Golang Prog.From方法代码示例

func progedit(ctxt *obj.Link, p *obj.Prog) {
	// Maintain information about code generation mode.
	if ctxt.Mode == 0 {
		ctxt.Mode = ctxt.Arch.Regsize * 8
	}
	p.Mode = int8(ctxt.Mode)

	switch p.As {
	case AMODE:
		if p.From.Type == obj.TYPE_CONST || (p.From.Type == obj.TYPE_MEM && p.From.Reg == REG_NONE) {
			switch int(p.From.Offset) {
			case 16, 32, 64:
				ctxt.Mode = int(p.From.Offset)
			}
		}
		obj.Nopout(p)
	}

	// Thread-local storage references use the TLS pseudo-register.
	// As a register, TLS refers to the thread-local storage base, and it
	// can only be loaded into another register:
	//
	//         MOVQ TLS, AX
	//
	// An offset from the thread-local storage base is written off(reg)(TLS*1).
	// Semantically it is off(reg), but the (TLS*1) annotation marks this as
	// indexing from the loaded TLS base. This emits a relocation so that
	// if the linker needs to adjust the offset, it can. For example:
	//
	//         MOVQ TLS, AX
	//         MOVQ 0(AX)(TLS*1), CX // load g into CX
	//
	// On systems that support direct access to the TLS memory, this
	// pair of instructions can be reduced to a direct TLS memory reference:
	//
	//         MOVQ 0(TLS), CX // load g into CX
	//
	// The 2-instruction and 1-instruction forms correspond to the two code
	// sequences for loading a TLS variable in the local exec model given in "ELF
	// Handling For Thread-Local Storage".
	//
	// We apply this rewrite on systems that support the 1-instruction form.
	// The decision is made using only the operating system and the -shared flag,
	// not the link mode. If some link modes on a particular operating system
	// require the 2-instruction form, then all builds for that operating system
	// will use the 2-instruction form, so that the link mode decision can be
	// delayed to link time.
	//
	// In this way, all supported systems use identical instructions to
	// access TLS, and they are rewritten appropriately first here in
	// liblink and then finally using relocations in the linker.
	//
	// When -shared is passed, we leave the code in the 2-instruction form but
	// assemble (and relocate) them in different ways to generate the initial
	// exec code sequence. It's a bit of a fluke that this is possible without
	// rewriting the instructions more comprehensively, and it only does because
	// we only support a single TLS variable (g).

	if canuse1insntls(ctxt) {
		// Reduce 2-instruction sequence to 1-instruction sequence.
		// Sequences like
		//	MOVQ TLS, BX
		//	... off(BX)(TLS*1) ...
		// become
		//	NOP
		//	... off(TLS) ...
		//
		// TODO(rsc): Remove the Hsolaris special case. It exists only to
		// guarantee we are producing byte-identical binaries as before this code.
		// But it should be unnecessary.
		if (p.As == AMOVQ || p.As == AMOVL) && p.From.Type == obj.TYPE_REG && p.From.Reg == REG_TLS && p.To.Type == obj.TYPE_REG && REG_AX <= p.To.Reg && p.To.Reg <= REG_R15 && ctxt.Headtype != obj.Hsolaris {
			obj.Nopout(p)
		}
		if p.From.Type == obj.TYPE_MEM && p.From.Index == REG_TLS && REG_AX <= p.From.Reg && p.From.Reg <= REG_R15 {
			p.From.Reg = REG_TLS
			p.From.Scale = 0
			p.From.Index = REG_NONE
		}

		if p.To.Type == obj.TYPE_MEM && p.To.Index == REG_TLS && REG_AX <= p.To.Reg && p.To.Reg <= REG_R15 {
			p.To.Reg = REG_TLS
			p.To.Scale = 0
			p.To.Index = REG_NONE
		}
	} else {
		// load_g_cx, below, always inserts the 1-instruction sequence. Rewrite it
		// as the 2-instruction sequence if necessary.
		//	MOVQ 0(TLS), BX
		// becomes
		//	MOVQ TLS, BX
		//	MOVQ 0(BX)(TLS*1), BX
		if (p.As == AMOVQ || p.As == AMOVL) && p.From.Type == obj.TYPE_MEM && p.From.Reg == REG_TLS && p.To.Type == obj.TYPE_REG && REG_AX <= p.To.Reg && p.To.Reg <= REG_R15 {
			q := obj.Appendp(ctxt, p)
			q.As = p.As
			q.From = p.From
			q.From.Type = obj.TYPE_MEM
			q.From.Reg = p.To.Reg
			q.From.Index = REG_TLS
			q.From.Scale = 2 // TODO: use 1
			q.To = p.To
//.........这里部分代码省略.........

func peep(firstp *obj.Prog) {
	g := (*gc.Graph)(gc.Flowstart(firstp, nil))
	if g == nil {
		return
	}
	gactive = 0

	// byte, word arithmetic elimination.
	elimshortmov(g)

	// constant propagation
	// find MOV $con,R followed by
	// another MOV $con,R without
	// setting R in the interim
	var p *obj.Prog
	for r := (*gc.Flow)(g.Start); r != nil; r = r.Link {
		p = r.Prog
		switch p.As {
		case x86.ALEAL,
			x86.ALEAQ:
			if regtyp(&p.To) {
				if p.From.Sym != nil {
					if p.From.Index == x86.REG_NONE {
						conprop(r)
					}
				}
			}

		case x86.AMOVB,
			x86.AMOVW,
			x86.AMOVL,
			x86.AMOVQ,
			x86.AMOVSS,
			x86.AMOVSD:
			if regtyp(&p.To) {
				if p.From.Type == obj.TYPE_CONST || p.From.Type == obj.TYPE_FCONST {
					conprop(r)
				}
			}
		}
	}

	var r *gc.Flow
	var r1 *gc.Flow
	var p1 *obj.Prog
	var t int
loop1:
	if gc.Debug['P'] != 0 && gc.Debug['v'] != 0 {
		gc.Dumpit("loop1", g.Start, 0)
	}

	t = 0
	for r = g.Start; r != nil; r = r.Link {
		p = r.Prog
		switch p.As {
		case x86.AMOVL,
			x86.AMOVQ,
			x86.AMOVSS,
			x86.AMOVSD:
			if regtyp(&p.To) {
				if regtyp(&p.From) {
					if copyprop(g, r) {
						excise(r)
						t++
					} else if subprop(r) && copyprop(g, r) {
						excise(r)
						t++
					}
				}
			}

		case x86.AMOVBLZX,
			x86.AMOVWLZX,
			x86.AMOVBLSX,
			x86.AMOVWLSX:
			if regtyp(&p.To) {
				r1 = rnops(gc.Uniqs(r))
				if r1 != nil {
					p1 = r1.Prog
					if p.As == p1.As && p.To.Type == p1.From.Type && p.To.Reg == p1.From.Reg {
						p1.As = x86.AMOVL
						t++
					}
				}
			}

		case x86.AMOVBQSX,
			x86.AMOVBQZX,
			x86.AMOVWQSX,
			x86.AMOVWQZX,
			x86.AMOVLQSX,
			x86.AMOVLQZX,
			x86.AMOVQL:
			if regtyp(&p.To) {
				r1 = rnops(gc.Uniqs(r))
				if r1 != nil {
					p1 = r1.Prog
					if p.As == p1.As && p.To.Type == p1.From.Type && p.To.Reg == p1.From.Reg {
						p1.As = x86.AMOVQ
						t++
//.........这里部分代码省略.........