de-mathom Perl_sv_taint() part 3 (SvTAINT() branch remove)

"SvTAINT();" contains "if(PL_tainting && PL_tainted) sv_taint(sv);"
that is 2 One Byte reads and 2 branches. Collapse the 2 bool chars, to a
U16, so it is exactly 1 read, and 1 branch. Strips complexity from the
very bottom of the very hot newSVuv/newSViv/newSVuv, and other callers.
sv_taint(sv) has 62 callers, not sure how many do the 2 reads, 2 branches
SvTAINT(sv);, but the change decreased the size of miniperl.exe and
therefore perl541.dll, and branches were removed from the
newSVuv/newSViv/newSVuv trio.

Delta machine code bytes, between part 2 & 3 (this commit).

previous miniperl.exe Win64 .text section, VC 2022 -O1
0x1240AC bytes long

after
0x12408C bytes long

intrpvar.h

@@ -74,8 +74,9 @@ PERLVAR(I, multideref_pc, UNOP_AUX_item *)
 PERLVAR(I, curpm,	PMOP *)		/* what to do \ interps in REs from */
 PERLVAR(I, curpm_under,        PMOP *)                /* what to do \ interps in REs from */
 
-PERLVAR(I, tainting,	bool)		/* ? doing taint checks */
-PERLVARI(I, tainted,	bool, FALSE)	/* using variables controlled by $< */
+/* bool PL_tainting --- ? doing taint checks */
+/* bool PL_tainted  --- using variables controlled by $< */
+PERLVAR(I, taint,	TAINT_U)
 
 /* PL_delaymagic is currently used for two purposes: to assure simultaneous
  * updates in ($<,$>) = ..., and to assure atomic update in push/unshift

perl.c

@@ -249,6 +249,17 @@ perl_construct(pTHXx)
     SvREADONLY_on(&PL_sv_placeholder);
     SvREFCNT(&PL_sv_placeholder) = SvREFCNT_IMMORTAL;
 
+    STATIC_ASSERT_STMT(
+        sizeof(((TAINT_U *)0)->both)
+        == (sizeof(((TAINT_U *)0)->u.tainting) + sizeof(((TAINT_U *)0)->u.tainted))
+    );
+    STATIC_ASSERT_STMT(
+        sizeof(((TAINT_U *)0)->both)
+        == (STRUCT_OFFSET(TAINT_U, u.tainted) + sizeof(((TAINT_U *)0)->u.tainted))
+    );
+    STATIC_ASSERT_STMT(STRUCT_OFFSET(TAINT_U, both) == STRUCT_OFFSET(TAINT_U, u.tainting));
+    /* PL_taint.u.both = 0; */
+
     PL_sighandlerp  = Perl_sighandler;
     PL_sighandler1p = Perl_sighandler1;
     PL_sighandler3p = Perl_sighandler3;

perl.h

@@ -940,6 +940,8 @@ symbol would not be defined on C<L</EBCDIC>> platforms.
  * know what you're doing: tests and CPAN modules' tests are bound to fail.
  */
 #ifdef NO_TAINT_SUPPORT
+#   define PL_tainting		PL_taint.u.tainting
+#   define PL_tainted		PL_taint.u.tainted
 #   define TAINT		NOOP
 #   define TAINT_NOT		NOOP
 #   define TAINT_IF(c)		NOOP
@@ -948,6 +950,7 @@ symbol would not be defined on C<L</EBCDIC>> platforms.
 #   define TAINT_set(s)		NOOP
 #   define TAINT_get		0
 #   define TAINTING_get		0
+#   define TAINT_AND_TAINTING_get	0
 #   define TAINTING_set(s)	NOOP
 #   define TAINT_WARN_get       0
 #   define TAINT_WARN_set(s)    NOOP
@@ -1014,6 +1017,10 @@ violations are fatal.
 
 =cut
 */
+
+#define PL_tainting PL_taint.u.tainting
+#define PL_tainted PL_taint.u.tainted
+
     /* Set to tainted if we are running under tainting mode */
 #   define TAINT		(PL_tainted = PL_tainting)
 
@@ -1027,6 +1034,8 @@ violations are fatal.
 #   define TAINT_set(s)		(PL_tainted = cBOOL(s))
 #   define TAINT_get		(cBOOL(UNLIKELY(PL_tainted)))    /* Is something tainted? */
 #   define TAINTING_get		(cBOOL(UNLIKELY(PL_tainting)))
+/*  Efficient version of (PL_tainted && PL_tainting) */
+#   define TAINT_AND_TAINTING_get	(UNLIKELY(PL_taint.both == (TRUE | (TRUE << 8))))
 #   define TAINTING_set(s)	(PL_tainting = cBOOL(s))
 #   define TAINT_WARN_get       (PL_taint_warn)
 #   define TAINT_WARN_set(s)    (PL_taint_warn = cBOOL(s))
@@ -3309,6 +3318,14 @@ typedef struct padname PADNAME;
 #include "handy.h"
 #include "charclass_invlists.h"
 
+typedef union {
+    U16 both;
+    struct {
+        bool tainting;
+        bool tainted;
+    } u;
+} TAINT_U;
+
 #if defined(USE_LARGE_FILES) && !defined(NO_64_BIT_RAWIO)
 #   if LSEEKSIZE == 8 && !defined(USE_64_BIT_RAWIO)
 #       define USE_64_BIT_RAWIO	/* implicit */

sv.c

@@ -15912,7 +15912,7 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
 
 #ifndef NO_TAINT_SUPPORT
     /* Set tainting stuff before PerlIO_debug can possibly get called */
-    PL_tainting		= proto_perl->Itainting;
+    PL_tainting		= proto_perl->Itaint.u.tainting;
     PL_taint_warn	= proto_perl->Itaint_warn;
 #else
     PL_tainting         = FALSE;
@@ -16057,7 +16057,7 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
     PL_statcache	= proto_perl->Istatcache;
 
 #ifndef NO_TAINT_SUPPORT
-    PL_tainted		= proto_perl->Itainted;
+    PL_tainted		= proto_perl->Itaint.u.tainted;
 #else
     PL_tainted          = FALSE;
 #endif

sv.h

@@ -1735,8 +1735,8 @@ attention to precisely which outputs are influenced by which inputs.
 #define SvTAINT(sv)			\
     STMT_START {			\
         assert(TAINTING_get || !TAINT_get); \
-        if (UNLIKELY(TAINT_get))	\
-            SvTAINTED_on(sv);	        \
+        if (TAINT_AND_TAINTING_get) \
+            sv_taint(sv); \
     } STMT_END
 
 /*