When saving I32s, if the value is small enough save it with the type.

This uses a new type, SAVEt_I32_SMALL.

scope.c

@@ -426,10 +426,16 @@ void
 Perl_save_I32(pTHX_ I32 *intp)
 {
     dVAR;
+    const UV shifted = (UV)*intp << SAVE_TIGHT_SHIFT;
 
     PERL_ARGS_ASSERT_SAVE_I32;
 
-    save_pushi32ptr(*intp, intp, SAVEt_I32);
+    if ((I32)(shifted >> SAVE_TIGHT_SHIFT) == *intp) {
+	SSCHECK(2);
+	SSPUSHPTR(intp);
+	SSPUSHUV(SAVEt_I32_SMALL | shifted);
+    } else
+	save_pushi32ptr(*intp, intp, SAVEt_I32);
 }
 
 /* Cannot use save_sptr() to store a char* since the SV** cast will
@@ -804,6 +810,10 @@ Perl_leave_scope(pTHX_ I32 base)
 	    ptr = SSPOPPTR;
 	    *(bool*)ptr = cBOOL(uv >> 8);
 	    break;
+	case SAVEt_I32_SMALL:
+	    ptr = SSPOPPTR;
+	    *(I32*)ptr = (I32)(uv >> SAVE_TIGHT_SHIFT);
+	    break;
 	case SAVEt_I32:				/* I32 reference */
 	    ptr = SSPOPPTR;
 #ifdef PERL_DEBUG_READONLY_OPS

scope.h

@@ -55,6 +55,7 @@
 #define SAVEt_STACK_CXPOS	44
 #define SAVEt_PARSER		45
 #define SAVEt_ADELETE		46
+#define SAVEt_I32_SMALL		47
 
 #define SAVEf_SETMAGIC		1
 #define SAVEf_KEEPOLDELEM	2

sv.c

@@ -11583,6 +11583,7 @@ Perl_ss_dup(pTHX_ PerlInterpreter *proto_perl, CLONE_PARAMS* param)
 	    ptr = POPPTR(ss,ix);
 	    TOPPTR(nss,ix) = any_dup(ptr, proto_perl);
 	    /* Fall through */
+	case SAVEt_I32_SMALL:
 	case SAVEt_I16:				/* I16 reference */
 	case SAVEt_I8:				/* I8 reference */
 	case SAVEt_BOOL: