Improve string concatenation hack

- add more cases of in place string concatenation
  this temporary hack improves the microbench timing by 30% but
  has little impact on the test262 timings.

Makefile

@@ -48,9 +48,10 @@ PREFIX?=/usr/local
 #CONFIG_ASAN=y
 # use memory sanitizer
 #CONFIG_MSAN=y
-# include the code for BigFloat/BigDecimal, math mode and faster large integers
 # use UB sanitizer
 #CONFIG_UBSAN=y
+
+# include the code for BigFloat/BigDecimal and math mode
 CONFIG_BIGNUM=y
 
 OBJDIR=.obj

VERSION

@@ -1 +1 @@
-2024-01-13
+2024-02-14

quickjs.c

@@ -1454,6 +1454,10 @@ static inline int is_digit(int c) {
     return c >= '0' && c <= '9';
 }
 
+static inline int string_get(const JSString *p, int idx) {
+    return p->is_wide_char ? p->u.str16[idx] : p->u.str8[idx];
+}
+
 typedef struct JSClassShortDef {
     JSAtom class_name;
     JSClassFinalizer *finalizer;
@@ -2427,10 +2431,7 @@ static inline BOOL is_num_string(uint32_t *pval, const JSString *p)
     len = p->len;
     if (len == 0 || len > 10)
         return FALSE;
-    if (p->is_wide_char)
+    c = string_get(p, 0);
-        c = p->u.str16[0];
-    else
-        c = p->u.str8[0];
     if (is_num(c)) {
         if (c == '0') {
             if (len != 1)
@@ -2439,10 +2440,7 @@ static inline BOOL is_num_string(uint32_t *pval, const JSString *p)
         } else {
             n = c - '0';
             for(i = 1; i < len; i++) {
-                if (p->is_wide_char)
+                c = string_get(p, i);
-                    c = p->u.str16[i];
-                else
-                    c = p->u.str8[i];
                 if (!is_num(c))
                     return FALSE;
                 n64 = (uint64_t)n * 10 + (c - '0');
@@ -2487,10 +2485,24 @@ static uint32_t hash_string(const JSString *str, uint32_t h)
     return h;
 }
 
-static __maybe_unused void JS_DumpString(JSRuntime *rt,
+static __maybe_unused void JS_DumpChar(JSRuntime *rt, int c, int sep)
-                                                  const JSString *p)
 {
-    int i, c, sep;
+    if (c == sep || c == '\\') {
+        putchar('\\');
+        putchar(c);
+    } else if (c >= ' ' && c <= 126) {
+        putchar(c);
+    } else if (c == '\n') {
+        putchar('\\');
+        putchar('n');
+    } else {
+        printf("\\u%04x", c);
+    }
+}
+
+static __maybe_unused void JS_DumpString(JSRuntime *rt, const JSString *p)
+{
+    int i, sep;
 
     if (p == NULL) {
         printf("<null>");
@@ -2500,21 +2512,7 @@ static __maybe_unused void JS_DumpString(JSRuntime *rt,
     sep = (p->header.ref_count == 1) ? '\"' : '\'';
     putchar(sep);
     for(i = 0; i < p->len; i++) {
-        if (p->is_wide_char)
+        JS_DumpChar(rt, string_get(p, i), sep);
-            c = p->u.str16[i];
-        else
-            c = p->u.str8[i];
-        if (c == sep || c == '\\') {
-            putchar('\\');
-            putchar(c);
-        } else if (c >= ' ' && c <= 126) {
-            putchar(c);
-        } else if (c == '\n') {
-            putchar('\\');
-            putchar('n');
-        } else {
-            printf("\\u%04x", c);
-        }
     }
     putchar(sep);
 }
@@ -2857,6 +2855,7 @@ static JSAtom __JS_NewAtomInit(JSRuntime *rt, const char *str, int len,
     return __JS_NewAtom(rt, p, atom_type);
 }
 
+/* Warning: str must be ASCII only */
 static JSAtom __JS_FindAtom(JSRuntime *rt, const char *str, size_t len,
                             int atom_type)
 {
@@ -2951,11 +2950,13 @@ static JSAtom JS_NewAtomStr(JSContext *ctx, JSString *p)
     return __JS_NewAtom(rt, p, JS_ATOM_TYPE_STRING);
 }
 
+/* str is UTF-8 encoded */
 JSAtom JS_NewAtomLen(JSContext *ctx, const char *str, size_t len)
 {
     JSValue val;
 
     if (len == 0 || !is_digit(*str)) {
+        // XXX: this will not work if UTF-8 encoded str contains non ASCII bytes
         JSAtom atom = __JS_FindAtom(ctx->rt, str, len, JS_ATOM_TYPE_STRING);
         if (atom)
             return atom;
@@ -3061,10 +3062,7 @@ static const char *JS_AtomGetStrRT(JSRuntime *rt, char *buf, int buf_size,
                         return (const char *)str->u.str8;
                 }
                 for(i = 0; i < str->len; i++) {
-                    if (str->is_wide_char)
+                    c = string_get(str, i);
-                        c = str->u.str16[i];
-                    else
-                        c = str->u.str8[i];
                     if ((q - buf) >= buf_size - UTF8_CHAR_LEN_MAX)
                         break;
                     if (c < 128) {
@@ -3695,10 +3693,6 @@ static int string_buffer_putc(StringBuffer *s, uint32_t c)
     return string_buffer_putc16(s, c);
 }
 
