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[dev.ssa] cmd/compile: assign unused registers to phi ops
Register phis are better than stack phis. If we have unused registers available, use them for phis. Change-Id: I3045711c65caa1b6d0be29131b87b57466320cc2 Reviewed-on: https://go-review.googlesource.com/16080 Run-TryBot: Keith Randall <khr@golang.org> Reviewed-by: David Chase <drchase@google.com>
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@ -567,14 +567,12 @@ func (s *regAllocState) setState(state []regState) {
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}
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}
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// compatReg returns a register compatible with the a value and is used when
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// spilling/loading.
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// TODO: choose a better default register (set of reg by type?).
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func compatReg(v *Value) regMask {
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// compatRegs returns the set of registers which can store v.
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func (v *Value) compatRegs() regMask {
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if v.Type.IsFloat() {
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return 1 << 16 // X0
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return 0xffff << 16 // X0-X15
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}
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return 1 << 0 // AX
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return 0xffef << 0 // AX-R15, except SP
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}
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func (s *regAllocState) regalloc(f *Func) {
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@ -688,15 +686,21 @@ func (s *regAllocState) regalloc(f *Func) {
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}
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r := phiRegs[i]
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if r == noRegister {
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// stack-based phi
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// Spills will be inserted in all the predecessors below.
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s.values[v.ID].spill = v // v starts life spilled
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s.values[v.ID].spillUsed = true // use is guaranteed
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continue
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m := v.compatRegs() & ^s.used
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if m == 0 {
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// stack-based phi
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// Spills will be inserted in all the predecessors below.
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s.values[v.ID].spill = v // v starts life spilled
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s.values[v.ID].spillUsed = true // use is guaranteed
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continue
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}
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// Allocate phi to an unused register.
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r = pickReg(m)
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} else {
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s.freeReg(r)
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}
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// register-based phi
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// Transfer ownership of register from input arg to phi.
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s.freeReg(r)
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s.assignReg(r, v, v)
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// Spill the phi in case we need to restore it later.
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spill := b.NewValue1(v.Line, OpStoreReg, v.Type, v)
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@ -872,7 +876,7 @@ func (s *regAllocState) regalloc(f *Func) {
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// This stack-based phi is the argument of some other
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// phi in this block. We must make a copy of its
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// value so that we don't clobber it prematurely.
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c := s.allocValToReg(v, s.values[v.ID].regs|compatReg(v), false)
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c := s.allocValToReg(v, v.compatRegs(), false)
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d := p.NewValue1(v.Line, OpStoreReg, v.Type, c)
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s.values[v.ID].spill2 = d
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}
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@ -884,7 +888,7 @@ func (s *regAllocState) regalloc(f *Func) {
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// If already in a register, use that. If not, pick a compatible
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// register.
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w := v.Args[i]
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c := s.allocValToReg(w, s.values[w.ID].regs|compatReg(w), false)
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c := s.allocValToReg(w, w.compatRegs(), false)
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v.Args[i] = p.NewValue1(v.Line, OpStoreReg, v.Type, c)
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}
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// Figure out what value goes in each register.
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