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cmd/internal/obj/ppc64: improve long conditional branch fixup

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Improve the code which fixes up conditional branches which exceed the
range of a single instruction by inserting one extra jump when
possible instead of two.

Change-Id: Ib0eb5b0f47f7d0e0ccd55471307a5f73fbda88a9
Reviewed-on: https://go-review.googlesource.com/c/go/+/342930
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Paul E. Murphy 2021-03-09 16:55:18 -06:00 committed by Lynn Boger
parent 5670ff4ae5
commit 8f397bc118
2 changed files with 73 additions and 26 deletions
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11
src/cmd/internal/obj/ppc64/a.out.go
View File

@ -329,18 +329,13 @@ const (
BI_OVF = 3
)
// Values for the BO field. Add the branch type to
// the likely bits, if a likely setting is known.
// If branch likely or unlikely is not known, don't set it.
// e.g. branch on cr+likely = 15
// Common values for the BO field.
const (
BO_BCTR = 16 // branch on ctr value
BO_BCTR = 16 // decrement ctr, branch on ctr != 0
BO_BCR = 12 // branch on cr value
BO_BCRBCTR = 8 // branch on ctr and cr value
BO_BCRBCTR = 8 // decrement ctr, branch on ctr != 0 and cr value
BO_NOTBCR = 4 // branch on not cr value
BO_UNLIKELY = 2 // value for unlikely
BO_LIKELY = 3 // value for likely
)
// Bit settings from the CR

60
src/cmd/internal/obj/ppc64/asm9.go
View File

@ -642,6 +642,7 @@ func span9(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
var otxt int64
var q *obj.Prog
var out [6]uint32
for bflag != 0 {
bflag = 0
pc = 0
@ -653,6 +654,60 @@ func span9(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
if (o.type_ == 16 || o.type_ == 17) && p.To.Target() != nil {
otxt = p.To.Target().Pc - pc
if otxt < -(1<<15)+10 || otxt >= (1<<15)-10 {
// Assemble the instruction with a target not too far to figure out BI and BO fields.
// If only the CTR or BI (the CR bit) are tested, the conditional branch can be inverted,
// and only one extra branch is needed to reach the target.
tgt := p.To.Target()
p.To.SetTarget(p.Link)
c.asmout(p, o, out[:])
p.To.SetTarget(tgt)
bo := int64(out[0]>>21) & 31
bi := int16((out[0] >> 16) & 31)
invertible := false
if bo&0x14 == 0x14 {
// A conditional branch that is unconditionally taken. This cannot be inverted.
} else if bo&0x10 == 0x10 {
// A branch based on the value of CTR. Invert the CTR comparison against zero bit.
bo ^= 0x2
invertible = true
} else if bo&0x04 == 0x04 {
// A branch based on CR bit. Invert the BI comparison bit.
bo ^= 0x8
invertible = true
}
if invertible {
// Rewrite
// BC bo,...,far_away_target
// NEXT_INSN
// to:
// BC invert(bo),next_insn
// JMP far_away_target
// next_insn:
// NEXT_INSN
p.As = ABC
p.From = obj.Addr{Type: obj.TYPE_CONST, Name: obj.NAME_NONE, Offset: bo}
q = c.newprog()
q.As = ABR
q.To.Type = obj.TYPE_BRANCH
q.To.SetTarget(p.To.Target())
q.Link = p.Link
p.To.SetTarget(p.Link)
p.Link = q
p.Reg = bi // TODO: This is a hack since BI bits are not enumerated as registers
} else {
// Rewrite
// BC ...,far_away_target
// NEXT_INSN
// to
// BC ...,tmp
// JMP next_insn
// tmp:
// JMP far_away_target
// next_insn:
// NEXT_INSN
q = c.newprog()
q.Link = p.Link
p.Link = q
@ -666,9 +721,7 @@ func span9(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q.As = ABR
q.To.Type = obj.TYPE_BRANCH
q.To.SetTarget(q.Link.Link)
//addnop(p->link);
//addnop(p);
}
bflag = 1
}
}
@ -706,7 +759,6 @@ func span9(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
bp := c.cursym.P
var i int32
var out [6]uint32
for p := c.cursym.Func().Text.Link; p != nil; p = p.Link {
c.pc = p.Pc
o = c.oplook(p)