cmd/gc: support for "portable" optimization logic

Code in gc/popt.c is compiled as part of 5g, 6g, and 8g,
meaning it can use arch-specific headers but there's
just one copy of the code.

This is the same arrangement we use for the portable
code generation logic in gc/pgen.c.

Move fixjmp and noreturn there to get the ball rolling.

R=ken2
CC=golang-dev
https://golang.org/cl/12789043

src/cmd/5g/gg.h

@@ -39,7 +39,7 @@ struct	Prog
 	uint32	loc;		// pc offset in this func
 	uint32	lineno;		// source line that generated this
 	Prog*	link;		// next instruction in this func
-	void*	regp;		// points to enclosing Reg struct
+	void*	opt;		// for optimizer passes
 	short	as;		// opcode
 	uchar	reg;		// doubles as width in DATA op
 	uchar	scond;

src/cmd/5g/opt.h

@@ -28,6 +28,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#include	"../gc/popt.h"
+
 #define	Z	N
 #define	Adr	Addr
 
@@ -50,7 +52,7 @@ typedef	struct	Rgn	Rgn;
 // A Reg is a wrapper around a single Prog (one instruction) that holds
 // register optimization information while the optimizer runs.
 // r->prog is the instruction.
-// r->prog->regp points back to r.
+// r->prog->opt points back to r.
 struct	Reg
 {
 
@@ -140,7 +142,6 @@ uint32	paint2(Reg*, int);
 void	paint3(Reg*, int, int32, int);
 void	addreg(Adr*, int);
 void	dumpit(char *str, Reg *r0);
-int	noreturn(Prog *p);
 
 /*
  * peep.c
@@ -217,3 +218,10 @@ enum
 };
 
 void proginfo(ProgInfo*, Prog*);
+
+// To allow use of AJMP and ACALL in ../gc/popt.c.
+enum
+{
+	AJMP = AB,
+	ACALL = ABL,
+};

src/cmd/5g/peep.c

@@ -69,7 +69,7 @@ peep(void)
 			r2->link = r1;
 
 			r2->prog = p;
-			p->regp = r2;
+			p->opt = r2;
 
 			r2->p1 = r;
 			r->s1 = r2;

src/cmd/5g/prog.c

@@ -26,6 +26,8 @@ static ProgInfo progtable[ALAST] = {
 	[ATEXT]=	{Pseudo},
 	[AFUNCDATA]=	{Pseudo},
 	[APCDATA]=	{Pseudo},
+	[AUNDEF]=	{OK},
+	[AUSEFIELD]=	{OK},
 
 	// NOP is an internal no-op that also stands
 	// for USED and SET annotations, not the Intel opcode.

src/cmd/5g/reg.c

@@ -36,14 +36,10 @@
 
 #define	NREGVAR	32
 #define	REGBITS	((uint32)0xffffffff)
-#define	P2R(p)	(Reg*)(p->reg)
 
 	void	addsplits(void);
-	int	noreturn(Prog *p);
 static	int	first	= 0;
 
-static	void	fixjmp(Prog*);
-
 
 Reg*
 rega(void)
@@ -260,7 +256,7 @@ regopt(Prog *firstp)
 			lastr = r;
 		}
 		r->prog = p;
-		p->regp = r;
+		p->opt = r;
 
 		r1 = r->p1;
 		if(r1 != R) {
@@ -329,7 +325,7 @@ regopt(Prog *firstp)
 		if(p->to.type == D_BRANCH) {
 			if(p->to.u.branch == P)
 				fatal("pnil %P", p);
-			r1 = p->to.u.branch->regp;
+			r1 = p->to.u.branch->opt;
 			if(r1 == R)
 				fatal("rnil %P", p);
 			if(r1 == r) {
@@ -1467,31 +1463,6 @@ BtoF(int32 b)
 	return bitno(b) - 16;
 }
 
