[dev.ssa] cmd/compile: add a zero arg cse pass

Add an initial cse pass that only operates on zero argument
values.  This removes the need for a special case in cse for removing
OpSB and speeds up arithConst_ssa.go compilation by 9% while slowing
"test -c net/http" by 1.5%.

Change-Id: Id1500482485426f66c6c2eba75eeaf4f19c8a889
Reviewed-on: https://go-review.googlesource.com/19454
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -102,8 +102,9 @@ var passes = [...]pass{
 	{"decompose user", decomposeUser, true},
 	{"decompose builtin", decomposeBuiltIn, true},
 	{"opt", opt, true},                // TODO: split required rules and optimizing rules
+	{"zero arg cse", zcse, true},      // required to merge OpSB values
 	{"opt deadcode", deadcode, false}, // remove any blocks orphaned during opt
-	{"generic cse", cse, true},
+	{"generic cse", cse, false},
 	{"nilcheckelim", nilcheckelim, false},
 	{"generic deadcode", deadcode, false},
 	{"fuse", fuse, false},

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

@@ -13,34 +13,6 @@ import (
 // Values are just relinked, nothing is deleted.  A subsequent deadcode
 // pass is required to actually remove duplicate expressions.
 func cse(f *Func) {
-	if !f.Config.optimize {
-		// Don't do CSE in this case.  But we need to do
-		// just a little bit, to combine multiple OpSB ops.
-		// Regalloc gets very confused otherwise.
-		var sb *Value
-	outer:
-		for _, b := range f.Blocks {
-			for _, v := range b.Values {
-				if v.Op == OpSB {
-					sb = v
-					break outer
-				}
-			}
-		}
-		if sb == nil {
-			return
-		}
-		for _, b := range f.Blocks {
-			for _, v := range b.Values {
-				for i, a := range v.Args {
-					if a.Op == OpSB {
-						v.Args[i] = sb
-					}
-				}
-			}
-		}
-		return
-	}
 	// Two values are equivalent if they satisfy the following definition:
 	// equivalent(v, w):
 	//   v.op == w.op
@@ -77,6 +49,14 @@ func cse(f *Func) {
 		}
 	}
 	for i, e := range partition {
+		if Debug > 1 && len(e) > 500 {
+			fmt.Printf("CSE.large partition (%d): ", len(e))
+			for j := 0; j < 3; j++ {
+				fmt.Printf("%s ", e[j].LongString())
+			}
+			fmt.Println()
+		}
+
 		for _, v := range e {
 			valueEqClass[v.ID] = ID(i)
 		}

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

@@ -6,12 +6,16 @@ package ssa
 
 import "testing"
 
+type tstAux struct {
+	s string
+}
+
 // This tests for a bug found when partitioning, but not sorting by the Aux value.
 func TestCSEAuxPartitionBug(t *testing.T) {
 	c := testConfig(t)
-	arg1Aux := "arg1-aux"
-	arg2Aux := "arg2-aux"
-	arg3Aux := "arg3-aux"
+	arg1Aux := &tstAux{"arg1-aux"}
+	arg2Aux := &tstAux{"arg2-aux"}
+	arg3Aux := &tstAux{"arg3-aux"}
 
 	// construct lots of values with args that have aux values and place
 	// them in an order that triggers the bug
@@ -77,5 +81,43 @@ func TestCSEAuxPartitionBug(t *testing.T) {
 	if s1Cnt != 0 || s2Cnt != 0 {
 		t.Errorf("%d values missed during cse", s1Cnt+s2Cnt)
 	}
+}
 