-static int string_get(const JSString *p, int idx) {
-    return p->is_wide_char ? p->u.str16[idx] : p->u.str8[idx];
-}
-
 static int string_getc(const JSString *p, int *pidx)
 {
     int idx, c, c1;
@@ -4185,6 +4179,42 @@ static JSValue JS_ConcatString1(JSContext *ctx,
     return JS_MKPTR(JS_TAG_STRING, p);
 }
 
+static BOOL JS_ConcatStringInPlace(JSContext *ctx, JSString *p1, JSValueConst op2) {
+    if (JS_VALUE_GET_TAG(op2) == JS_TAG_STRING) {
+        JSString *p2 = JS_VALUE_GET_STRING(op2);
+        size_t size1;
+
+        if (p2->len == 0)
+            return TRUE;
+        if (p1->header.ref_count != 1)
+            return FALSE;
+        size1 = js_malloc_usable_size(ctx, p1);
+        if (p1->is_wide_char) {
+            if (size1 >= sizeof(*p1) + ((p1->len + p2->len) << 1)) {
+                if (p2->is_wide_char) {
+                    memcpy(p1->u.str16 + p1->len, p2->u.str16, p2->len << 1);
+                    p1->len += p2->len;
+                    return TRUE;
+                } else {
+                    size_t i;
+                    for (i = 0; i < p2->len; i++) {
+                        p1->u.str16[p1->len++] = p2->u.str8[i];
+                    }
+                    return TRUE;
+                }
+            }
+        } else if (!p2->is_wide_char) {
+            if (size1 >= sizeof(*p1) + p1->len + p2->len + 1) {
+                memcpy(p1->u.str8 + p1->len, p2->u.str8, p2->len);
+                p1->len += p2->len;
+                p1->u.str8[p1->len] = '\0';
+                return TRUE;
+            }
+        }
+    }
+    return FALSE;
+}
+
 /* op1 and op2 are converted to strings. For convenience, op1 or op2 =
    JS_EXCEPTION are accepted and return JS_EXCEPTION.  */
 static JSValue JS_ConcatString(JSContext *ctx, JSValue op1, JSValue op2)
@@ -4207,27 +4237,11 @@ static JSValue JS_ConcatString(JSContext *ctx, JSValue op1, JSValue op2)
         }
     }
     p1 = JS_VALUE_GET_STRING(op1);
-    p2 = JS_VALUE_GET_STRING(op2);
+    if (JS_ConcatStringInPlace(ctx, p1, op2)) {
-
-    /* XXX: could also check if p1 is empty */
-    if (p2->len == 0) {
-        goto ret_op1;
-    }
-    if (p1->header.ref_count == 1 && p1->is_wide_char == p2->is_wide_char
-    &&  js_malloc_usable_size(ctx, p1) >= sizeof(*p1) + ((p1->len + p2->len) << p2->is_wide_char) + 1 - p1->is_wide_char) {
-        /* Concatenate in place in available space at the end of p1 */
-        if (p1->is_wide_char) {
-            memcpy(p1->u.str16 + p1->len, p2->u.str16, p2->len << 1);
-            p1->len += p2->len;
-        } else {
-            memcpy(p1->u.str8 + p1->len, p2->u.str8, p2->len);
-            p1->len += p2->len;
-            p1->u.str8[p1->len] = '\0';
-        }
-    ret_op1:
         JS_FreeValue(ctx, op2);
         return op1;
     }
+    p2 = JS_VALUE_GET_STRING(op2);
     ret = JS_ConcatString1(ctx, p1, p2);
     JS_FreeValue(ctx, op1);
     JS_FreeValue(ctx, op2);
@@ -17778,6 +17792,11 @@ static JSValue JS_CallInternal(JSContext *caller_ctx, JSValueConst func_obj,
                     sp[-2] = __JS_NewFloat64(ctx, JS_VALUE_GET_FLOAT64(op1) +
                                              JS_VALUE_GET_FLOAT64(op2));
                     sp--;
+                } else if (JS_IsString(op1) && JS_IsString(op2)) {
+                    sp[-2] = JS_ConcatString(ctx, op1, op2);
+                    sp--;
+                    if (JS_IsException(sp[-1]))
+                        goto exception;
                 } else {
                 add_slow:
                     if (js_add_slow(ctx, sp))
@@ -17788,38 +17807,45 @@ static JSValue JS_CallInternal(JSContext *caller_ctx, JSValueConst func_obj,
             BREAK;
         CASE(OP_add_loc):
             {
+                JSValue op2;
                 JSValue *pv;
                 int idx;
                 idx = *pc;
                 pc += 1;
 