-static Sym*	symlist[10];
-
-int
-noreturn(Prog *p)
-{
-	Sym *s;
-	int i;
-
-	if(symlist[0] == S) {
-		symlist[0] = pkglookup("panicindex", runtimepkg);
-		symlist[1] = pkglookup("panicslice", runtimepkg);
-		symlist[2] = pkglookup("throwinit", runtimepkg);
-		symlist[3] = pkglookup("panic", runtimepkg);
-		symlist[4] = pkglookup("panicwrap", runtimepkg);
-	}
-
-	s = p->to.sym;
-	if(s == S)
-		return 0;
-	for(i=0; symlist[i]!=S; i++)
-		if(s == symlist[i])
-			return 1;
-	return 0;
-}
-
 void
 dumpone(Reg *r)
 {
@@ -1559,123 +1530,3 @@ dumpit(char *str, Reg *r0)
 //		}
 	}
 }
-
-/*
- * the code generator depends on being able to write out JMP (B)
- * instructions that it can jump to now but fill in later.
- * the linker will resolve them nicely, but they make the code
- * longer and more difficult to follow during debugging.
- * remove them.
- */
-
-/* what instruction does a JMP to p eventually land on? */
-static Prog*
-chasejmp(Prog *p, int *jmploop)
-{
-	int n;
-
-	n = 0;
-	while(p != P && p->as == AB && p->to.type == D_BRANCH) {
-		if(++n > 10) {
-			*jmploop = 1;
-			break;
-		}
-		p = p->to.u.branch;
-	}
-	return p;
-}
-
-/*
- * reuse reg pointer for mark/sweep state.
- * leave reg==nil at end because alive==nil.
- */
-#define alive ((void*)0)
-#define dead ((void*)1)
-
-/* mark all code reachable from firstp as alive */
-static void
-mark(Prog *firstp)
-{
-	Prog *p;
-	
-	for(p=firstp; p; p=p->link) {
-		if(p->regp != dead)
-			break;
-		p->regp = alive;
-		if(p->as != ABL && p->to.type == D_BRANCH && p->to.u.branch)
-			mark(p->to.u.branch);
-		if(p->as == AB || p->as == ARET || (p->as == ABL && noreturn(p)))
-			break;
-	}
-}
-
-static void
-fixjmp(Prog *firstp)
-{
-	int jmploop;
-	Prog *p, *last;
-	
-	if(debug['R'] && debug['v'])
-		print("\nfixjmp\n");
-
-	// pass 1: resolve jump to B, mark all code as dead.
-	jmploop = 0;
-	for(p=firstp; p; p=p->link) {
-		if(debug['R'] && debug['v'])
-			print("%P\n", p);
-		if(p->as != ABL && p->to.type == D_BRANCH && p->to.u.branch && p->to.u.branch->as == AB) {
-			p->to.u.branch = chasejmp(p->to.u.branch, &jmploop);
-			if(debug['R'] && debug['v'])
-				print("->%P\n", p);
-		}
-		p->regp = dead;
-	}
-	if(debug['R'] && debug['v'])
-		print("\n");
-	
-	// pass 2: mark all reachable code alive
-	mark(firstp);
-	
-	// pass 3: delete dead code (mostly JMPs).
-	last = nil;
-	for(p=firstp; p; p=p->link) {
-		if(p->regp == dead) {
-			if(p->link == P && p->as == ARET && last && last->as != ARET) {
-				// This is the final ARET, and the code so far doesn't have one.
-				// Let it stay.
-			} else {
-				if(debug['R'] && debug['v'])
-					print("del %P\n", p);
-				continue;
-			}
-		}
-		if(last)
-			last->link = p;
-		last = p;
-	}
-	last->link = P;
-	
-	// pass 4: elide JMP to next instruction.
-	// only safe if there are no jumps to JMPs anymore.
-	if(!jmploop) {
-		last = nil;
-		for(p=firstp; p; p=p->link) {
-			if(p->as == AB && p->to.type == D_BRANCH && p->to.u.branch == p->link) {
-				if(debug['R'] && debug['v'])
-					print("del %P\n", p);
-				continue;
-			}
-			if(last)
-				last->link = p;
-			last = p;
-		}
-		last->link = P;
-	}
-	
-	if(debug['R'] && debug['v']) {
-		print("\n");
-		for(p=firstp; p; p=p->link)
-			print("%P\n", p);
-		print("\n");
-	}
-}

