Avoid creating temporary objects in `read_irep_record_1`; close #4920

The basic idea of this change is from @dearblue.

Note: the arguments of `mrb_str_pool()` have changed, but the function
is provided for internal use (No `MRB_API`). So basically you don't have
to worry about the change.

2 files changed, 18 insertions, 21 deletions

diff --git a/src/load.c b/src/load.c
index 471ff3841..4184c4753 100644
--- a/src/load.c
+++ b/src/load.c
@@ -43,21 +43,25 @@ offset_crc_body(void)
 
 #ifndef MRB_WITHOUT_FLOAT
 static double
-str_to_double(mrb_state *mrb, mrb_value str)
+str_to_double(mrb_state *mrb, const char *p, size_t len)
 {
-  const char *p = RSTRING_PTR(str);
-  mrb_int len = RSTRING_LEN(str);
+  char buf[64];
 
   /* `i`, `inf`, `infinity` */
   if (len > 0 && p[0] == 'i') return INFINITY;
 
   /* `I`, `-inf`, `-infinity` */
   if (p[0] == 'I' || (len > 1 && p[0] == '-' && p[1] == 'i')) return -INFINITY;
+  mrb_assert(len < sizeof(buf));
+  strncpy(buf, p, len);
+  buf[len] = '\0';
 
-  return mrb_str_to_dbl(mrb, str, TRUE);
+  return mrb_cstr_to_dbl(mrb, buf, TRUE);
 }
 #endif
 
+mrb_value mrb_str_len_to_inum(mrb_state *mrb, const char *str, mrb_int len, mrb_int base, int badcheck);
+
 static mrb_irep*
 read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flags)
 {
@@ -119,21 +123,17 @@ read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flag
     irep->pool = (mrb_value*)mrb_malloc(mrb, sizeof(mrb_value) * plen);
 
     for (i = 0; i < plen; i++) {
-      mrb_value s;
+      const char *s;
+      mrb_bool st = (flags & FLAG_SRC_MALLOC)==0;
 
       tt = *src++; /* pool TT */
       pool_data_len = bin_to_uint16(src); /* pool data length */
       src += sizeof(uint16_t);
-      if (flags & FLAG_SRC_MALLOC) {
-        s = mrb_str_new(mrb, (char *)src, pool_data_len);
-      }
-      else {
-        s = mrb_str_new_static(mrb, (char *)src, pool_data_len);
-      }
+      s = (const char*)src;
       src += pool_data_len;
       switch (tt) { /* pool data */
       case IREP_TT_FIXNUM: {
-        mrb_value num = mrb_str_to_inum(mrb, s, 10, FALSE);
+        mrb_value num = mrb_str_len_to_inum(mrb, s, pool_data_len, 10, FALSE);
 #ifdef MRB_WITHOUT_FLOAT
         irep->pool[i] = num;
 #else
@@ -144,12 +144,12 @@ read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flag
 
 #ifndef MRB_WITHOUT_FLOAT
       case IREP_TT_FLOAT:
-        irep->pool[i] = mrb_float_pool(mrb, str_to_double(mrb, s));
+        irep->pool[i] = mrb_float_pool(mrb, str_to_double(mrb, s, pool_data_len));
         break;
 #endif
 
       case IREP_TT_STRING:
-        irep->pool[i] = mrb_str_pool(mrb, s);
+        irep->pool[i] = mrb_str_pool(mrb, s, pool_data_len, st);
         break;
 
       default:
diff --git a/src/string.c b/src/string.c
index 8141019b6..08c14d8e8 100644
--- a/src/string.c
+++ b/src/string.c
@@ -576,12 +576,9 @@ str_share(mrb_state *mrb, struct RString *orig, struct RString *s)
 }
 
 mrb_value
-mrb_str_pool(mrb_state *mrb, mrb_value str)
+mrb_str_pool(mrb_state *mrb, const char *p, mrb_int len, mrb_bool nofree)
 {
   struct RString *s = (struct RString *)mrb_malloc(mrb, sizeof(struct RString));
-  struct RString *orig = mrb_str_ptr(str);
-  const char *p = RSTR_PTR(orig);
-  size_t len = (size_t)RSTR_LEN(orig);
 
   s->tt = MRB_TT_STRING;
   s->c = mrb->string_class;
@@ -590,7 +587,7 @@ mrb_str_pool(mrb_state *mrb, mrb_value str)
   if (RSTR_EMBEDDABLE_P(len)) {
     str_init_embed(s, p, len);
   }
-  else if (RSTR_NOFREE_P(orig)) {
+  else if (nofree) {
     str_init_nofree(s, p, len);
   }
   else {
@@ -2242,7 +2239,7 @@ mrb_str_split_m(mrb_state *mrb, mrb_value str)
   return result;
 }
 
-static mrb_value
+mrb_value
 mrb_str_len_to_inum(mrb_state *mrb, const char *str, mrb_int len, mrb_int base, int badcheck)
 {
   const char *p = str;
@@ -2492,7 +2489,7 @@ mrb_str_to_i(mrb_state *mrb, mrb_value self)
 
 #ifndef MRB_WITHOUT_FLOAT
 MRB_API double
-mrb_cstr_to_dbl(mrb_state *mrb, const char * s, mrb_bool badcheck)
+mrb_cstr_to_dbl(mrb_state *mrb, const char *s, mrb_bool badcheck)
 {
   const char *p = s;
   char *end;