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

Loads of stores from the same pointer with compatible types
can be replaced with a copy.

Change-Id: I514b3ed8e5b6a9c432946880eac67a51b1607932
Reviewed-on: https://go-review.googlesource.com/19743
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/ssa/gen/generic.rules b/src/cmd/compile/internal/ssa/gen/generic.rules
index f83634c3943431af19a50d002c4a473c7554ea6d..4d4310555731673fc48fc6698984e2940aaf84c7 100644 (file)
--- a/src/cmd/compile/internal/ssa/gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/gen/generic.rules
@@ -388,6 +388,11 @@
 (EqSlice x y)  -> (EqPtr  (SlicePtr x) (SlicePtr y))
 (NeqSlice x y) -> (NeqPtr (SlicePtr x) (SlicePtr y))
 
+
+// Load of store of same address, with compatibly typed value and same size
+(Load <t1> p1 (Store [w] p2 x _)) && isSamePtr(p1,p2) && t1.Compare(x.Type)==CMPeq && w == t1.Size() -> x
+
+
 // indexing operations
 // Note: bounds check has already been done
 (ArrayIndex (Load ptr mem) idx) && b == v.Args[0].Block -> (Load (PtrIndex <v.Type.PtrTo()> ptr idx) mem)

diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index a580945702e910189c506e1888eac84daea7b8c2..4197b0da8846f22d23c8376228c6bfb026c1a453 100644 (file)
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -202,6 +202,15 @@ func uaddOvf(a, b int64) bool {
        return uint64(a)+uint64(b) < uint64(a)
 }
 
+// isSamePtr reports whether p1 and p2 point to the same address.
+func isSamePtr(p1, p2 *Value) bool {
+       // Aux isn't used  in OffPtr, and AuxInt isn't currently used in
+       // Addr, but this still works as the values will be null/0
+       return (p1.Op == OpOffPtr || p1.Op == OpAddr) && p1.Op == p2.Op &&
+               p1.Aux == p2.Aux && p1.AuxInt == p2.AuxInt &&
+               p1.Args[0] == p2.Args[0]
+}
+
 // DUFFZERO consists of repeated blocks of 4 MOVUPSs + ADD,
 // See runtime/mkduff.go.
 const (

diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index ae36112a508a85918f6e8b16153dd32aa6e6197c..7916c6d8f412caac23a48853be15bac0a0a1616f 100644 (file)
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -2901,6 +2901,26 @@ func rewriteValuegeneric_OpLess8U(v *Value, config *Config) bool {
 func rewriteValuegeneric_OpLoad(v *Value, config *Config) bool {
        b := v.Block
        _ = b
+       // match: (Load <t1> p1 (Store [w] p2 x _))
+       // cond: isSamePtr(p1,p2) && t1.Compare(x.Type)==CMPeq && w == t1.Size()
+       // result: x
+       for {
+               t1 := v.Type
+               p1 := v.Args[0]
+               if v.Args[1].Op != OpStore {
+                       break
+               }
+               w := v.Args[1].AuxInt
+               p2 := v.Args[1].Args[0]
+               x := v.Args[1].Args[1]
+               if !(isSamePtr(p1, p2) && t1.Compare(x.Type) == CMPeq && w == t1.Size()) {
+                       break
+               }
+               v.reset(OpCopy)
+               v.Type = x.Type
+               v.AddArg(x)
+               return true
+       }
        // match: (Load <t> _ _)
        // cond: t.IsStruct() && t.NumFields() == 0 && config.fe.CanSSA(t)
        // result: (StructMake0)