src/cmd/6g/gg.h

@@ -41,7 +41,7 @@ struct	Prog
 	Addr	from;		// src address
 	Addr	to;		// dst address
 	Prog*	link;		// next instruction in this func
-	void*	reg;		// pointer to containing Reg struct
+	void*	opt;		// for optimizer passes
 };
 
 #define TEXTFLAG from.scale

src/cmd/6g/opt.h

@@ -28,6 +28,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#include	"../gc/popt.h"
+
 #define	Z	N
 #define	Adr	Addr
 
@@ -50,7 +52,7 @@ typedef	struct	Rgn	Rgn;
 // A Reg is a wrapper around a single Prog (one instruction) that holds
 // register optimization information while the optimizer runs.
 // r->prog is the instruction.
-// r->prog->regp points back to r.
+// r->prog->opt points back to r.
 struct	Reg
 {
 
@@ -141,7 +143,6 @@ void	paint3(Reg*, int, int32, int);
 void	addreg(Adr*, int);
 void	dumpone(Reg*);
 void	dumpit(char*, Reg*);
-int	noreturn(Prog *p);
 
 /*
  * peep.c

src/cmd/6g/peep.c

@@ -102,7 +102,7 @@ peep(void)
 			r2->link = r1;
 
 			r2->prog = p;
-			p->reg = r2;
+			p->opt = r2;
 
 			r2->p1 = r;
 			r->s1 = r2;

src/cmd/6g/prog.c

@@ -38,12 +38,13 @@ static ProgInfo progtable[ALAST] = {
 	[ATEXT]=	{Pseudo},
 	[AFUNCDATA]=	{Pseudo},
 	[APCDATA]=	{Pseudo},
+	[AUNDEF]=	{OK},
+	[AUSEFIELD]=	{OK},
 
 	// NOP is an internal no-op that also stands
 	// for USED and SET annotations, not the Intel opcode.
 	[ANOP]=		{LeftRead | RightWrite},
 
-
 	[AADCL]=	{SizeL | LeftRead | RightRdwr | SetCarry | UseCarry},
 	[AADCQ]=	{SizeQ | LeftRead | RightRdwr | SetCarry | UseCarry},
 	[AADCW]=	{SizeW | LeftRead | RightRdwr | SetCarry | UseCarry},
@@ -269,10 +270,6 @@ static ProgInfo progtable[ALAST] = {
 	[AUCOMISD]=	{SizeD | LeftRead | RightRead},
 	[AUCOMISS]=	{SizeF | LeftRead | RightRead},
 
-	[AUNDEF]=	{OK},
-
-	[AUSEFIELD]=	{OK},
-
 	[AXCHGB]=	{SizeB | LeftRdwr | RightRdwr},
 	[AXCHGL]=	{SizeL | LeftRdwr | RightRdwr},
 	[AXCHGQ]=	{SizeQ | LeftRdwr | RightRdwr},

src/cmd/6g/reg.c

@@ -35,7 +35,6 @@
 
 #define	NREGVAR	32	/* 16 general + 16 floating */
 #define	REGBITS	((uint32)0xffffffff)
-#define	P2R(p)	(Reg*)(p->reg)
 
 static	int	first	= 1;
 
@@ -153,8 +152,6 @@ static char* regname[] = {
 
 static Node* regnodes[NREGVAR];
 
