ggen.go

Documentation: cmd/compile/internal/amd64

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package amd64
     6  
     7  import (
     8  	"cmd/compile/internal/ir"
     9  	"cmd/compile/internal/objw"
    10  	"cmd/compile/internal/types"
    11  	"cmd/internal/obj"
    12  	"cmd/internal/obj/x86"
    13  	"internal/buildcfg"
    14  )
    15  
    16  // no floating point in note handlers on Plan 9
    17  var isPlan9 = buildcfg.GOOS == "plan9"
    18  
    19  // DUFFZERO consists of repeated blocks of 4 MOVUPSs + LEAQ,
    20  // See runtime/mkduff.go.
    21  const (
    22  	dzBlocks    = 16 // number of MOV/ADD blocks
    23  	dzBlockLen  = 4  // number of clears per block
    24  	dzBlockSize = 23 // size of instructions in a single block
    25  	dzMovSize   = 5  // size of single MOV instruction w/ offset
    26  	dzLeaqSize  = 4  // size of single LEAQ instruction
    27  	dzClearStep = 16 // number of bytes cleared by each MOV instruction
    28  
    29  	dzClearLen = dzClearStep * dzBlockLen // bytes cleared by one block
    30  	dzSize     = dzBlocks * dzBlockSize
    31  )
    32  
    33  // dzOff returns the offset for a jump into DUFFZERO.
    34  // b is the number of bytes to zero.
    35  func dzOff(b int64) int64 {
    36  	off := int64(dzSize)
    37  	off -= b / dzClearLen * dzBlockSize
    38  	tailLen := b % dzClearLen
    39  	if tailLen >= dzClearStep {
    40  		off -= dzLeaqSize + dzMovSize*(tailLen/dzClearStep)
    41  	}
    42  	return off
    43  }
    44  
    45  // duffzeroDI returns the pre-adjustment to DI for a call to DUFFZERO.
    46  // b is the number of bytes to zero.
    47  func dzDI(b int64) int64 {
    48  	tailLen := b % dzClearLen
    49  	if tailLen < dzClearStep {
    50  		return 0
    51  	}
    52  	tailSteps := tailLen / dzClearStep
    53  	return -dzClearStep * (dzBlockLen - tailSteps)
    54  }
    55  
    56  func zerorange(pp *objw.Progs, p *obj.Prog, off, cnt int64, state *uint32) *obj.Prog {
    57  	const (
    58  		r13 = 1 << iota // if R13 is already zeroed.
    59  	)
    60  
    61  	if cnt == 0 {
    62  		return p
    63  	}
    64  
    65  	if cnt == 8 {
    66  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_MEM, x86.REG_SP, off)
    67  	} else if !isPlan9 && cnt <= int64(8*types.RegSize) {
    68  		for i := int64(0); i < cnt/16; i++ {
    69  			p = pp.Append(p, x86.AMOVUPS, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_MEM, x86.REG_SP, off+i*16)
    70  		}
    71  
    72  		if cnt%16 != 0 {
    73  			p = pp.Append(p, x86.AMOVUPS, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_MEM, x86.REG_SP, off+cnt-int64(16))
    74  		}
    75  	} else if !isPlan9 && (cnt <= int64(128*types.RegSize)) {
    76  		// Save DI to r12. With the amd64 Go register abi, DI can contain
    77  		// an incoming parameter, whereas R12 is always scratch.
    78  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_DI, 0, obj.TYPE_REG, x86.REG_R12, 0)
    79  		// Emit duffzero call
    80  		p = pp.Append(p, leaptr, obj.TYPE_MEM, x86.REG_SP, off+dzDI(cnt), obj.TYPE_REG, x86.REG_DI, 0)
    81  		p = pp.Append(p, obj.ADUFFZERO, obj.TYPE_NONE, 0, 0, obj.TYPE_ADDR, 0, dzOff(cnt))
    82  		p.To.Sym = ir.Syms.Duffzero
    83  		if cnt%16 != 0 {
    84  			p = pp.Append(p, x86.AMOVUPS, obj.TYPE_REG, x86.REG_X15, 0, obj.TYPE_MEM, x86.REG_DI, -int64(8))
    85  		}
    86  		// Restore DI from r12
    87  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_R12, 0, obj.TYPE_REG, x86.REG_DI, 0)
    88  
    89  	} else {
    90  		// When the register ABI is in effect, at this point in the
    91  		// prolog we may have live values in all of RAX,RDI,RCX. Save
    92  		// them off to registers before the REPSTOSQ below, then
    93  		// restore. Note that R12 and R13 are always available as
    94  		// scratch regs; here we also use R15 (this is safe to do
    95  		// since there won't be any globals accessed in the prolog).
    96  		// See rewriteToUseGot() in obj6.go for more on r15 use.
    97  
    98  		// Save rax/rdi/rcx
    99  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_DI, 0, obj.TYPE_REG, x86.REG_R12, 0)
   100  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_AX, 0, obj.TYPE_REG, x86.REG_R13, 0)
   101  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_CX, 0, obj.TYPE_REG, x86.REG_R15, 0)
   102  
   103  		// Set up the REPSTOSQ and kick it off.
   104  		p = pp.Append(p, x86.AXORL, obj.TYPE_REG, x86.REG_AX, 0, obj.TYPE_REG, x86.REG_AX, 0)
   105  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_CONST, 0, cnt/int64(types.RegSize), obj.TYPE_REG, x86.REG_CX, 0)
   106  		p = pp.Append(p, leaptr, obj.TYPE_MEM, x86.REG_SP, off, obj.TYPE_REG, x86.REG_DI, 0)
   107  		p = pp.Append(p, x86.AREP, obj.TYPE_NONE, 0, 0, obj.TYPE_NONE, 0, 0)
   108  		p = pp.Append(p, x86.ASTOSQ, obj.TYPE_NONE, 0, 0, obj.TYPE_NONE, 0, 0)
   109  
   110  		// Restore rax/rdi/rcx
   111  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_R12, 0, obj.TYPE_REG, x86.REG_DI, 0)
   112  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_R13, 0, obj.TYPE_REG, x86.REG_AX, 0)
   113  		p = pp.Append(p, x86.AMOVQ, obj.TYPE_REG, x86.REG_R15, 0, obj.TYPE_REG, x86.REG_CX, 0)
   114  
   115  		// Record the fact that r13 is no longer zero.
   116  		*state &= ^uint32(r13)
   117  	}
   118  
   119  	return p
   120  }
   121  
   122  func ginsnop(pp *objw.Progs) *obj.Prog {
   123  	// This is a hardware nop (1-byte 0x90) instruction,
   124  	// even though we describe it as an explicit XCHGL here.
   125  	// Particularly, this does not zero the high 32 bits
   126  	// like typical *L opcodes.
   127  	// (gas assembles "xchg %eax,%eax" to 0x87 0xc0, which
   128  	// does zero the high 32 bits.)
   129  	p := pp.Prog(x86.AXCHGL)
   130  	p.From.Type = obj.TYPE_REG
   131  	p.From.Reg = x86.REG_AX
   132  	p.To.Type = obj.TYPE_REG
   133  	p.To.Reg = x86.REG_AX
   134  	return p
   135  }
   136
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