.c b/src/jsjitc.c
@@ -50,8 +50,12 @@ const char *jsjcGetTypeName(JsjValueType t) {
 
 void jsjcDebugPrintf(const char *fmt, ...) {
   if (jsFlags & JSF_JIT_DEBUG) {
-    if (!jit.blockCount) jsiConsolePrintf("%6x: ", jsjcGetByteCount());
-    else jsiConsolePrintf("       : ");
+    if (fmt[0]==';') { // just a comment - don't add address
+      jsiConsolePrintf("      ");
+    } else {
+      if (!jit.blockCount) jsiConsolePrintf("%6x: ", jsjcGetByteCount());
+      else jsiConsolePrintf("       : ");
+    }
     va_list argp;
     va_start(argp, fmt);
     vcbprintf((vcbprintf_callback)jsiConsolePrint,0, fmt, argp);
@@ -71,7 +75,7 @@ void jsjcStart() {
 }
 
 JsVar *jsjcStop() {
-  jsjcDebugPrintf("VARS: %j\n", jit.vars);
+  jsjcDebugPrintf("; VARS: %j\n", jit.vars);
   jsvUnLock(jit.vars);
   jit.vars = 0;
   assert(jit.stackDepth == 0);