-static void fixjmp(Prog*);
-
 void
 regopt(Prog *firstp)
 {
@@ -234,7 +231,7 @@ regopt(Prog *firstp)
 			lastr = r;
 		}
 		r->prog = p;
-		p->reg = r;
+		p->opt = r;
 
 		r1 = r->p1;
 		if(r1 != R) {
@@ -305,7 +302,7 @@ regopt(Prog *firstp)
 		if(p->to.type == D_BRANCH) {
 			if(p->to.u.branch == P)
 				fatal("pnil %P", p);
-			r1 = p->to.u.branch->reg;
+			r1 = p->to.u.branch->opt;
 			if(r1 == R)
 				fatal("rnil %P", p);
 			if(r1 == r) {
@@ -1400,148 +1397,3 @@ dumpit(char *str, Reg *r0)
 //		}
 	}
 }
-
-static Sym*	symlist[10];
-
-int
-noreturn(Prog *p)
-{
-	Sym *s;
-	int i;
-
-	if(symlist[0] == S) {
-		symlist[0] = pkglookup("panicindex", runtimepkg);
-		symlist[1] = pkglookup("panicslice", runtimepkg);
-		symlist[2] = pkglookup("throwinit", runtimepkg);
-		symlist[3] = pkglookup("panic", runtimepkg);
-		symlist[4] = pkglookup("panicwrap", runtimepkg);
-	}
-
-	s = p->to.sym;
-	if(s == S)
-		return 0;
-	for(i=0; symlist[i]!=S; i++)
-		if(s == symlist[i])
-			return 1;
-	return 0;
-}
-
-/*
- * the code generator depends on being able to write out JMP
- * instructions that it can jump to now but fill in later.
- * the linker will resolve them nicely, but they make the code
- * longer and more difficult to follow during debugging.
- * remove them.
- */
-
-/* what instruction does a JMP to p eventually land on? */
-static Prog*
-chasejmp(Prog *p, int *jmploop)
-{
-	int n;
-
-	n = 0;
-	while(p != P && p->as == AJMP && p->to.type == D_BRANCH) {
-		if(++n > 10) {
-			*jmploop = 1;
-			break;
-		}
-		p = p->to.u.branch;
-	}
-	return p;
-}
-
-/*
- * reuse reg pointer for mark/sweep state.
- * leave reg==nil at end because alive==nil.
- */
-#define alive ((void*)0)
-#define dead ((void*)1)
-
-/* mark all code reachable from firstp as alive */
-static void
-mark(Prog *firstp)
-{
-	Prog *p;
-	
-	for(p=firstp; p; p=p->link) {
-		if(p->reg != dead)
-			break;
-		p->reg = alive;
-		if(p->as != ACALL && p->to.type == D_BRANCH && p->to.u.branch)
-			mark(p->to.u.branch);
-		if(p->as == AJMP || p->as == ARET || p->as == AUNDEF)
-			break;
-	}
-}
-
-static void
-fixjmp(Prog *firstp)
-{
-	int jmploop;
-	Prog *p, *last;
-	
-	if(debug['R'] && debug['v'])
-		print("\nfixjmp\n");
-
-	// pass 1: resolve jump to AJMP, mark all code as dead.
-	jmploop = 0;
-	for(p=firstp; p; p=p->link) {
-		if(debug['R'] && debug['v'])
-			print("%P\n", p);
-		if(p->as != ACALL && p->to.type == D_BRANCH && p->to.u.branch && p->to.u.branch->as == AJMP) {
-			p->to.u.branch = chasejmp(p->to.u.branch, &jmploop);
-			if(debug['R'] && debug['v'])
-				print("->%P\n", p);
-		}
-		p->reg = dead;
-	}
-	if(debug['R'] && debug['v'])
-		print("\n");
-
-	// pass 2: mark all reachable code alive
-	mark(firstp);
-	
-	// pass 3: delete dead code (mostly JMPs).
-	last = nil;
-	for(p=firstp; p; p=p->link) {
-		if(p->reg == dead) {
-			if(p->link == P && p->as == ARET && last && last->as != ARET) {
-				// This is the final ARET, and the code so far doesn't have one.
-				// Let it stay.
-			} else {
-				if(debug['R'] && debug['v'])
-					print("del %P\n", p);
-				continue;
-			}
-		}
-		if(last)
-			last->link = p;
-		last = p;
-	}
-	last->link = P;
-	
-	// pass 4: elide JMP to next instruction.
-	// only safe if there are no jumps to JMPs anymore.
-	if(!jmploop) {
-		last = nil;
-		for(p=firstp; p; p=p->link) {
-			if(p->as == AJMP && p->to.type == D_BRANCH && p->to.u.branch == p->link) {
-				if(debug['R'] && debug['v'])
-					print("del %P\n", p);
-				continue;
-			}
-			if(last)
-				last->link = p;
-			last = p;
-		}
-		last->link = P;
-	}
-	
-	if(debug['R'] && debug['v']) {
-		print("\n");
-		for(p=firstp; p; p=p->link)
-			print("%P\n", p);
-		print("\n");
-	}
-}

