[dev.ssa] cmd/compile/internal/ssa: handle commutative operations in cse

* If a operation is commutative order the parameters
in a canonical way.

Size of pkg/tool/linux_amd64/* excluding compile:
before: 95882288
 after: 95868152
change: 14136 ~0.015%

I tried something similar with Leq and Geq, but the results were
not great because it confuses the 'lowered cse' pass too much
which can no longer remove redundant comparisons from IsInBounds.

Change-Id: I2f928663a11320bfc51c7fa47e384b7411c420ba
Reviewed-on: https://go-review.googlesource.com/19727Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -35,6 +35,10 @@ func cse(f *Func) {
 			if v.Type.IsMemory() {
 				continue // memory values can never cse
 			}
+			if opcodeTable[v.Op].commutative && len(v.Args) == 2 && v.Args[1].ID < v.Args[0].ID {
+				// Order the arguments of binary commutative operations.
+				v.Args[0], v.Args[1] = v.Args[1], v.Args[0]
+			}
 			a = append(a, v)
 		}
 	}

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

@@ -8,10 +8,10 @@ var genericOps = []opData{
 	// 2-input arithmetic
 	// Types must be consistent with Go typing.  Add, for example, must take two values
 	// of the same type and produces that same type.
-	{name: "Add8"}, // arg0 + arg1
-	{name: "Add16"},
-	{name: "Add32"},
-	{name: "Add64"},
+	{name: "Add8", commutative: true}, // arg0 + arg1
+	{name: "Add16", commutative: true},
+	{name: "Add32", commutative: true},
+	{name: "Add64", commutative: true},
 	{name: "AddPtr"}, // For address calculations.  arg0 is a pointer and arg1 is an int.
 	{name: "Add32F"},
 	{name: "Add64F"},
@@ -25,10 +25,10 @@ var genericOps = []opData{
 	{name: "Sub32F"},
 	{name: "Sub64F"},
 
-	{name: "Mul8"}, // arg0 * arg1
-	{name: "Mul16"},
-	{name: "Mul32"},
-	{name: "Mul64"},
+	{name: "Mul8", commutative: true}, // arg0 * arg1
+	{name: "Mul16", commutative: true},
+	{name: "Mul32", commutative: true},
+	{name: "Mul64", commutative: true},
 	{name: "Mul32F"},
 	{name: "Mul64F"},
 
@@ -65,20 +65,20 @@ var genericOps = []opData{
 	{name: "Mod64"},
 	{name: "Mod64u"},
 
-	{name: "And8"}, // arg0 & arg1
-	{name: "And16"},
-	{name: "And32"},
-	{name: "And64"},
+	{name: "And8", commutative: true}, // arg0 & arg1
+	{name: "And16", commutative: true},
+	{name: "And32", commutative: true},
+	{name: "And64", commutative: true},
 
-	{name: "Or8"}, // arg0 | arg1
-	{name: "Or16"},
-	{name: "Or32"},
-	{name: "Or64"},
+	{name: "Or8", commutative: true}, // arg0 | arg1
+	{name: "Or16", commutative: true},
+	{name: "Or32", commutative: true},
+	{name: "Or64", commutative: true},
 
-	{name: "Xor8"}, // arg0 ^ arg1
-	{name: "Xor16"},
-	{name: "Xor32"},
-	{name: "Xor64"},
+	{name: "Xor8", commutative: true}, // arg0 ^ arg1
+	{name: "Xor16", commutative: true},
+	{name: "Xor32", commutative: true},
+	{name: "Xor64", commutative: true},
 
 	// For shifts, AxB means the shifted value has A bits and the shift amount has B bits.
 	{name: "Lsh8x8"}, // arg0 << arg1
@@ -158,21 +158,21 @@ var genericOps = []opData{
 	{name: "Lrot64", aux: "Int64"},
 
 	// 2-input comparisons
-	{name: "Eq8"}, // arg0 == arg1
-	{name: "Eq16"},
-	{name: "Eq32"},
-	{name: "Eq64"},
-	{name: "EqPtr"},
+	{name: "Eq8", commutative: true}, // arg0 == arg1
+	{name: "Eq16", commutative: true},
+	{name: "Eq32", commutative: true},
+	{name: "Eq64", commutative: true},
+	{name: "EqPtr", commutative: true},
 	{name: "EqInter"}, // arg0 or arg1 is nil; other cases handled by frontend
 	{name: "EqSlice"}, // arg0 or arg1 is nil; other cases handled by frontend
 	{name: "Eq32F"},
 	{name: "Eq64F"},
 
-	{name: "Neq8"}, // arg0 != arg1
-	{name: "Neq16"},
-	{name: "Neq32"},
-	{name: "Neq64"},
-	{name: "NeqPtr"},
+	{name: "Neq8", commutative: true}, // arg0 != arg1
+	{name: "Neq16", commutative: true},
+	{name: "Neq32", commutative: true},
+	{name: "Neq64", commutative: true},
+	{name: "NeqPtr", commutative: true},
 	{name: "NeqInter"}, // arg0 or arg1 is nil; other cases handled by frontend
 	{name: "NeqSlice"}, // arg0 or arg1 is nil; other cases handled by frontend
 	{name: "Neq32F"},

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

@@ -32,7 +32,8 @@ type opData struct {
 	typ               string // default result type
 	aux               string
 	rematerializeable bool
-	variableLength    bool // if true the operation has a variable number of arguments
+	variableLength    bool // this operation has a variable number of arguments
+	commutative       bool // this operation is commutative (e.g. addition)
 }
 
 type blockData struct {
@@ -131,6 +132,9 @@ func genOp() {
 				}
 				fmt.Fprintln(w, "rematerializeable: true,")
 			}
+			if v.commutative {
+				fmt.Fprintln(w, "commutative: true,")
+			}
 			if a.name == "generic" {
 				fmt.Fprintln(w, "generic:true,")
 				fmt.Fprintln(w, "},") // close op

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

@@ -21,6 +21,7 @@ type opInfo struct {
 	auxType           auxType
 	generic           bool // this is a generic (arch-independent) opcode
 	rematerializeable bool // this op is rematerializeable
+	commutative       bool // this operation is commutative (e.g. addition)
 }
 
 type inputInfo struct {

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

@@ -3597,20 +3597,24 @@ var opcodeTable = [...]opInfo{
 	},
 
 	{
-		name:    "Add8",
-		generic: true,
+		name:        "Add8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Add16",
-		generic: true,
+		name:        "Add16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Add32",
-		generic: true,
+		name:        "Add32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Add64",
-		generic: true,
+		name:        "Add64",
+		commutative: true,
+		generic:     true,
 	},
 	{
 		name:    "AddPtr",
@@ -3653,20 +3657,24 @@ var opcodeTable = [...]opInfo{
 		generic: true,
 	},
 	{
-		name:    "Mul8",
-		generic: true,
+		name:        "Mul8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Mul16",
-		generic: true,
+		name:        "Mul16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Mul32",
-		generic: true,
+		name:        "Mul32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Mul64",
-		generic: true,
+		name:        "Mul64",
+		commutative: true,
+		generic:     true,
 	},
 	{
 		name:    "Mul32F",
@@ -3785,52 +3793,64 @@ var opcodeTable = [...]opInfo{
 		generic: true,
 	},
 	{
-		name:    "And8",
-		generic: true,
+		name:        "And8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "And16",
-		generic: true,
+		name:        "And16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "And32",
-		generic: true,
+		name:        "And32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "And64",
-		generic: true,
+		name:        "And64",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Or8",
-		generic: true,
+		name:        "Or8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Or16",
-		generic: true,
+		name:        "Or16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Or32",
-		generic: true,
+		name:        "Or32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Or64",
-		generic: true,
+		name:        "Or64",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Xor8",
-		generic: true,
+		name:        "Xor8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Xor16",
-		generic: true,
+		name:        "Xor16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Xor32",
-		generic: true,
+		name:        "Xor32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Xor64",
-		generic: true,
+		name:        "Xor64",
+		commutative: true,
+		generic:     true,
 	},
 	{
 		name:    "Lsh8x8",
@@ -4045,24 +4065,29 @@ var opcodeTable = [...]opInfo{
 		generic: true,
 	},
 	{
-		name:    "Eq8",
-		generic: true,
+		name:        "Eq8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Eq16",
-		generic: true,
+		name:        "Eq16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Eq32",
-		generic: true,
+		name:        "Eq32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Eq64",
-		generic: true,
+		name:        "Eq64",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "EqPtr",
-		generic: true,
+		name:        "EqPtr",
+		commutative: true,
+		generic:     true,
 	},
 	{
 		name:    "EqInter",
@@ -4081,24 +4106,29 @@ var opcodeTable = [...]opInfo{
 		generic: true,
 	},
 	{
-		name:    "Neq8",
-		generic: true,
+		name:        "Neq8",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Neq16",
-		generic: true,
+		name:        "Neq16",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Neq32",
-		generic: true,
+		name:        "Neq32",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "Neq64",
-		generic: true,
+		name:        "Neq64",
+		commutative: true,
+		generic:     true,
 	},
 	{
-		name:    "NeqPtr",
-		generic: true,
+		name:        "NeqPtr",
+		commutative: true,
+		generic:     true,
 	},
 	{
 		name:    "NeqInter",