variable.h: add prefetch to bsearch_idx

matz · Gemini · matz · commit 670b54f85934 · 2025-07-11T10:09:35.000+09:00
This commit introduces memory prefetching to the `bsearch_idx` functions
in `src/class.c` and `src/variable.c` to improve performance.

A new macro `MRB_MEM_PREFETCH` is defined in `include/mruby/variable.h`
which uses `__builtin_prefetch` if available.

Co-authored-by: Gemini &lt;gemini@google.com&gt;
diff --git a/include/mruby/variable.h b/include/mruby/variable.h
@@ -7,6 +7,12 @@
 #ifndef MRUBY_VARIABLE_H
 #define MRUBY_VARIABLE_H
 
+#if defined(__GNUC__) || defined(__clang__)
+#define MRB_MEM_PREFETCH(addr) __builtin_prefetch(addr, 0, 1)
+#else
+#define MRB_MEM_PREFETCH(addr)
+#endif
+
 #include "common.h"
 
 /**
diff --git a/src/class.c b/src/class.c
@@ -105,6 +105,8 @@ bsearch_idx(mrb_sym *keys, int size, mrb_sym target)
   /* While more than one element remains, halve the range each iteration */
   while (n > 1) {
     int half = n >> 1;
+    MRB_MEM_PREFETCH(p + (half >> 1));
+    MRB_MEM_PREFETCH(p + half + (half >> 1));
     mrb_sym mid_sym = MT_KEY_SYM(p[half]);
     /*
      * Update pointer p without a branch:
diff --git a/src/variable.c b/src/variable.c
@@ -78,6 +78,8 @@ bsearch_idx(mrb_sym *keys, int size, mrb_sym target) {
   /* While more than one element remains, halve the range each iteration */
   while (n > 1) {
     int half = n >> 1;
+    MRB_MEM_PREFETCH(p + (half >> 1));
+    MRB_MEM_PREFETCH(p + half + (half >> 1));
     mrb_sym mid_sym = p[half];
     /*
      * Update pointer p without a branch:
