[dev.ssa] cmd/compile/internal/ssa: replace load of store with a copy

This is a AMD64 version of CL19743.
Saves additional 1574 bytes in go binary.
This also speeds up bzip2 by 1-4%

Change-Id: I031ba423663c4e83fdefe44e5296f24143e303da
Reviewed-on: https://go-review.googlesource.com/19939
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -608,6 +608,12 @@
 (MOVLQSX (MOVLload [off] {sym} ptr mem)) -> @v.Args[0].Block (MOVLQSXload <v.Type> [off] {sym} ptr mem)
 (MOVLQZX (MOVLload [off] {sym} ptr mem)) -> @v.Args[0].Block (MOVLQZXload <v.Type> [off] {sym} ptr mem)
 
+// replace load from same location as preceding store with copy
+(MOVBload [off] {sym} ptr (MOVBstore [off2] {sym2} ptr2 x _)) && sym == sym2 && off == off2 && isSamePtr(ptr, ptr2) -> x
+(MOVWload [off] {sym} ptr (MOVWstore [off2] {sym2} ptr2 x _)) && sym == sym2 && off == off2 && isSamePtr(ptr, ptr2) -> x
+(MOVLload [off] {sym} ptr (MOVLstore [off2] {sym2} ptr2 x _)) && sym == sym2 && off == off2 && isSamePtr(ptr, ptr2) -> x
+(MOVQload [off] {sym} ptr (MOVQstore [off2] {sym2} ptr2 x _)) && sym == sym2 && off == off2 && isSamePtr(ptr, ptr2) -> x
+
 // Fold extensions and ANDs together.
 (MOVBQZX (ANDBconst [c] x)) -> (ANDQconst [c & 0xff] x)
 (MOVWQZX (ANDWconst [c] x)) -> (ANDQconst [c & 0xffff] x)

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -5459,6 +5459,28 @@ func rewriteValueAMD64_OpAMD64MOVBQZX(v *Value, config *Config) bool {
 func rewriteValueAMD64_OpAMD64MOVBload(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (MOVBload [off] {sym} ptr (MOVBstore [off2] {sym2} ptr2 x _))
+	// cond: sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)
+	// result: x
+	for {
+		off := v.AuxInt
+		sym := v.Aux
+		ptr := v.Args[0]
+		if v.Args[1].Op != OpAMD64MOVBstore {
+			break
+		}
+		off2 := v.Args[1].AuxInt
+		sym2 := v.Args[1].Aux
+		ptr2 := v.Args[1].Args[0]
+		x := v.Args[1].Args[1]
+		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
+			break
+		}
+		v.reset(OpCopy)
+		v.Type = x.Type
+		v.AddArg(x)
+		return true
+	}
 	// match: (MOVBload  [off1] {sym} (ADDQconst [off2] ptr) mem)
 	// cond:
 	// result: (MOVBload  [addOff(off1, off2)] {sym} ptr mem)
@@ -6042,6 +6064,28 @@ func rewriteValueAMD64_OpAMD64MOVLQZX(v *Value, config *Config) bool {
 func rewriteValueAMD64_OpAMD64MOVLload(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (MOVLload [off] {sym} ptr (MOVLstore [off2] {sym2} ptr2 x _))
+	// cond: sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)
+	// result: x
+	for {
+		off := v.AuxInt
+		sym := v.Aux
+		ptr := v.Args[0]
+		if v.Args[1].Op != OpAMD64MOVLstore {
+			break
+		}
+		off2 := v.Args[1].AuxInt
+		sym2 := v.Args[1].Aux
+		ptr2 := v.Args[1].Args[0]
+		x := v.Args[1].Args[1]
+		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
+			break
+		}
+		v.reset(OpCopy)
+		v.Type = x.Type
+		v.AddArg(x)
+		return true
+	}
 	// match: (MOVLload  [off1] {sym} (ADDQconst [off2] ptr) mem)
 	// cond:
 	// result: (MOVLload  [addOff(off1, off2)] {sym} ptr mem)
@@ -6572,6 +6616,28 @@ func rewriteValueAMD64_OpAMD64MOVOstore(v *Value, config *Config) bool {
 func rewriteValueAMD64_OpAMD64MOVQload(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (MOVQload [off] {sym} ptr (MOVQstore [off2] {sym2} ptr2 x _))
+	// cond: sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)
+	// result: x
+	for {
+		off := v.AuxInt
+		sym := v.Aux
+		ptr := v.Args[0]
+		if v.Args[1].Op != OpAMD64MOVQstore {
+			break
+		}
+		off2 := v.Args[1].AuxInt
+		sym2 := v.Args[1].Aux
+		ptr2 := v.Args[1].Args[0]
+		x := v.Args[1].Args[1]
+		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
+			break
+		}
+		v.reset(OpCopy)
+		v.Type = x.Type
+		v.AddArg(x)
+		return true
+	}
 	// match: (MOVQload  [off1] {sym} (ADDQconst [off2] ptr) mem)
 	// cond:
 	// result: (MOVQload  [addOff(off1, off2)] {sym} ptr mem)
@@ -7543,6 +7609,28 @@ func rewriteValueAMD64_OpAMD64MOVWQZX(v *Value, config *Config) bool {
 func rewriteValueAMD64_OpAMD64MOVWload(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (MOVWload [off] {sym} ptr (MOVWstore [off2] {sym2} ptr2 x _))
+	// cond: sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)
+	// result: x
+	for {
+		off := v.AuxInt
+		sym := v.Aux
+		ptr := v.Args[0]
+		if v.Args[1].Op != OpAMD64MOVWstore {
+			break
+		}
+		off2 := v.Args[1].AuxInt
+		sym2 := v.Args[1].Aux
+		ptr2 := v.Args[1].Args[0]
+		x := v.Args[1].Args[1]
+		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
+			break
+		}
+		v.reset(OpCopy)
+		v.Type = x.Type
+		v.AddArg(x)
+		return true
+	}
 	// match: (MOVWload  [off1] {sym} (ADDQconst [off2] ptr) mem)
 	// cond:
 	// result: (MOVWload  [addOff(off1, off2)] {sym} ptr mem)