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cmd/compile: single pass over Blocks in Liveness.epilogue 

Currently Liveness.epilogue makes three passes over the Blocks, but
there's no need to do this. Combine them into a single pass. This
eliminates the need for blockEffects.lastbitmapindex, but, more
importantly, will let us incrementally compact the liveness bitmaps
and significantly reduce allocatons in Liveness.epilogue.

Passes toolstash -cmp.

Updates #24543.

Change-Id: I27802bcd00d23aa122a7ec16cdfd739ae12dd7aa
Reviewed-on: https://go-review.googlesource.com/110175
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Austin Clements 2018-04-17 16:33:59 -04:00
parent 51be90a251
commit 577c05ca1c
1 changed files with 17 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
src/cmd/compile/internal/gc/plive.go
View File

@ -80,8 +80,6 @@ import (
// BlockEffects summarizes the liveness effects on an SSA block.
type BlockEffects struct {
lastbitmapindex int // for Liveness.epilogue
// Computed during Liveness.prologue using only the content of
// individual blocks:
//
@ -988,6 +986,7 @@ func (lv *Liveness) epilogue() {
for _, b := range lv.f.Blocks {
be := lv.blockEffects(b)
firstBitmapIndex := len(lv.livevars)
// Compute avarinitany and avarinitall for entry to block.
// This duplicates information known during Liveness.solve
@ -1039,14 +1038,8 @@ func (lv *Liveness) epilogue() {
lv.livevars = append(lv.livevars, varRegVec{vars: live})
}
be.lastbitmapindex = len(lv.livevars) - 1
}
for _, b := range lv.f.Blocks {
be := lv.blockEffects(b)
// walk backward, construct maps at each safe point
index := int32(be.lastbitmapindex)
index := int32(len(lv.livevars) - 1)
if index < 0 {
// the first block we encounter should have the ATEXT so
// at no point should pos ever be less than zero.
@ -1089,6 +1082,21 @@ func (lv *Liveness) epilogue() {
live := &lv.livevars[index]
live.Or(*live, liveout)
}
// Check that no registers are live across calls.
// For closure calls, the CALLclosure is the last use
// of the context register, so it's dead after the call.
index = int32(firstBitmapIndex)
for _, v := range b.Values {
if lv.issafepoint(v) {
live := lv.livevars[index]
if v.Op.IsCall() && live.regs != 0 {
lv.printDebug()
v.Fatalf("internal error: %v register %s recorded as live at call", lv.fn.Func.Nname, live.regs.niceString(lv.f.Config))
}
index++
}
}
}
// Useful sanity check: on entry to the function,
@ -1107,23 +1115,6 @@ func (lv *Liveness) epilogue() {
lv.printDebug()
lv.f.Fatalf("internal error: %v register %s recorded as live on entry", lv.fn.Func.Nname, regs.niceString(lv.f.Config))
}
// Check that no registers are live across calls.
// For closure calls, the CALLclosure is the last use
// of the context register, so it's dead after the call.
for _, b := range lv.f.Blocks {
index := int32(lv.blockEffects(b).lastbitmapindex)
for i := len(b.Values) - 1; i >= 0; i-- {
v := b.Values[i]
if lv.issafepoint(v) {
live := lv.livevars[index]
if v.Op.IsCall() && live.regs != 0 {
lv.printDebug()
v.Fatalf("internal error: %v register %s recorded as live at call", lv.fn.Func.Nname, live.regs.niceString(lv.f.Config))
}
index--
}
}
}
}
func (lv *Liveness) clobber() {