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cmd/compile: place reg spills after OpArg{Int,Float}Reg ops
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>
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@ -1882,6 +1882,10 @@ func (s *regAllocState) placeSpills() {
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phiRegs[b.ID] = m
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}
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mustBeFirst := func(op Op) bool {
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return op.isLoweredGetClosurePtr() || op == OpPhi || op == OpArgIntReg || op == OpArgFloatReg
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}
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// Start maps block IDs to the list of spills
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// that go at the start of the block (but after any phis).
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start := map[ID][]*Value{}
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@ -1971,7 +1975,7 @@ func (s *regAllocState) placeSpills() {
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// Put the spill in the best block we found.
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spill.Block = best
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spill.AddArg(bestArg)
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if best == v.Block && v.Op != OpPhi {
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if best == v.Block && !mustBeFirst(v.Op) {
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// Place immediately after v.
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after[v.ID] = append(after[v.ID], spill)
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} else {
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@ -1983,15 +1987,15 @@ func (s *regAllocState) placeSpills() {
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// Insert spill instructions into the block schedules.
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var oldSched []*Value
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for _, b := range s.visitOrder {
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nphi := 0
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nfirst := 0
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for _, v := range b.Values {
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if v.Op != OpPhi {
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if !mustBeFirst(v.Op) {
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break
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}
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nphi++
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nfirst++
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}
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oldSched = append(oldSched[:0], b.Values[nphi:]...)
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b.Values = b.Values[:nphi]
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oldSched = append(oldSched[:0], b.Values[nfirst:]...)
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b.Values = b.Values[:nfirst]
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b.Values = append(b.Values, start[b.ID]...)
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for _, v := range oldSched {
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b.Values = append(b.Values, v)
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