[dev.power64] 9g: implement regopt

This adds registerization support to 9g equivalent to what the
other compilers have.

LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://golang.org/cl/174980043

src/cmd/9g/opt.h

@@ -70,24 +70,40 @@ struct	Reg
 {
 	Flow	f;
 
-	Bits	set;  		// variables written by this instruction.
-	Bits	use1; 		// variables read by prog->from.
-	Bits	use2; 		// variables read by prog->to.
+	Bits	set;  		// regopt variables written by this instruction.
+	Bits	use1; 		// regopt variables read by prog->from.
+	Bits	use2; 		// regopt variables read by prog->to.
 
+	// refahead/refbehind are the regopt variables whose current
+	// value may be used in the following/preceding instructions
+	// up to a CALL (or the value is clobbered).
 	Bits	refbehind;
 	Bits	refahead;
+	// calahead/calbehind are similar, but for variables in
+	// instructions that are reachable after hitting at least one
+	// CALL.
 	Bits	calbehind;
 	Bits	calahead;
 	Bits	regdiff;
 	Bits	act;
 
-	int32	regu;		// register used bitmap
+	uint64	regu;		// register used bitmap
 };
 #define	R	((Reg*)0)
 /*c2go extern Reg *R; */
 
 #define	NRGN	600
 /*c2go enum { NRGN = 600 }; */
+
+// A Rgn represents a single regopt variable over a region of code
+// where a register could potentially be dedicated to that variable.
+// The code encompassed by a Rgn is defined by the flow graph,
+// starting at enter, flood-filling forward while varno is refahead
+// and backward while varno is refbehind, and following branches.  A
+// single variable may be represented by multiple disjoint Rgns and
+// each Rgn may choose a different register for that variable.
+// Registers are allocated to regions greedily in order of descending
+// cost.
 struct	Rgn
 {
 	Reg*	enter;
@@ -104,7 +120,7 @@ EXTERN	Rgn*	rgp;
 EXTERN	int	nregion;
 EXTERN	int	nvar;
 EXTERN	int32	regbits;
-EXTERN	int32	exregbits;
+EXTERN	int32	exregbits;		// TODO(austin) not used; remove
 EXTERN	Bits	externs;
 EXTERN	Bits	params;
 EXTERN	Bits	consts;
@@ -118,10 +134,8 @@ EXTERN	struct
 {
 	int32	ncvtreg;
 	int32	nspill;
-	int32	nreload;
 	int32	ndelmov;
 	int32	nvar;
-	int32	naddr;
 } ostats;
 
 /*
@@ -133,10 +147,10 @@ void	addmove(Reg*, int, int, int);
 Bits	mkvar(Reg*, Adr*);
 void	prop(Reg*, Bits, Bits);
 void	synch(Reg*, Bits);
-uint32	allreg(uint32, Rgn*);
+uint64	allreg(uint64, Rgn*);
 void	paint1(Reg*, int);
-uint32	paint2(Reg*, int);
-void	paint3(Reg*, int, int32, int);
+uint64	paint2(Reg*, int, int);
+void	paint3(Reg*, int, uint64, int);
 void	addreg(Adr*, int);
 void	dumpone(Flow*, int);
 void	dumpit(char*, Flow*, int);
@@ -160,8 +174,8 @@ typedef struct ProgInfo ProgInfo;
 struct ProgInfo
 {
 	uint32 flags; // the bits below
-	uint64 reguse; // required registers used by this instruction
-	uint64 regset; // required registers set by this instruction
+	uint64 reguse; // registers implicitly used by this instruction
+	uint64 regset; // registers implicitly set by this instruction
 	uint64 regindex; // registers used by addressing mode
 };
 
@@ -182,20 +196,21 @@ enum
 	SizeF = 1<<7, // float aka float32
 	SizeD = 1<<8, // double aka float64
 
-	// Left side: address taken, read, write.
+	// Left side (Prog.from): address taken, read, write.
 	LeftAddr = 1<<9,
 	LeftRead = 1<<10,
 	LeftWrite = 1<<11,
 
-	// Register in middle; never written.
+	// Register in middle (Prog.reg); only ever read.
 	RegRead = 1<<12,
 	CanRegRead = 1<<13,
 
-	// Right side: address taken, read, write.
+	// Right side (Prog.to): address taken, read, write.
 	RightAddr = 1<<14,
 	RightRead = 1<<15,
 	RightWrite = 1<<16,
 
+	// Instruction updates whichever of from/to is type D_OREG
 	PostInc = 1<<17,
 
 	// Instruction kinds