Refactor Perl_av_fetch, optimize path for non-negative key access

Author: bbrtj

av.c

@@ -266,9 +266,6 @@ S_adjust_index(pTHX_ AV *av, const MAGIC *mg, SSize_t *keyp)
 SV**
 Perl_av_fetch(pTHX_ AV *av, SSize_t key, I32 lval)
 {
-    SSize_t neg;
-    SSize_t size;
-
     PERL_ARGS_ASSERT_AV_FETCH;
 
     if (UNLIKELY(SvRMAGICAL(av))) {
@@ -291,24 +288,25 @@ Perl_av_fetch(pTHX_ AV *av, SSize_t key, I32 lval)
         }
     }
 
-    neg  = (key < 0);
-    size = AvFILLp(av) + 1;
-    key += neg * size; /* handle negative index without using branch */
+    SSize_t size = AvFILLp(av) + 1;
 
     /* the cast from SSize_t to Size_t allows both (key < 0) and (key >= size)
      * to be tested as a single condition */
     if ((Size_t)key >= (Size_t)size) {
-        if (UNLIKELY(neg))
+        if (LIKELY(key < 0))
+            key += size;
+        else
+            goto emptiness;
+
+        if (UNLIKELY(key < 0))
             return NULL;
-        goto emptiness;
     }
 
-    if (!AvARRAY(av)[key]) {
-      emptiness:
-        return lval ? av_store(av,key,newSV_type(SVt_NULL)) : NULL;
-    }
+    if (AvARRAY(av)[key])
+        return &AvARRAY(av)[key];
 
-    return &AvARRAY(av)[key];
+  emptiness:
+    return lval ? av_store(av,key,newSV_type(SVt_NULL)) : NULL;
 }
 
 /*