1 files changed, 63 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/arm64/ssa.go b/src/cmd/compile/internal/arm64/ssa.go
index 52580242dc..24281300ae 100644
--- a/src/cmd/compile/internal/arm64/ssa.go
+++ b/src/cmd/compile/internal/arm64/ssa.go
@@ -182,6 +182,11 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.From.Reg = x
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = y
+	case ssa.OpARM64MOVDnop:
+		if gc.SSARegNum(v) != gc.SSARegNum(v.Args[0]) {
+			v.Fatalf("input[0] and output not in same register %s", v.LongString())
+		}
+		// nothing to do
 	case ssa.OpLoadReg:
 		if v.Type.IsFlags() {
 			v.Unimplementedf("load flags not implemented: %v", v.LongString())
@@ -581,6 +586,64 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 			gc.Maxarg = v.AuxInt
 		}
 	case ssa.OpARM64LoweredNilCheck:
+		// Optimization - if the subsequent block has a load or store
+		// at the same address, we don't need to issue this instruction.
+		mem := v.Args[1]
+		for _, w := range v.Block.Succs[0].Block().Values {
+			if w.Op == ssa.OpPhi {
+				if w.Type.IsMemory() {
+					mem = w
+				}
+				continue
+			}
+			if len(w.Args) == 0 || !w.Args[len(w.Args)-1].Type.IsMemory() {
+				// w doesn't use a store - can't be a memory op.
+				continue
+			}
+			if w.Args[len(w.Args)-1] != mem {
+				v.Fatalf("wrong store after nilcheck v=%s w=%s", v, w)
+			}
+			switch w.Op {
+			case ssa.OpARM64MOVBload, ssa.OpARM64MOVBUload, ssa.OpARM64MOVHload, ssa.OpARM64MOVHUload,
+				ssa.OpARM64MOVWload, ssa.OpARM64MOVWUload, ssa.OpARM64MOVDload,
+				ssa.OpARM64FMOVSload, ssa.OpARM64FMOVDload,
+				ssa.OpARM64MOVBstore, ssa.OpARM64MOVHstore, ssa.OpARM64MOVWstore, ssa.OpARM64MOVDstore,
+				ssa.OpARM64FMOVSstore, ssa.OpARM64FMOVDstore:
+				// arg0 is ptr, auxint is offset
+				if w.Args[0] == v.Args[0] && w.Aux == nil && w.AuxInt >= 0 && w.AuxInt < minZeroPage {
+					if gc.Debug_checknil != 0 && int(v.Line) > 1 {
+						gc.Warnl(v.Line, "removed nil check")
+					}
+					return
+				}
+			case ssa.OpARM64DUFFZERO, ssa.OpARM64LoweredZero:
+				// arg0 is ptr
+				if w.Args[0] == v.Args[0] {
+					if gc.Debug_checknil != 0 && int(v.Line) > 1 {
+						gc.Warnl(v.Line, "removed nil check")
+					}
+					return
+				}
+			case ssa.OpARM64LoweredMove:
+				// arg0 is dst ptr, arg1 is src ptr
+				if w.Args[0] == v.Args[0] || w.Args[1] == v.Args[0] {
+					if gc.Debug_checknil != 0 && int(v.Line) > 1 {
+						gc.Warnl(v.Line, "removed nil check")
+					}
+					return
+				}
+			default:
+			}
+			if w.Type.IsMemory() {
+				if w.Op == ssa.OpVarDef || w.Op == ssa.OpVarKill || w.Op == ssa.OpVarLive {
+					// these ops are OK
+					mem = w
+					continue
+				}
+				// We can't delay the nil check past the next store.
+				break
+			}
+		}
 		// Issue a load which will fault if arg is nil.
 		p := gc.Prog(arm64.AMOVB)
 		p.From.Type = obj.TYPE_MEM