From b1b737ed6cac47b82f267a2c3e7d4a36d40a02cf Mon Sep 17 00:00:00 2001
From: George Koehler <xkernigh@netscape.net>
Date: Mon, 5 Mar 2018 13:32:06 -0500
Subject: [PATCH] Optimize procedures that do both a / b and a % b.

Enable this in CS for PowerPC; disable it for all other machines.
PowerPC has no remainder instruction; the back end uses division to
compute remainder.  If CS finds both a / b and a % b, then CS now
rewrites a % b as a - b * (a / b) and computes a / b only once.  This
removes an extra division in the PowerPC code, so it saves both time
and space.

I have not considered whether to enable this optimization for other
machines.  It might be less useful in machines with a remainder
instruction.  Also, if a % b occurs before a / b, the EM code gets a
DUP.  PowerPC ncg handles this DUP well; other back ends might not.
---
 util/ego/cs/cs.h             | 13 +++---
 util/ego/cs/cs_avail.c       |  5 +-
 util/ego/cs/cs_elim.c        | 90 ++++++++++++++++++++++++++++++------
 util/ego/cs/cs_partit.c      |  5 +-
 util/ego/cs/cs_profit.c      | 12 +++++
 util/ego/cs/cs_profit.h      |  5 ++
 util/ego/cs/cs_vnm.c         | 37 +++++++++++++++
 util/ego/descr/em22.descr    |  1 +
 util/ego/descr/em24.descr    |  1 +
 util/ego/descr/em44.descr    |  1 +
 util/ego/descr/i386.descr    |  1 +
 util/ego/descr/i86.descr     |  1 +
 util/ego/descr/m68020.descr  |  1 +
 util/ego/descr/m68k2.descr   |  1 +
 util/ego/descr/m68k4.descr   |  1 +
 util/ego/descr/pdp.descr     |  1 +
 util/ego/descr/powerpc.descr |  1 +
 util/ego/descr/sparc.descr   |  1 +
 util/ego/descr/vax4.descr    |  1 +
 19 files changed, 156 insertions(+), 23 deletions(-)

diff --git a/util/ego/cs/cs.h b/util/ego/cs/cs.h
index c749427a5..7a2ebde7b 100644
--- a/util/ego/cs/cs.h
+++ b/util/ego/cs/cs.h
@@ -88,12 +88,13 @@ struct occur {
 #define UNAIR_OP	6
 #define BINAIR_OP	7
 #define TERNAIR_OP	8
-#define KILL_ENTITY	9
-#define SIDE_EFFECTS	10
-#define FIDDLE_STACK	11
-#define IGNORE		12
-#define HOPELESS	13
-#define BBLOCK_END	14
+#define REMAINDER	9
+#define KILL_ENTITY	10
+#define SIDE_EFFECTS	11
+#define FIDDLE_STACK	12
+#define IGNORE		13
+#define HOPELESS	14
+#define BBLOCK_END	15
 
 struct avail {
 	avail_p	av_before;	/* Ptr to earlier discovered expressions. */
diff --git a/util/ego/cs/cs_avail.c b/util/ego/cs/cs_avail.c
index 025132a2e..b28cc496a 100644
--- a/util/ego/cs/cs_avail.c
+++ b/util/ego/cs/cs_avail.c
@@ -54,6 +54,7 @@ STATIC bool same_avail(byte kind, avail_p avp1, avail_p avp2)
 		case UNAIR_OP:
 			return	avp1->av_operand == avp2->av_operand;
 		case BINAIR_OP:
+		case REMAINDER:
 			if (commutative(avp1->av_instr & BMASK))
 				return	avp1->av_oleft == avp2->av_oleft &&
 					avp1->av_oright == avp2->av_oright
@@ -124,6 +125,7 @@ STATIC void copy_avail(int kind, avail_p src, avail_p dst)
 			dst->av_operand = src->av_operand;
 			break;
 		case BINAIR_OP:
+		case REMAINDER:
 			dst->av_oleft = src->av_oleft;
 			dst->av_oright = src->av_oright;
 			break;
@@ -160,7 +162,8 @@ avail_p av_enter(avail_p avp, occur_p ocp, int kind)
 	/* Remember local, if any, that holds result. */
 	if (avp->av_instr != (byte) INSTR(last)) {
 		/* Only possible when instr is the implicit AAR in 
-		 * a LAR or SAR.
+		 * a LAR or SAR, or the implicit DVI in an RMI, or
+		 * DVU in RMU.
 		 */
 		ravp->av_saveloc = (entity_p) 0;
 	} else {
diff --git a/util/ego/cs/cs_elim.c b/util/ego/cs/cs_elim.c
index 767517bd8..7dce0df09 100644
--- a/util/ego/cs/cs_elim.c
+++ b/util/ego/cs/cs_elim.c
@@ -101,12 +101,49 @@ STATIC void complete_aar(line_p lnp, int instr, valnum descr_vn)
 	dlink(lnp, lindir);
 }
 
+STATIC void complete_dv_as_rm(line_p lnp, avail_p avp, bool first)
+{
+	/* Complete a / b as a % b = a - b * (a / b). For the first
+	 * occurrence, lnp must stack q, where q = a / b. We prepend a
+	 * DUP to change postfix a b / into a b a b /, then append a
+	 * MLI/MLU and SBI/SBU to make a b a b / * -.
+	 *
+	 * For later occurences, lnp must stack a b q.  We append the
+	 * MLI/MLU and SBI/SBU.
+	 */
+	line_p dv, dup, ml, sb;
+	offset size;
+	bool s;
+
+	size = avp->av_size;
+	s = (avp->av_instr == (byte) op_dvi);
+	assert(s || avp->av_instr == (byte) op_dvu);
+	if (first) {
+		/* Prepend our DUP to avp->av_found, to get before the
+		 * DVI if lnp points to the LOL in DVI STL LOL.
+		 */
+		dup = int_line(2 * size);
+		dup->l_instr = op_dup;
+		dv = avp->av_found;
+		dlink(dv->l_prev, dup);
+		dlink(dup, dv);
+	}
+	ml = int_line(size);
+	sb = int_line(size);
+	ml->l_instr = (s ? op_mli : op_mlu);
+	sb->l_instr = (s ? op_sbi : op_sbu);
+	dlink(sb, lnp->l_next);
+	dlink(ml, sb);
+	dlink(lnp, ml);
+}
+
 STATIC void replace(occur_p ocp, offset tmp, avail_p avp)
 {
 	/* Replace the lines in the occurrence in ocp by a load of the
 	 * temporary with offset tmp.
 	 */
 	register line_p lol, first, last;
+	register int instr;
 
 	assert(avp->av_size == ws || avp->av_size == 2*ws);
 
@@ -119,13 +156,24 @@ STATIC void replace(occur_p ocp, offset tmp, avail_p avp)
 	if (first->l_prev == (line_p) 0) ocp->oc_belongs->b_start = lol;
 	dlink(first->l_prev, lol);
 
-	if (avp->av_instr == (byte) op_aar) {
-		/* There may actually be a LAR or a SAR instruction; in that
-		 * case we have to complete the array-instruction.
-		 */
-		register int instr = INSTR(last);
-
-		if (instr != op_aar) complete_aar(lol, instr, avp->av_othird);
+	instr = INSTR(last);
+	switch (avp->av_instr & 0377) {
+		case op_aar:
+			/* There may actually be a LAR or a SAR
+			 * instruction; in that case we have to
+			 * complete the array-instruction.
+			 */
+			if (instr != op_aar)
+				complete_aar(lol, instr, avp->av_othird);
+			break;
+		case op_dvi:
+			if (instr == op_rmi)
+				complete_dv_as_rm(lol, avp, FALSE);
+			break;
+		case op_dvu:
+			if (instr == op_rmu)
+				complete_dv_as_rm(lol, avp, FALSE);
+			break;
 	}
 
 	/* Throw away the by now useless lines. */
@@ -142,6 +190,7 @@ STATIC void append(avail_p avp, offset tmp)
 	 * within a lar or sar, we must first generate the aar.
 	 */
 	register line_p stl, lol;
+	register int instr;
 
 	assert(avp->av_size == ws || avp->av_size == 2*ws);
 
@@ -154,13 +203,26 @@ STATIC void append(avail_p avp, offset tmp)
 	dlink(stl, lol);
 	dlink(avp->av_found, stl);
 
-	if (avp->av_instr == (byte) op_aar) {
-		register int instr = INSTR(avp->av_found);
-
-		if (instr != op_aar) {
-			complete_aar(lol, instr, avp->av_othird);
-			avp->av_found->l_instr = op_aar;
-		}
+	instr = INSTR(avp->av_found);
+	switch (avp->av_instr & 0377) {
+		case op_aar:
+			if (instr != op_aar) {
+				complete_aar(lol, instr, avp->av_othird);
+				avp->av_found->l_instr = op_aar;
+			}
+			break;
+		case op_dvi:
+			if (instr == op_rmi) {
+				complete_dv_as_rm(lol, avp, TRUE);
+				avp->av_found->l_instr = op_dvi;
+			}
+			break;
+		case op_dvu:
+			if (instr == op_rmu) {
+				complete_dv_as_rm(lol, avp, TRUE);
+				avp->av_found->l_instr = op_dvu;
+			}
+			break;
 	}
 }
 
diff --git a/util/ego/cs/cs_partit.c b/util/ego/cs/cs_partit.c
index e6d3b1fdf..b020ebcfa 100644
--- a/util/ego/cs/cs_partit.c
+++ b/util/ego/cs/cs_partit.c
@@ -125,8 +125,8 @@ STATIC struct {
 /* nop */	HOPELESS,	XXX,	XXX,	XXX,	XXX,
 /* rck */	BBLOCK_END,	XXX,	XXX,	XXX,	XXX,
 /* ret */	BBLOCK_END,	XXX,	XXX,	XXX,	XXX,
-/* rmi */	BINAIR_OP,	ARGW,	ARGW,	ARGW,	ANY,
-/* rmu */	BINAIR_OP,	ARGW,	ARGW,	ARGW,	ANY,
+/* rmi */	REMAINDER,	ARGW,	ARGW,	ARGW,	ANY,
+/* rmu */	REMAINDER,	ARGW,	ARGW,	ARGW,	ANY,
 /* rol */	BINAIR_OP,	ARGW,	WS,	ARGW,	ANY,
 /* ror */	BINAIR_OP,	ARGW,	WS,	ARGW,	ANY,
 /* rtt */	BBLOCK_END,	XXX,	XXX,	XXX,	XXX,
@@ -203,6 +203,7 @@ bool stack_group(int instr)
 		case UNAIR_OP:
 		case BINAIR_OP:
 		case TERNAIR_OP:
+		case REMAINDER:
 			return TRUE;
 		default:
 			return FALSE;
diff --git a/util/ego/cs/cs_profit.c b/util/ego/cs/cs_profit.c
index 8845aaa29..a92028c36 100644
--- a/util/ego/cs/cs_profit.c
+++ b/util/ego/cs/cs_profit.c
@@ -25,6 +25,7 @@ STATIC cset	forbidden;
 STATIC cset	sli_counts;
 STATIC short	LX_threshold;
 STATIC short	AR_limit;
+STATIC bool	RM_to_DV;
 
 STATIC void get_instrs(FILE *f, cset *s_p)
 {
@@ -97,6 +98,12 @@ void cs_machinit(void *vp)
 	fscanf(f, "%d", &space);
 	AR_limit = space;
 
+	/* Read whether to convert a remainder RMI/RMU to a division
+	 * DVI/DVU using the formula a % b = a - b * (a / b).
+	 */
+	fscanf(f, "%d %d", &time, &space);
+	RM_to_DV = time_space_ratio >= 50 ? time : space;
+
 	/* Read for what counts we must not eliminate an SLI instruction
 	 * when it is part of an array-index computation.
 	 */
@@ -126,6 +133,11 @@ bool may_become_aar(avail_p avp)
 	return TRUE;
 }
 
+bool may_become_dv(void)
+{
+	return RM_to_DV;
+}
+
 STATIC bool sli_no_eliminate(line_p lnp)
 {
 	/* Return whether the SLI-instruction in lnp is part of
diff --git a/util/ego/cs/cs_profit.h b/util/ego/cs/cs_profit.h
index 43f2bade9..3d1972d24 100644
--- a/util/ego/cs/cs_profit.h
+++ b/util/ego/cs/cs_profit.h
@@ -13,6 +13,11 @@ bool may_become_aar(avail_p avp);
 				 * an AAR LOI/STI.
 				 */
 
+bool may_become_dv(void);	/*
+				 * Return whether an RMI/RMU may become
+				 * a DVI/DVU: a % b = a - (a / b * b).
+				 */
+
 bool desirable(avail_p avp);	/*
 				 * Return whether it is desirable to eliminate
 				 * the recurrences of the expression in avp.
diff --git a/util/ego/cs/cs_vnm.c b/util/ego/cs/cs_vnm.c
index 67507f805..435dd4658 100644
--- a/util/ego/cs/cs_vnm.c
+++ b/util/ego/cs/cs_vnm.c
@@ -20,6 +20,7 @@
 #include "cs_kill.h"
 #include "cs_partit.h"
 #include "cs_getent.h"
+#include "cs_profit.h"
 
 STATIC void push_entity(entity_p enp, line_p lfirst)
 {
@@ -130,6 +131,37 @@ STATIC void push_ternair_op(bblock_p bp, line_p lnp, token_p tkp1,
 	push_avail(av_enter(&av, ocp, TERNAIR_OP), tkp1->tk_lfirst);
 }
 
+STATIC void push_remainder(bblock_p bp, line_p lnp, token_p tkp1, token_p tkp2)
+{
+	/* Enter the implicit division tkp1 / tkp2,
+	 * then push the remainder tkp1 % tkp2.
+	 */
+	struct avail av;
+	occur_p	ocp;
+
+	assert(INSTR(lnp) == op_rmi || INSTR(lnp) == op_rmu);
+	av.av_size = avsize(lnp);
+	av.av_oleft = tkp1->tk_vn;
+	av.av_oright = tkp2->tk_vn;
+
+	/* Check whether we may convert RMI/RMU to DVI/DVU. */
+	if (may_become_dv()) {
+		/* The division is DVI in RMI, or DVU in RMU. */
+		av.av_instr = (INSTR(lnp) == op_rmi ? op_dvi : op_dvu);
+
+		/* In postfix, a b % becomes a b a b / * -.  We must
+		 * keep a and b on the stack, so the first instruction
+		 * to eliminate is lnp, not tkp1->l_first.
+		 */
+		ocp = newoccur(lnp, lnp, bp);
+		av_enter(&av, ocp, BINAIR_OP);
+	}
+
+	av.av_instr = INSTR(lnp);
+	ocp = newoccur(tkp1->tk_lfirst, lnp, bp);
+	push_avail(av_enter(&av, ocp, REMAINDER), tkp1->tk_lfirst);
+}
+
 STATIC void fiddle_stack(line_p lnp)
 {
 	/* The instruction in lnp does something to the valuenumber-stack. */
@@ -317,6 +349,11 @@ void vnm(bblock_p bp)
 				Pop(&tk1, op13size(lnp));
 				push_ternair_op(bp, lnp, &tk1, &tk2, &tk3);
 				break;
+			case REMAINDER:
+				Pop(&tk2, op22size(lnp));
+				Pop(&tk1, op12size(lnp));
+				push_remainder(bp, lnp, &tk1, &tk2);
+				break;
 			case KILL_ENTITY:
 				kill_direct(rep);
 				break;
diff --git a/util/ego/descr/em22.descr b/util/ego/descr/em22.descr
index f995d631c..d9c39226b 100644
--- a/util/ego/descr/em22.descr
+++ b/util/ego/descr/em22.descr
@@ -78,6 +78,7 @@ cheap operations: -1
                   -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:   -1
                                                 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/em24.descr b/util/ego/descr/em24.descr
index a95751170..cbe0ab5c3 100644
--- a/util/ego/descr/em24.descr
+++ b/util/ego/descr/em24.descr
@@ -78,6 +78,7 @@ cheap operations: -1
                   -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:   -1
                                                 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/em44.descr b/util/ego/descr/em44.descr
index 117f26591..b6dbebba3 100644
--- a/util/ego/descr/em44.descr
+++ b/util/ego/descr/em44.descr
@@ -78,6 +78,7 @@ cheap operations: -1
                   -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:   -1
                                                 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/i386.descr b/util/ego/descr/i386.descr
index 264151a60..d5a2014bf 100644
--- a/util/ego/descr/i386.descr
+++ b/util/ego/descr/i386.descr
@@ -93,6 +93,7 @@ cheap operations: op_cii op_cui op_ciu op_cuu -1
                   op_cii op_cui op_ciu op_cuu -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:   -1