+                op2 = sp[-1];
                 pv = &var_buf[idx];
-                if (likely(JS_VALUE_IS_BOTH_INT(*pv, sp[-1]))) {
+                if (likely(JS_VALUE_IS_BOTH_INT(*pv, op2))) {
                     int64_t r;
-                    r = (int64_t)JS_VALUE_GET_INT(*pv) +
+                    r = (int64_t)JS_VALUE_GET_INT(*pv) + JS_VALUE_GET_INT(op2);
-                        JS_VALUE_GET_INT(sp[-1]);
                     if (unlikely((int)r != r))
                         goto add_loc_slow;
                     *pv = JS_NewInt32(ctx, r);
                     sp--;
-                } else if (JS_VALUE_GET_TAG(*pv) == JS_TAG_STRING) {
+                } else if (JS_VALUE_IS_BOTH_FLOAT(*pv, op2)) {
-                    JSValue op1;
+                    *pv = __JS_NewFloat64(ctx, JS_VALUE_GET_FLOAT64(*pv) +
-                    op1 = sp[-1];
+                                               JS_VALUE_GET_FLOAT64(op2));
                     sp--;
-                    op1 = JS_ToPrimitiveFree(ctx, op1, HINT_NONE);
+                } else if (JS_VALUE_GET_TAG(*pv) == JS_TAG_STRING) {
-                    if (JS_IsException(op1))
+                    sp--;
+                    op2 = JS_ToPrimitiveFree(ctx, op2, HINT_NONE);
+                    if (JS_IsException(op2))
                         goto exception;
-                    op1 = JS_ConcatString(ctx, JS_DupValue(ctx, *pv), op1);
+                    if (JS_ConcatStringInPlace(ctx, JS_VALUE_GET_STRING(*pv), op2)) {
-                    if (JS_IsException(op1))
+                        JS_FreeValue(ctx, op2);
-                        goto exception;
+                    } else {
-                    set_value(ctx, pv, op1);
+                        op2 = JS_ConcatString(ctx, JS_DupValue(ctx, *pv), op2);
+                        if (JS_IsException(op2))
+                            goto exception;
+                        set_value(ctx, pv, op2);
+                    }
                 } else {
                     JSValue ops[2];
                 add_loc_slow:
                     /* In case of exception, js_add_slow frees ops[0]
                        and ops[1], so we must duplicate *pv */
                     ops[0] = JS_DupValue(ctx, *pv);
-                    ops[1] = sp[-1];
+                    ops[1] = op2;
                     sp--;
                     if (js_add_slow(ctx, ops + 2))
                         goto exception;
@@ -35685,6 +35711,7 @@ static JSString *JS_ReadString(BCReaderState *s)
         js_free_string(s->ctx->rt, p);
         return NULL;
     }
+    // XXX: potential endianness issue
     memcpy(p->u.str8, s->ptr, size);
     s->ptr += size;
     if (!is_wide_char) {
@@ -41142,10 +41169,7 @@ static int js_string_get_own_property(JSContext *ctx,
             idx = __JS_AtomToUInt32(prop);
             if (idx < p1->len) {
                 if (desc) {
-                    if (p1->is_wide_char)
+                    ch = string_get(p1, idx);
-                        ch = p1->u.str16[idx];
-                    else
-                        ch = p1->u.str8[idx];
                     desc->flags = JS_PROP_ENUMERABLE;
                     desc->value = js_new_string_char(ctx, ch);
                     desc->getter = JS_UNDEFINED;
@@ -41411,10 +41435,7 @@ static JSValue js_string_charCodeAt(JSContext *ctx, JSValueConst this_val,
     if (idx < 0 || idx >= p->len) {
         ret = JS_NAN;
     } else {
-        if (p->is_wide_char)
+        c = string_get(p, idx);
-            c = p->u.str16[idx];
-        else
-            c = p->u.str8[idx];
         ret = JS_NewInt32(ctx, c);
     }
     JS_FreeValue(ctx, val);
@@ -41444,10 +41465,7 @@ static JSValue js_string_charAt(JSContext *ctx, JSValueConst this_val,
         else
             ret = js_new_string8(ctx, NULL, 0);
     } else {
-        if (p->is_wide_char)
+        c = string_get(p, idx);
-            c = p->u.str16[idx];
-        else
-            c = p->u.str8[idx];
         ret = js_new_string_char(ctx, c);
     }
     JS_FreeValue(ctx, val);
@@ -45324,7 +45342,7 @@ static int js_json_to_str(JSContext *ctx, JSONStringifyContext *jsc,
                     has_content = TRUE;
                 }
             }
-            if (has_content && JS_VALUE_GET_STRING(jsc->gap)->len != 0) {
+            if (has_content && !JS_IsEmptyString(jsc->gap)) {
                 string_buffer_putc8(jsc->b, '\n');
                 string_buffer_concat_value(jsc->b, indent);
             }