+// TestZCSE tests the zero arg cse.
+func TestZCSE(t *testing.T) {
+	c := testConfig(t)
+
+	fun := Fun(c, "entry",
+		Bloc("entry",
+			Valu("start", OpInitMem, TypeMem, 0, nil),
+			Valu("sp", OpSP, TypeBytePtr, 0, nil),
+			Valu("sb1", OpSB, TypeBytePtr, 0, nil),
+			Valu("sb2", OpSB, TypeBytePtr, 0, nil),
+			Valu("addr1", OpAddr, TypeInt64Ptr, 0, nil, "sb1"),
+			Valu("addr2", OpAddr, TypeInt64Ptr, 0, nil, "sb2"),
+			Valu("a1ld", OpLoad, TypeInt64, 0, nil, "addr1", "start"),
+			Valu("a2ld", OpLoad, TypeInt64, 0, nil, "addr2", "start"),
+			Valu("c1", OpConst64, TypeInt64, 1, nil),
+			Valu("r1", OpAdd64, TypeInt64, 0, nil, "a1ld", "c1"),
+			Valu("c2", OpConst64, TypeInt64, 1, nil),
+			Valu("r2", OpAdd64, TypeInt64, 0, nil, "a2ld", "c2"),
+			Valu("r3", OpAdd64, TypeInt64, 0, nil, "r1", "r2"),
+			Valu("raddr", OpAddr, TypeInt64Ptr, 0, nil, "sp"),
+			Valu("raddrdef", OpVarDef, TypeMem, 0, nil, "start"),
+			Valu("rstore", OpStore, TypeMem, 8, nil, "raddr", "r3", "raddrdef"),
+			Goto("exit")),
+		Bloc("exit",
+			Exit("rstore")))
+
+	CheckFunc(fun.f)
+	zcse(fun.f)
+	deadcode(fun.f)
+	CheckFunc(fun.f)
+
+	if fun.values["c1"].Op != OpInvalid && fun.values["c2"].Op != OpInvalid {
+		t.Errorf("zsce should have removed c1 or c2")
+	}
+	if fun.values["sb1"].Op != OpInvalid && fun.values["sb2"].Op != OpInvalid {
+		t.Errorf("zsce should have removed sb1 or sb2")
+	}
 }

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

+// Copyright 2016 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
+
+// zcse does an initial pass of common-subexpression elimination on the
+// function for values with zero arguments to allow the more expensive cse
+// to begin with a reduced number of values. Values are just relinked,
+// nothing is deleted. A subsequent deadcode pass is required to actually
+// remove duplicate expressions.
+func zcse(f *Func) {
+	vals := make(map[vkey]*Value)
+
+	for _, b := range f.Blocks {
+		for i := 0; i < len(b.Values); {
+			v := b.Values[i]
+			next := true
+			switch v.Op {
+			case OpSB, OpConst64, OpConst32, OpConst16, OpConst8, OpConst64F,
+				OpConst32F, OpConstBool, OpConstNil, OpConstSlice, OpConstInterface:
+				key := vkey{v.Op, keyFor(v), typeStr(v)}
+				if vals[key] == nil {
+					vals[key] = v
+					if b != f.Entry {
+						// Move v to the entry block so it will dominate every block
+						// where we might use it. This prevents the need for any dominator
+						// calculations in this pass.
+						v.Block = f.Entry
+						f.Entry.Values = append(f.Entry.Values, v)
+						last := len(b.Values) - 1
+						b.Values[i] = b.Values[last]
+						b.Values[last] = nil
+						b.Values = b.Values[:last]
+
+						// process b.Values[i] again
+						next = false
+					}
+				}
+			}
+			if next {
+				i++
+			}
+		}
+	}
+
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			for i, a := range v.Args {
+				// TODO: encode arglen in the opcode table, then do this switch with a table lookup?
+				switch a.Op {
+				case OpSB, OpConst64, OpConst32, OpConst16, OpConst8, OpConst64F,
+					OpConst32F, OpConstBool, OpConstNil, OpConstSlice, OpConstInterface:
+					key := vkey{a.Op, keyFor(a), typeStr(a)}
+					if rv, ok := vals[key]; ok {
+						v.Args[i] = rv
+					}
+				}
+			}
+		}
+	}
+}
+
+// vkey is a type used to uniquely identify a zero arg value.
+type vkey struct {
+	op Op
+	a  int64  // aux
+	t  string // type
+}
+
+// typeStr returns a string version of the type of v.
+func typeStr(v *Value) string {
+	if v.Type == nil {
+		return ""
+	}
+	return v.Type.String()
+}
+
+// keyFor returns the AuxInt portion of a  key structure uniquely identifying a
+// zero arg value for the supported ops.
+func keyFor(v *Value) int64 {
+	switch v.Op {
+	case OpConst64, OpConst64F, OpConst32F:
+		return v.AuxInt
+	case OpConst32:
+		return int64(int32(v.AuxInt))
+	case OpConst16:
+		return int64(int16(v.AuxInt))
+	case OpConst8, OpConstBool:
+		return int64(int8(v.AuxInt))
+	default:
+		// Also matches OpSB, OpConstNil, OpConstSlice, OpConstInterface:
+		return 0
+	}
+}