src/cmd/8g/gg.h

@@ -42,7 +42,7 @@ struct	Prog
 	Addr	from;		// src address
 	Addr	to;		// dst address
 	Prog*	link;		// next instruction in this func
-	void*	reg;		// pointer to containing Reg struct
+	void*	opt;		// for optimizer passes
 };
 
 #define TEXTFLAG from.scale

src/cmd/8g/opt.h

@@ -28,6 +28,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#include	"../gc/popt.h"
+
 #define	Z	N
 #define	Adr	Addr
 
@@ -50,7 +52,7 @@ typedef	struct	Rgn	Rgn;
 // A Reg is a wrapper around a single Prog (one instruction) that holds
 // register optimization information while the optimizer runs.
 // r->prog is the instruction.
-// r->prog->regp points back to r.
+// r->prog->opt points back to r.
 struct	Reg
 {
 
@@ -141,7 +143,6 @@ void	paint3(Reg*, int, int32, int);
 void	addreg(Adr*, int);
 void	dumpone(Reg*);
 void	dumpit(char*, Reg*);
-int	noreturn(Prog *p);
 
 /*
  * peep.c

src/cmd/8g/peep.c

@@ -99,7 +99,7 @@ peep(void)
 			r2->link = r1;
 
 			r2->prog = p;
-			p->reg = r2;
+			p->opt = r2;
 
 			r2->p1 = r;
 			r->s1 = r2;

src/cmd/8g/prog.c

@@ -38,6 +38,8 @@ static ProgInfo progtable[ALAST] = {
 	[ATEXT]=	{Pseudo},
 	[AFUNCDATA]=	{Pseudo},
 	[APCDATA]=	{Pseudo},
+	[AUNDEF]=	{OK},
+	[AUSEFIELD]=	{OK},
 
 	// NOP is an internal no-op that also stands
 	// for USED and SET annotations, not the Intel opcode.
@@ -287,10 +289,6 @@ static ProgInfo progtable[ALAST] = {
 	[AUCOMISD]=	{SizeD | LeftRead | RightRead},
 	[AUCOMISS]=	{SizeF | LeftRead | RightRead},
 
-	[AUNDEF]=	{OK},
-
-	[AUSEFIELD]=	{OK},
-
 	[AXCHGB]=	{SizeB | LeftRdwr | RightRdwr},
 	[AXCHGL]=	{SizeL | LeftRdwr | RightRdwr},
 	[AXCHGW]=	{SizeW | LeftRdwr | RightRdwr},

src/cmd/8g/reg.c

@@ -35,11 +35,9 @@
 
 #define	NREGVAR	16	/* 8 integer + 8 floating */
 #define	REGBITS	((uint32)0xffff)
-#define	P2R(p)	(Reg*)(p->reg)
 
 static	int	first	= 1;
 
-static	void	fixjmp(Prog*);
 static	void	fixtemp(Prog*);
 
 Reg*
@@ -206,7 +204,7 @@ regopt(Prog *firstp)
 			lastr = r;
 		}
 		r->prog = p;
-		p->reg = r;
+		p->opt = r;
 
 		r1 = r->p1;
 		if(r1 != R) {
@@ -277,7 +275,7 @@ regopt(Prog *firstp)
 		if(p->to.type == D_BRANCH) {
 			if(p->to.u.branch == P)
 				fatal("pnil %P", p);
-			r1 = p->to.u.branch->reg;
+			r1 = p->to.u.branch->opt;
 			if(r1 == R)
 				fatal("rnil %P", p);
 			if(r1 == r) {
@@ -1366,151 +1364,6 @@ dumpit(char *str, Reg *r0)
 	}
 }
 
-static Sym*	symlist[10];
-
-int
-noreturn(Prog *p)
-{
-	Sym *s;
-	int i;
-
-	if(symlist[0] == S) {
-		symlist[0] = pkglookup("panicindex", runtimepkg);
-		symlist[1] = pkglookup("panicslice", runtimepkg);
-		symlist[2] = pkglookup("throwinit", runtimepkg);
-		symlist[3] = pkglookup("panic", runtimepkg);
-		symlist[4] = pkglookup("panicwrap", runtimepkg);
-	}
-
-	s = p->to.sym;
-	if(s == S)
-		return 0;
-	for(i=0; symlist[i]!=S; i++)
-		if(s == symlist[i])
-			return 1;
-	return 0;
-}
-
-/*
- * the code generator depends on being able to write out JMP
- * instructions that it can jump to now but fill in later.
- * the linker will resolve them nicely, but they make the code
- * longer and more difficult to follow during debugging.
- * remove them.
- */
-
-/* what instruction does a JMP to p eventually land on? */
-static Prog*
-chasejmp(Prog *p, int *jmploop)
-{
-	int n;
-
-	n = 0;
-	while(p != P && p->as == AJMP && p->to.type == D_BRANCH) {
-		if(++n > 10) {
-			*jmploop = 1;
-			break;
-		}
-		p = p->to.u.branch;
-	}
-	return p;
-}
-
-/*
- * reuse reg pointer for mark/sweep state.
- * leave reg==nil at end because alive==nil.
- */
-#define alive ((void*)0)
-#define dead ((void*)1)
-
-/* mark all code reachable from firstp as alive */
-static void
-mark(Prog *firstp)
-{
-	Prog *p;
-	
-	for(p=firstp; p; p=p->link) {
-		if(p->reg != dead)
-			break;
-		p->reg = alive;
-		if(p->as != ACALL && p->to.type == D_BRANCH && p->to.u.branch)
-			mark(p->to.u.branch);
-		if(p->as == AJMP || p->as == ARET || p->as == AUNDEF)
-			break;
-	}
-}
-
-static void
-fixjmp(Prog *firstp)
-{
-	int jmploop;
-	Prog *p, *last;
-	
-	if(debug['R'] && debug['v'])
-		print("\nfixjmp\n");
-
-	// pass 1: resolve jump to AJMP, mark all code as dead.
-	jmploop = 0;
-	for(p=firstp; p; p=p->link) {
-		if(debug['R'] && debug['v'])
-			print("%P\n", p);
-		if(p->as != ACALL && p->to.type == D_BRANCH && p->to.u.branch && p->to.u.branch->as == AJMP) {
-			p->to.u.branch = chasejmp(p->to.u.branch, &jmploop);
-			if(debug['R'] && debug['v'])
-				print("->%P\n", p);
-		}
-		p->reg = dead;
-	}
-	if(debug['R'] && debug['v'])
-		print("\n");
-
-	// pass 2: mark all reachable code alive
-	mark(firstp);
-	
-	// pass 3: delete dead code (mostly JMPs).
-	last = nil;
-	for(p=firstp; p; p=p->link) {
-		if(p->reg == dead) {
-			if(p->link == P && p->as == ARET && last && last->as != ARET) {
-				// This is the final ARET, and the code so far doesn't have one.
-				// Let it stay.
-			} else {
-				if(debug['R'] && debug['v'])
-					print("del %P\n", p);
-				continue;
-			}
-		}
-		if(last)
-			last->link = p;
-		last = p;
-	}
-	last->link = P;
-	
-	// pass 4: elide JMP to next instruction.
-	// only safe if there are no jumps to JMPs anymore.
-	if(!jmploop) {
-		last = nil;
-		for(p=firstp; p; p=p->link) {
-			if(p->as == AJMP && p->to.type == D_BRANCH && p->to.u.branch == p->link) {
-				if(debug['R'] && debug['v'])
-					print("del %P\n", p);
-				continue;
-			}
-			if(last)
-				last->link = p;
-			last = p;
-		}
-		last->link = P;
-	}
-	
-	if(debug['R'] && debug['v']) {
-		print("\n");
-		for(p=firstp; p; p=p->link)
-			print("%P\n", p);
-		print("\n");
-	}
-}
-
 static uint32
 fnv1(Sym *sym)
 {

