[dev.ssa] cmd/internal/ssa: add deadstore pass
Eliminate dead stores. Dead stores are those which are
unconditionally followed by another store to the same location, with
no intervening load.
Just a simple intra-block implementation for now.
Change-Id: I2bf54e3a342608fc4e01edbe1b429e83f24764ab
Reviewed-on: https://go-review.googlesource.com/10386
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
diff --git a/src/cmd/compile/internal/ssa/deadstore_test.go b/src/cmd/compile/internal/ssa/deadstore_test.go
new file mode 100644
index 0000000..70b2092
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/deadstore_test.go
@@ -0,0 +1,87 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ssa
+
+import (
+ "testing"
+)
+
+func TestDeadStore(t *testing.T) {
+ c := NewConfig("amd64", DummyFrontend{})
+ ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
+ fun := Fun(c, "entry",
+ Bloc("entry",
+ Valu("start", OpArg, TypeMem, ".mem"),
+ Valu("v", OpConst, TypeBool, true),
+ Valu("addr1", OpGlobal, ptrType, nil),
+ Valu("addr2", OpGlobal, ptrType, nil),
+ Valu("store1", OpStore, TypeMem, nil, "addr1", "v", "start"),
+ Valu("store2", OpStore, TypeMem, nil, "addr2", "v", "store1"),
+ Valu("store3", OpStore, TypeMem, nil, "addr1", "v", "store2"),
+ Goto("exit")),
+ Bloc("exit",
+ Exit("store3")))
+
+ CheckFunc(fun.f)
+ dse(fun.f)
+ CheckFunc(fun.f)
+
+ v := fun.values["store1"]
+ if v.Op != OpCopy {
+ t.Errorf("dead store not removed")
+ }
+}
+func TestDeadStorePhi(t *testing.T) {
+ // make sure we don't get into an infinite loop with phi values.
+ c := NewConfig("amd64", DummyFrontend{})
+ ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
+ fun := Fun(c, "entry",
+ Bloc("entry",
+ Valu("start", OpArg, TypeMem, ".mem"),
+ Valu("v", OpConst, TypeBool, true),
+ Valu("addr", OpGlobal, ptrType, nil),
+ Goto("loop")),
+ Bloc("loop",
+ Valu("phi", OpPhi, TypeMem, nil, "start", "store"),
+ Valu("store", OpStore, TypeMem, nil, "addr", "v", "phi"),
+ If("v", "loop", "exit")),
+ Bloc("exit",
+ Exit("store")))
+
+ CheckFunc(fun.f)
+ dse(fun.f)
+ CheckFunc(fun.f)
+}
+
+func TestDeadStoreTypes(t *testing.T) {
+ // Make sure a narrow store can't shadow a wider one. We test an even
+ // stronger restriction, that one store can't shadow another unless the
+ // types of the address fields are identical (where identicalness is
+ // decided by the CSE pass).
+ c := NewConfig("amd64", DummyFrontend{})
+ t1 := &TypeImpl{Size_: 8, Ptr: true, Name: "t1"}
+ t2 := &TypeImpl{Size_: 4, Ptr: true, Name: "t2"}
+ fun := Fun(c, "entry",
+ Bloc("entry",
+ Valu("start", OpArg, TypeMem, ".mem"),
+ Valu("v", OpConst, TypeBool, true),
+ Valu("addr1", OpGlobal, t1, nil),
+ Valu("addr2", OpGlobal, t2, nil),
+ Valu("store1", OpStore, TypeMem, nil, "addr1", "v", "start"),
+ Valu("store2", OpStore, TypeMem, nil, "addr2", "v", "store1"),
+ Goto("exit")),
+ Bloc("exit",
+ Exit("store2")))
+
+ CheckFunc(fun.f)
+ cse(fun.f)
+ dse(fun.f)
+ CheckFunc(fun.f)
+
+ v := fun.values["store1"]
+ if v.Op == OpCopy {
+ t.Errorf("store %s incorrectly removed", v)
+ }
+}