                                                 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/i86.descr b/util/ego/descr/i86.descr
index 8be3ec23e..9b27cf840 100644
--- a/util/ego/descr/i86.descr
+++ b/util/ego/descr/i86.descr
@@ -93,6 +93,7 @@ cheap operations: op_cii op_cui op_ciu op_cuu -1
                   op_cii op_cui op_ciu op_cuu -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:   -1
                                                 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/m68020.descr b/util/ego/descr/m68020.descr
index 9d2f46b2b..f568e00e2 100644
--- a/util/ego/descr/m68020.descr
+++ b/util/ego/descr/m68020.descr
@@ -102,6 +102,7 @@ cheap operations: op_cii op_ciu op_cui op_cuu op_cmi op_cmu op_cmp -1
 		  op_cii op_ciu op_cui op_cuu op_cmi op_cmu op_cmp -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:	1 2 3 -1
 						1 2 3 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/m68k2.descr b/util/ego/descr/m68k2.descr
index 58e433db8..6b144cba0 100644
--- a/util/ego/descr/m68k2.descr
+++ b/util/ego/descr/m68k2.descr
@@ -99,6 +99,7 @@ addressing modes: op_adp op_lof op_ldf op_loi op_dch op_lpb -1
 cheap operations: -1 -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:	-1
 						-1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/m68k4.descr b/util/ego/descr/m68k4.descr
index 8e1da4c5e..6b9d23dfa 100644
--- a/util/ego/descr/m68k4.descr
+++ b/util/ego/descr/m68k4.descr
@@ -102,6 +102,7 @@ cheap operations: op_ciu op_cui op_cuu op_cmi op_cmu op_cmp -1
 		  op_ciu op_cui op_cuu op_cmi op_cmu op_cmp -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:	-1
 						-1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/pdp.descr b/util/ego/descr/pdp.descr
index e73b3aaf1..ec8f3abca 100644
--- a/util/ego/descr/pdp.descr
+++ b/util/ego/descr/pdp.descr
@@ -92,6 +92,7 @@ cheap operations: op_cii op_cui op_cfi op_ciu op_cff op_cuu op_cif -1
 		  op_cii op_cui op_cfi op_ciu op_cff op_cuu op_cif -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:	-1
 						-1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/powerpc.descr b/util/ego/descr/powerpc.descr
index 5fb9bb628..cf613e96c 100644
--- a/util/ego/descr/powerpc.descr
+++ b/util/ego/descr/powerpc.descr
@@ -141,6 +141,7 @@ cheap operations: op_cii op_ciu op_cui op_cuu op_cmi op_cmu op_cmp -1
 		  op_cii op_ciu op_cui op_cuu op_cmi op_cmu op_cmp -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: yes yes
 do not eliminate sli if index on shiftcounts:	-1
 						-1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/sparc.descr b/util/ego/descr/sparc.descr
index 978c39ba3..79c33decb 100644
--- a/util/ego/descr/sparc.descr
+++ b/util/ego/descr/sparc.descr
@@ -100,6 +100,7 @@ cheap operations: op_cuu op_ciu op_cui op_cii -1
                   op_cuu op_ciu op_cui op_cii -1
 lexical tresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:   -1
                                                 -1
 forbidden operators: -1 -1
diff --git a/util/ego/descr/vax4.descr b/util/ego/descr/vax4.descr
index 5a39ea759..beaf0c427 100644
--- a/util/ego/descr/vax4.descr
+++ b/util/ego/descr/vax4.descr
@@ -113,6 +113,7 @@ cheap operations: op_cii op_cui op_cfi op_ciu op_cff op_cuu op_cif
 		  op_cmi op_cmu op_cmf op_cms op_cmp -1
 lexical thresholds: 1 1
 indirection limit: 8
+convert remainder to division?: no no
 do not eliminate sli if index on shiftcounts:	1 2 3 -1
 						1 2 3 -1
 forbidden operators: -1 -1