src/cmd/dist/build.c

@@ -489,6 +489,7 @@ static struct {
 	{"cmd/gc", {
 		"-cplx.c",
 		"-pgen.c",
+		"-popt.c",
 		"-y1.tab.c",  // makefile dreg
 		"opnames.h",
 	}},
@@ -513,18 +514,24 @@ static struct {
 	{"cmd/5g", {
 		"../gc/cplx.c",
 		"../gc/pgen.c",
+		"../gc/popt.c",
+		"../gc/popt.h",
 		"../5l/enam.c",
 		"$GOROOT/pkg/obj/$GOOS_$GOARCH/libgc.a",
 	}},
 	{"cmd/6g", {
 		"../gc/cplx.c",
 		"../gc/pgen.c",
+		"../gc/popt.c",
+		"../gc/popt.h",
 		"../6l/enam.c",
 		"$GOROOT/pkg/obj/$GOOS_$GOARCH/libgc.a",
 	}},
 	{"cmd/8g", {
 		"../gc/cplx.c",
 		"../gc/pgen.c",
+		"../gc/popt.c",
+		"../gc/popt.h",
 		"../8l/enam.c",
 		"$GOROOT/pkg/obj/$GOOS_$GOARCH/libgc.a",
 	}},

src/cmd/gc/pgen.c

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// "Portable" code generation.
+// Compiled separately for 5g, 6g, and 8g, so allowed to use gg.h, opt.h.
+// Must code to the intersection of the three back ends.
+
 #include	<u.h>
 #include	<libc.h>
 #include	"gg.h"

