simx86: eliminate exit_INHI for STI

Using TheCPU.eip for the block we can reliably check in DoExec
if the last executed block needs to inhibit ints, and as STI checks
signals immediately after it will trigger that check.

Similarly we can detect forever loops for the last block.

Flagging back refs in the node linker can then be limited to blocks
with F_FPOP (the original purpose of that flagging).

Author: bartoldeman

src/base/emu-i386/simx86/codegen-sim.c

@@ -3305,7 +3305,7 @@ static unsigned int _Sim_helper(unsigned int mem_ref, unsigned int data, int mod
 				    e_printf("Return for STI ASAP fl=%08x\n",
 					    EFLAGS);
 				/* force exit after next compiled block execution */
-				exit_pending_or(exit_RPIC|exit_INHI);
+				exit_pending_or(exit_RPIC);
 			    }
 			}
 			break;

src/base/emu-i386/simx86/codegen.c

@@ -589,16 +589,10 @@ static unsigned int Exec_pre(unsigned char *ecpu)
 	return flg;
 }
 
-static void Exec_post(unsigned long flg, unsigned int mem_ref,
-		      unsigned short seqflg)
+static void Exec_post(unsigned long flg, unsigned int mem_ref)
 {
 	EFLAGS = (EFLAGS & ~EFLAGS_CC) | (flg &	EFLAGS_CC);
 	TheCPU.mem_ref = mem_ref;
-	/* checking for infinite loops, flagged in JumpGen() */
-	if ((seqflg & F_SLFJ) && !(EFLAGS & (VIF|IF|TF))) {
-		error("!Forever loop!\n");
-		leavedos_main(0xebfe);
-	}
 }
 
 static void HandleEmuSignals(int tfset)
@@ -612,8 +606,7 @@ static void HandleEmuSignals(int tfset)
 #endif
 	if (tfset) {
 		/* force exit for single step trap */
-		if (!TheCPU.err)
-			TheCPU.err = EXCP01_SSTP;
+		TheCPU.err = EXCP01_SSTP;
 	}
 	//else if (CEmuStat & CeS_DRTRAP) {
 	//	if (e_debug_check(PC)) {
@@ -695,8 +688,6 @@ unsigned int DoExec(TNode *G, unsigned *pLastXKey)
 	hitimer_t TimeStartExec;
 	if (debug_level('e')) TimeStartExec = GETTSC();
 #endif
-	/* these flags need to be checked only once for the node */
-	G->flags &= ~(F_SPEC|F_LEAV);
 	/* if there is just one compiled instruction inhibition
 	   should be ignored unconditionally if signals and traps
 	   were already ignored, e.g. two "sti"s in a row */
@@ -706,22 +697,25 @@ unsigned int DoExec(TNode *G, unsigned *pLastXKey)
 	flg = Exec_pre(ecpu);
 #if !defined(ASM_DUMP) && !defined(SINGLESTEP)
 	/* try fast inner loop if nothing special is going on */
-	if (!tfset && !block_inhibit && !debug_level('e')) {
+	if (!tfset && !block_inhibit && !debug_level('e') &&
+	    !(seqflg & (F_SPEC|F_LEAV))) {
 		while (1) {
 			ePC = ExecOne(G, &mem_ref, &flg, ecpu, pLastXKey);
-			if (TheCPU.err || exit_pending() ||
-			    (seqflg & (F_INHI|F_SLFJ|F_SPEC|F_LEAV)))
+			if (TheCPU.err || exit_pending())
 				break;
 			G = FindTree(ePC);
 			if (!G || !GoodNode(G))
 				break;
-			seqflg = G->flags;
 		}
 	} else
 #endif
+	{
+		/* these flags need to be checked only once for the node */
+		G->flags &= ~(F_SPEC|F_LEAV);
 		ePC = ExecOne(G, &mem_ref, &flg, ecpu, pLastXKey);
+	}
 	// G is unreliable (maybe deleted) past this point!
-	Exec_post(flg, mem_ref, seqflg);
+	Exec_post(flg, mem_ref);
 
 	if (debug_level('e')) {
 #if PROFILE >= 2
@@ -745,14 +739,27 @@ unsigned int DoExec(TNode *G, unsigned *pLastXKey)
 	/* exit_pending at this point is non-zero if there was ANY signal,
 	 * not just a SIGALRM
 	 */
-	if (((seqflg & F_INHI) || (exit_pending() & exit_INHI)) && !block_inhibit) {
-		/* ignore signals and traps for movss/popss */
-		CEmuStat |= CeS_INHI;
-		if (exit_pending() & exit_INHI)
-			exit_pending_and(~exit_INHI);
-	} else {
-		CEmuStat &= ~CeS_INHI;
-		HandleEmuSignals(tfset);
+	CEmuStat &= ~CeS_INHI;
+	if (TheCPU.err) {
+		/* CPU exceptions override everything else */
+		exit_pending_w(0);
+	}
+	else if (exit_pending() || tfset) {
+		/* TheCPU.eip points to the first instruction of the last
+		   executed block, except for real-mode retf, which neither
+		   inhibits interrupts nor causes forever loops */
+		TNode *LastG = FindTree(LONG_CS + TheCPU.eip);
+		seqflg = LastG ? LastG->flags : 0;
+		if ((seqflg & F_INHI) && !block_inhibit)
+			/* ignore signals and traps for movss/popss */
+			CEmuStat |= CeS_INHI;
+		else
+			HandleEmuSignals(tfset);
+		/* checking for infinite loops, flagged in JumpGen() */
+		if ((seqflg & F_SLFJ) && !(EFLAGS & (VIF|IF|TF))) {
+			error("!Forever loop!\n");
+			leavedos_main(0xebfe);
+		}
 	}
 
 #if defined(SINGLESTEP)

src/base/emu-i386/simx86/emu86.h

@@ -683,9 +683,8 @@ extern int SpecPrejits;
 
 #define exit_SIGPEND	0x01	/* signal pending mask */
 #define exit_RPIC	0x02	/* pic asks for interruption */
-#define exit_STI	0x04	/* STI shadow active */
-#define exit_INHI	0x08	/* inhibit interrupts(pop ss; pop sp et sim.) */
-#define exit_TRAP	0x10	/* INT01 Sstep set by POPF/IRET */
+#define exit_STI	0x04	/* exit from IF set with VIP active in vm86 */
+#define exit_TRAP	0x08	/* INT01 Sstep set by POPF/IRET */
 
 /////////////////////////////////////////////////////////////////////////////
 

src/base/emu-i386/simx86/trees.c

@@ -750,8 +750,7 @@ static void linknode(TNode *LG, TNode *G, linkdesc *L, unsigned target_type)
 	backref *B;
 
 	// points to current node, which can't be a forever loop?
-	if (L->target!=G->key || !(LG->unlinked_jmp_targets & target_type) ||
-	    (G->flags & F_SLFJ))
+	if (L->target!=G->key || !(LG->unlinked_jmp_targets & target_type))
 		return;
 
 	if (L->ref!=0) {
@@ -787,7 +786,7 @@ static void linknode(TNode *LG, TNode *G, linkdesc *L, unsigned target_type)
 			 G,G->key,G->addr,
 			 L->target, B->branch, G->nrefs, L->ref, *L->ref);
 	}
-	_nodeflagbackrefs(LG, G->flags);
+	_nodeflagbackrefs(LG, G->flags&F_FPOP);
 	if (debug_level('e')>8) {
 		backref *bk = G->bkr.next;
 #ifdef DEBUG_LINKER