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cmd/compile: place reg spills after OpArg{Int,Float}Reg ops

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Tweak the register allocator to maintain the invariant that
OpArg{Int,Float}Reg values are placed together at the start of the
entry block, before any other non-pseudo-op values. Without this
change, when the register allocator adds spills we can wind up with an
interleaving of OpArg*Reg and stores, which complicates debug location
analysis.

Updates #40724.

Change-Id: Icf30dd814a9e25263ecbea2e48feb840a6e7f2bd
Reviewed-on: https://go-review.googlesource.com/c/go/+/322630
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Than McIntosh 2021-05-25 10:13:07 -04:00
parent db66e9e15d
commit 56af34f875
1 changed files with 10 additions and 6 deletions
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16
src/cmd/compile/internal/ssa/regalloc.go
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@ -1882,6 +1882,10 @@ func (s *regAllocState) placeSpills() {
phiRegs[b.ID] = m
}
mustBeFirst := func(op Op) bool {
return op.isLoweredGetClosurePtr() || op == OpPhi || op == OpArgIntReg || op == OpArgFloatReg
}
// Start maps block IDs to the list of spills
// that go at the start of the block (but after any phis).
start := map[ID][]*Value{}
@ -1971,7 +1975,7 @@ func (s *regAllocState) placeSpills() {
// Put the spill in the best block we found.
spill.Block = best
spill.AddArg(bestArg)
if best == v.Block && v.Op != OpPhi {
if best == v.Block && !mustBeFirst(v.Op) {
// Place immediately after v.
after[v.ID] = append(after[v.ID], spill)
} else {
@ -1983,15 +1987,15 @@ func (s *regAllocState) placeSpills() {
// Insert spill instructions into the block schedules.
var oldSched []*Value
for _, b := range s.visitOrder {
nphi := 0
nfirst := 0
for _, v := range b.Values {
if v.Op != OpPhi {
if !mustBeFirst(v.Op) {
break
}
nphi++
nfirst++
}
oldSched = append(oldSched[:0], b.Values[nphi:]...)
b.Values = b.Values[:nphi]
oldSched = append(oldSched[:0], b.Values[nfirst:]...)
b.Values = b.Values[:nfirst]
b.Values = append(b.Values, start[b.ID]...)
for _, v := range oldSched {
b.Values = append(b.Values, v)