src/cmd/gc/popt.c

+// Derived from Inferno utils/6c/reg.c
+// http://code.google.com/p/inferno-os/source/browse/utils/6c/reg.c
+//
+//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
+//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
+//	Portions Copyright © 1997-1999 Vita Nuova Limited
+//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
+//	Portions Copyright © 2004,2006 Bruce Ellis
+//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
+//	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
+//	Portions Copyright © 2009 The Go Authors.  All rights reserved.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+// "Portable" optimizations.
+// Compiled separately for 5g, 6g, and 8g, so allowed to use gg.h, opt.h.
+// Must code to the intersection of the three back ends.
+
+#include	<u.h>
+#include	<libc.h>
+#include	"gg.h"
+#include	"opt.h"
+
+// p is a call instruction. Does the call fail to return?
+int
+noreturn(Prog *p)
+{
+	Sym *s;
+	int i;
+	static Sym*	symlist[10];
+
+	if(symlist[0] == S) {
+		symlist[0] = pkglookup("panicindex", runtimepkg);
+		symlist[1] = pkglookup("panicslice", runtimepkg);
+		symlist[2] = pkglookup("throwinit", runtimepkg);
+		symlist[3] = pkglookup("panic", runtimepkg);
+		symlist[4] = pkglookup("panicwrap", runtimepkg);
+	}
+
+	s = p->to.sym;
+	if(s == S)
+		return 0;
+	for(i=0; symlist[i]!=S; i++)
+		if(s == symlist[i])
+			return 1;
+	return 0;
+}
+
+// JMP chasing and removal.
+//
+// The code generator depends on being able to write out jump
+// instructions that it can jump to now but fill in later.
+// the linker will resolve them nicely, but they make the code
+// longer and more difficult to follow during debugging.
+// Remove them.
+
+/* what instruction does a JMP to p eventually land on? */
+static Prog*
+chasejmp(Prog *p, int *jmploop)
+{
+	int n;
+
+	n = 0;
+	while(p != P && p->as == AJMP && p->to.type == D_BRANCH) {
+		if(++n > 10) {
+			*jmploop = 1;
+			break;
+		}
+		p = p->to.u.branch;
+	}
+	return p;
+}
+
+/*
+ * reuse reg pointer for mark/sweep state.
+ * leave reg==nil at end because alive==nil.
+ */
+#define alive ((void*)0)
+#define dead ((void*)1)
+
+/* mark all code reachable from firstp as alive */
+static void
+mark(Prog *firstp)
+{
+	Prog *p;
+	
+	for(p=firstp; p; p=p->link) {
+		if(p->opt != dead)
+			break;
+		p->opt = alive;
+		if(p->as != ACALL && p->to.type == D_BRANCH && p->to.u.branch)
+			mark(p->to.u.branch);
+		if(p->as == AJMP || p->as == ARET || p->as == AUNDEF)
+			break;
+	}
+}
+
+void
+fixjmp(Prog *firstp)
+{
+	int jmploop;
+	Prog *p, *last;
+	
+	if(debug['R'] && debug['v'])
+		print("\nfixjmp\n");
+
+	// pass 1: resolve jump to jump, mark all code as dead.
+	jmploop = 0;
+	for(p=firstp; p; p=p->link) {
+		if(debug['R'] && debug['v'])
+			print("%P\n", p);
+		if(p->as != ACALL && p->to.type == D_BRANCH && p->to.u.branch && p->to.u.branch->as == AJMP) {
+			p->to.u.branch = chasejmp(p->to.u.branch, &jmploop);
+			if(debug['R'] && debug['v'])
+				print("->%P\n", p);
+		}
+		p->opt = dead;
+	}
+	if(debug['R'] && debug['v'])
+		print("\n");
+
+	// pass 2: mark all reachable code alive
+	mark(firstp);
+	
+	// pass 3: delete dead code (mostly JMPs).
+	last = nil;
+	for(p=firstp; p; p=p->link) {
+		if(p->opt == dead) {
+			if(p->link == P && p->as == ARET && last && last->as != ARET) {
+				// This is the final ARET, and the code so far doesn't have one.
+				// Let it stay.
+			} else {
+				if(debug['R'] && debug['v'])
+					print("del %P\n", p);
+				continue;
+			}
+		}
+		if(last)
+			last->link = p;
+		last = p;
+	}
+	last->link = P;
+	
+	// pass 4: elide JMP to next instruction.
+	// only safe if there are no jumps to JMPs anymore.
+	if(!jmploop) {
+		last = nil;
+		for(p=firstp; p; p=p->link) {
+			if(p->as == AJMP && p->to.type == D_BRANCH && p->to.u.branch == p->link) {
+				if(debug['R'] && debug['v'])
+					print("del %P\n", p);
+				continue;
+			}
+			if(last)
+				last->link = p;
+			last = p;
+		}
+		last->link = P;
+	}
+	
+	if(debug['R'] && debug['v']) {
+		print("\n");
+		for(p=firstp; p; p=p->link)
+			print("%P\n", p);
+		print("\n");
+	}
+}

src/cmd/gc/popt.h

+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+void	fixjmp(Prog*);
+int	noreturn(Prog*);