From: eric fang Date: Tue, 18 Jan 2022 02:52:08 +0000 (+0000) Subject: cmd/internal/obj/arm64: optimize function prologue/epilogue with STP/LDP X-Git-Tag: go1.19beta1~1115 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=c6d9b38dd82fea8775f1dff9a4a70a017463035d;p=gostls13.git cmd/internal/obj/arm64: optimize function prologue/epilogue with STP/LDP In function prologue and epilogue, we save and restore FP and LR registers, and adjust RSP. The current instruction sequence is as follow. For frame size <= 240B, prologue: MOVD.W R30, -offset(RSP) MOVD R29, -8(RSP) epilogue: MOVD -8(RSP), R29 MOVD.P offset(RSP), R30 For frame size > 240B, prologue: SUB $offset, RSP, R27 MOVD R30, (R27) MOVD R27, RSP MOVD R29, -8(RSP) epilogue: MOVD -8(RSP), R29 MOVD (RSP), R30 ADD $offset, RSP Each sequence uses two load or store instructions, actually we can load or store two registers with one LDP or STP instruction. This CL changes the sequences as follow. For frame size <= 496B, prologue: STP (R29, R30), -(offset+8)(RSP) SUB $offset, RSP, RSP epilogue: LDP -8(RSP), (R29, R30) ADD $offset, RSP, RSP For frame size > 496B, prologue: SUB $offset, RSP, R20 STP (R29, R30), -8(R20) MOVD R20, RSP epilogue: LDP -8(RSP), (R29, R30) ADD $offset, RSP, RSP Change-Id: Ia58af85fc81cce9b7c393dc38df43bffb203baad Reviewed-on: https://go-review.googlesource.com/c/go/+/379075 Reviewed-by: Cherry Mui Trust: Eric Fang Run-TryBot: Eric Fang --- diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go index 2bbc7e37b0..43f7b16d6e 100644 --- a/src/cmd/internal/obj/arm64/obj7.go +++ b/src/cmd/internal/obj/arm64/obj7.go @@ -622,92 +622,124 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) { var prologueEnd *obj.Prog aoffset := c.autosize - if aoffset > 0xF0 { - aoffset = 0xF0 + if aoffset > 0x1f0 { + // LDP offset variant range is -512 to 504, SP should be 16-byte aligned, + // so the maximum aoffset value is 496. + aoffset = 0x1f0 } // Frame is non-empty. Make sure to save link register, even if // it is a leaf function, so that traceback works. q = p if c.autosize > aoffset { - // Frame size is too large for a MOVD.W instruction. - // Store link register before decrementing SP, so if a signal comes - // during the execution of the function prologue, the traceback - // code will not see a half-updated stack frame. - // This sequence is not async preemptible, as if we open a frame - // at the current SP, it will clobber the saved LR. - q = c.ctxt.StartUnsafePoint(q, c.newprog) + // Frame size is too large for a STP instruction. Store the frame pointer + // register and link register before decrementing SP, so if a signal comes + // during the execution of the function prologue, the traceback code will + // not see a half-updated stack frame. - q = obj.Appendp(q, c.newprog) - q.Pos = p.Pos - q.As = ASUB - q.From.Type = obj.TYPE_CONST - q.From.Offset = int64(c.autosize) - q.Reg = REGSP - q.To.Type = obj.TYPE_REG - q.To.Reg = REGTMP + // SUB $autosize, RSP, R20 + q1 = obj.Appendp(q, c.newprog) + q1.Pos = p.Pos + q1.As = ASUB + q1.From.Type = obj.TYPE_CONST + q1.From.Offset = int64(c.autosize) + q1.Reg = REGSP + q1.To.Type = obj.TYPE_REG + q1.To.Reg = REG_R20 - prologueEnd = q + prologueEnd = q1 - q = obj.Appendp(q, c.newprog) - q.Pos = p.Pos - q.As = AMOVD - q.From.Type = obj.TYPE_REG - q.From.Reg = REGLINK - q.To.Type = obj.TYPE_MEM - q.To.Reg = REGTMP + // STP (R29, R30), -8(R20) + q1 = obj.Appendp(q1, c.newprog) + q1.Pos = p.Pos + q1.As = ASTP + q1.From.Type = obj.TYPE_REGREG + q1.From.Reg = REGFP + q1.From.Offset = REGLINK + q1.To.Type = obj.TYPE_MEM + q1.To.Reg = REG_R20 + q1.To.Offset = -8 - q1 = obj.Appendp(q, c.newprog) + // This is not async preemptible, as if we open a frame + // at the current SP, it will clobber the saved LR. + q1 = c.ctxt.StartUnsafePoint(q1, c.newprog) + + // MOVD R20, RSP + q1 = obj.Appendp(q1, c.newprog) q1.Pos = p.Pos q1.As = AMOVD q1.From.Type = obj.TYPE_REG - q1.From.Reg = REGTMP + q1.From.Reg = REG_R20 q1.To.Type = obj.TYPE_REG q1.To.Reg = REGSP q1.Spadj = c.autosize + q1 = c.ctxt.EndUnsafePoint(q1, c.newprog, -1) + if buildcfg.GOOS == "ios" { // iOS does not support SA_ONSTACK. We will run the signal handler // on the G stack. If we write below SP, it may be clobbered by - // the signal handler. So we save LR after decrementing SP. + // the signal handler. So we save FP and LR after decrementing SP. + // STP (R29, R30), -8(RSP) q1 = obj.Appendp(q1, c.newprog) q1.Pos = p.Pos - q1.As = AMOVD - q1.From.Type = obj.TYPE_REG - q1.From.Reg = REGLINK + q1.As = ASTP + q1.From.Type = obj.TYPE_REGREG + q1.From.Reg = REGFP + q1.From.Offset = REGLINK q1.To.Type = obj.TYPE_MEM q1.To.Reg = REGSP + q1.To.Offset = -8 } - - q1 = c.ctxt.EndUnsafePoint(q1, c.newprog, -1) } else { - // small frame, update SP and save LR in a single MOVD.W instruction + // small frame, save FP and LR with one STP instruction, then update SP. + // Store first, so if a signal comes during the execution of the function + // prologue, the traceback code will not see a half-updated stack frame. + // STP (R29, R30), -aoffset-8(RSP) q1 = obj.Appendp(q, c.newprog) - q1.As = AMOVD + q1.As = ASTP q1.Pos = p.Pos - q1.From.Type = obj.TYPE_REG - q1.From.Reg = REGLINK + q1.From.Type = obj.TYPE_REGREG + q1.From.Reg = REGFP + q1.From.Offset = REGLINK q1.To.Type = obj.TYPE_MEM - q1.Scond = C_XPRE - q1.To.Offset = int64(-aoffset) + q1.To.Offset = int64(-aoffset - 8) q1.To.Reg = REGSP - q1.Spadj = aoffset prologueEnd = q1 + + q1 = c.ctxt.StartUnsafePoint(q1, c.newprog) + // This instruction is not async preemptible, see the above comment. + // SUB $aoffset, RSP, RSP + q1 = obj.Appendp(q1, c.newprog) + q1.Pos = p.Pos + q1.As = ASUB + q1.From.Type = obj.TYPE_CONST + q1.From.Offset = int64(aoffset) + q1.Reg = REGSP + q1.To.Type = obj.TYPE_REG + q1.To.Reg = REGSP + q1.Spadj = aoffset + + q1 = c.ctxt.EndUnsafePoint(q1, c.newprog, -1) + + if buildcfg.GOOS == "ios" { + // See the above comment. + // STP (R29, R30), -8(RSP) + q1 = obj.Appendp(q1, c.newprog) + q1.As = ASTP + q1.Pos = p.Pos + q1.From.Type = obj.TYPE_REGREG + q1.From.Reg = REGFP + q1.From.Offset = REGLINK + q1.To.Type = obj.TYPE_MEM + q1.To.Offset = int64(-8) + q1.To.Reg = REGSP + } } prologueEnd.Pos = prologueEnd.Pos.WithXlogue(src.PosPrologueEnd) - // Frame pointer. - q1 = obj.Appendp(q1, c.newprog) - q1.Pos = p.Pos - q1.As = AMOVD - q1.From.Type = obj.TYPE_REG - q1.From.Reg = REGFP - q1.To.Type = obj.TYPE_MEM - q1.To.Reg = REGSP - q1.To.Offset = -8 - q1 = obj.Appendp(q1, c.newprog) q1.Pos = p.Pos q1.As = ASUB @@ -850,48 +882,28 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) { p.To.Reg = REGFP } } else { - /* want write-back pre-indexed SP+autosize -> SP, loading REGLINK*/ - - // Frame pointer. - p.As = AMOVD + aoffset := c.autosize + // LDP -8(RSP), (R29, R30) + p.As = ALDP p.From.Type = obj.TYPE_MEM - p.From.Reg = REGSP p.From.Offset = -8 - p.To.Type = obj.TYPE_REG + p.From.Reg = REGSP + p.To.Type = obj.TYPE_REGREG p.To.Reg = REGFP - p = obj.Appendp(p, c.newprog) - - aoffset := c.autosize + p.To.Offset = REGLINK - if aoffset <= 0xF0 { - p.As = AMOVD - p.From.Type = obj.TYPE_MEM - p.Scond = C_XPOST - p.From.Offset = int64(aoffset) - p.From.Reg = REGSP - p.To.Type = obj.TYPE_REG - p.To.Reg = REGLINK - p.Spadj = -aoffset - } else { - p.As = AMOVD - p.From.Type = obj.TYPE_MEM - p.From.Offset = 0 - p.From.Reg = REGSP - p.To.Type = obj.TYPE_REG - p.To.Reg = REGLINK - - q = newprog() - q.As = AADD - q.From.Type = obj.TYPE_CONST - q.From.Offset = int64(aoffset) - q.To.Type = obj.TYPE_REG - q.To.Reg = REGSP - q.Link = p.Link - q.Spadj = int32(-q.From.Offset) - q.Pos = p.Pos - p.Link = q - p = q - } + // ADD $aoffset, RSP, RSP + q = newprog() + q.As = AADD + q.From.Type = obj.TYPE_CONST + q.From.Offset = int64(aoffset) + q.To.Type = obj.TYPE_REG + q.To.Reg = REGSP + q.Spadj = -aoffset + q.Pos = p.Pos + q.Link = p.Link + p.Link = q + p = q } // If enabled, this code emits 'MOV PC, R27' before every 'MOV LR, PC',