Only needed < 5.8

--- thrdvar.h~	Sat Jul 28 11:21:46 2001
+++ thrdvar.h	Sat Jul 28 11:33:34 2001
@@ -211,6 +211,8 @@
 PERLVARI(Treg_poscache, char *, Nullch)	/* cache of pos of WHILEM */
 PERLVAR(Treg_poscache_size, STRLEN)	/* size of pos cache of WHILEM */
 
+PERLVARI(Tpeepp,	peep_t, MEMBER_TO_FPTR(Perl_peep))
+					/* Pointer to peephole optimizer */
 PERLVARI(Tregcompp,	regcomp_t, MEMBER_TO_FPTR(Perl_pregcomp))
 					/* Pointer to REx compiler */
 PERLVARI(Tregexecp,	regexec_t, MEMBER_TO_FPTR(Perl_regexec_flags))
--- perl.c~	Sat Jul 28 11:22:18 2001
+++ perl.c	Sat Jul 28 11:24:03 2001
@@ -3804,6 +3804,7 @@
     (void) find_threadsv("@");	/* Ensure $@ is initialised early */
 
     PL_maxscream = -1;
+    PL_peepp = MEMBER_TO_FPTR(Perl_peep);
     PL_regcompp = MEMBER_TO_FPTR(Perl_pregcomp);
     PL_regexecp = MEMBER_TO_FPTR(Perl_regexec_flags);
     PL_regint_start = MEMBER_TO_FPTR(Perl_re_intuit_start);
--- perl.h~	Sat Jul 28 11:24:11 2001
+++ perl.h	Sat Jul 28 11:26:00 2001
@@ -2970,6 +2970,7 @@
 #define RsRECORD(sv)  (SvROK(sv) && (SvIV(SvRV(sv)) > 0))
 
 /* Enable variables which are pointers to functions */
+typedef void (CPERLscope(*peep_t))(pTHX_ OP* o);
 typedef regexp*(CPERLscope(*regcomp_t)) (pTHX_ char* exp, char* xend, PMOP* pm);
 typedef I32 (CPERLscope(*regexec_t)) (pTHX_ regexp* prog, char* stringarg,
 				      char* strend, char* strbeg, I32 minend,
--- sv.c~	Sat Jul 28 11:26:31 2001
+++ sv.c	Sat Jul 28 11:27:13 2001
@@ -10265,6 +10265,9 @@
     PL_reginterp_cnt	= 0;
     PL_reg_starttry	= 0;
 
+    /* Pluggable optimizer */
+    PL_peepp		= proto_perl->Tpeepp;
+
     if (!(flags & CLONEf_KEEP_PTR_TABLE)) {
         ptr_table_free(PL_ptr_table);
         PL_ptr_table = NULL;
--- util.c~	Sat Jul 28 11:27:22 2001
+++ util.c	Sat Jul 28 11:27:47 2001
@@ -3000,6 +3000,8 @@
     PL_reg_start_tmpl = 0;
     PL_reg_poscache = Nullch;
 
+    PL_peepp = MEMBER_TO_FPTR(Perl_peep);
+
     /* parent thread's data needs to be locked while we make copy */
     MUTEX_LOCK(&t->mutex);
 
--- op.c~	Sat Jul 28 11:27:56 2001
+++ op.c	Sat Jul 28 11:30:46 2001
@@ -20,6 +20,8 @@
 #include "perl.h"
 #include "keywords.h"
 
+#define CALL_PEEP(o) CALL_FPTR(PL_peepp)(o)
+
 /* #define PL_OP_SLAB_ALLOC */
 
 #ifdef PL_OP_SLAB_ALLOC
@@ -2174,7 +2176,7 @@
 	PL_eval_root->op_private |= OPpREFCOUNTED;
 	OpREFCNT_set(PL_eval_root, 1);
 	PL_eval_root->op_next = 0;
-	peep(PL_eval_start);
+	CALL_PEEP(PL_eval_start);
     }
     else {
 	if (!o)
@@ -2185,7 +2187,7 @@
 	PL_main_root->op_private |= OPpREFCOUNTED;
 	OpREFCNT_set(PL_main_root, 1);
 	PL_main_root->op_next = 0;
-	peep(PL_main_start);
+	CALL_PEEP(PL_main_start);
 	PL_compcv = 0;
 
 	/* Register with debugger */
@@ -2369,7 +2371,7 @@
 
     PL_op = curop = LINKLIST(o);
     o->op_next = 0;
-    peep(curop);
+    CALL_PEEP(curop);
     pp_pushmark();
     CALLRUNOPS(aTHX);
     PL_op = curop;
@@ -4809,7 +4811,7 @@
     OpREFCNT_set(CvROOT(cv), 1);
     CvSTART(cv) = LINKLIST(CvROOT(cv));
     CvROOT(cv)->op_next = 0;
-    peep(CvSTART(cv));
+    CALL_PEEP(CvSTART(cv));
 
     /* now that optimizer has done its work, adjust pad values */
     if (CvCLONE(cv)) {
@@ -5150,7 +5152,7 @@
     OpREFCNT_set(CvROOT(cv), 1);
     CvSTART(cv) = LINKLIST(CvROOT(cv));
     CvROOT(cv)->op_next = 0;
-    peep(CvSTART(cv));
+    CALL_PEEP(CvSTART(cv));
     op_free(o);
     PL_copline = NOLINE;
     LEAVE_SCOPE(floor);
@@ -6323,7 +6325,7 @@
 		    kid->op_next = 0;		/* just disconnect the leave */
 		k = kLISTOP->op_first;
 	    }
-	    peep(k);
+	    CALL_PEEP(k);
 
 	    kid = firstkid;
 	    if (o->op_type == OP_SORT) {
@@ -6853,7 +6855,7 @@
 	    o->op_seq = PL_op_seqmax++;
 	    while (cLOGOP->op_other->op_type == OP_NULL)
 		cLOGOP->op_other = cLOGOP->op_other->op_next;
-	    peep(cLOGOP->op_other);
+	    peep(cLOGOP->op_other); /* Recursive calls are not replaced by fptr calls */
 	    break;
 
 	case OP_ENTERLOOP: