cmd/compile: fold negation into addition/subtraction on mipsx

Fold negation into addition/subtraction and avoid double negation.

file      before    after     Δ       %
addr2line 3742022   3741986   -36     -0.001%
asm       6668616   6668628   +12     +0.000%
buildid   3583786   3583630   -156    -0.004%
cgo       6020370   6019634   -736    -0.012%
compile   29416016  29417336  +1320   +0.004%
cover     6801903   6801675   -228    -0.003%
dist      4485916   4485816   -100    -0.002%
doc       10652787  10652251  -536    -0.005%
fix       4115988   4115560   -428    -0.010%
link      9002328   9001616   -712    -0.008%
nm        3733148   3732780   -368    -0.010%
objdump   6163292   6163068   -224    -0.004%
pack      2944768   2944604   -164    -0.006%
pprof     18909973  18908773  -1200   -0.006%
test2json 3394662   3394778   +116    +0.003%
trace     17350911  17349751  -1160   -0.007%
vet       10077727  10077527  -200    -0.002%
go        19118769  19118609  -160    -0.001%
total     166182982 166178022 -4960   -0.003%

Change-Id: Id55698800fd70f3cb2ff48393584456b87208921
Reviewed-on: https://go-review.googlesource.com/c/go/+/673556
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/cmd/compile/internal/ssa/_gen/MIPS.rules

@@ -614,11 +614,14 @@
 
 // generic simplifications
 (ADD x (NEG y)) => (SUB x y)
+(SUB x (NEG y)) => (ADD x y)
 (SUB x x) => (MOVWconst [0])
 (SUB (MOVWconst [0]) x) => (NEG x)
 (AND x x) => x
 (OR  x x) => x
 (XOR x x) => (MOVWconst [0])
+(NEG (SUB x y)) => (SUB y x)
+(NEG (NEG x)) => x
 
 // miscellaneous patterns generated by dec64
 (AND (SGTUconst [1] x) (SGTUconst [1] y)) =>  (SGTUconst [1] (OR <x.Type> x y))

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

@@ -4096,6 +4096,28 @@ func rewriteValueMIPS_OpMIPSMUL(v *Value) bool {
 }
 func rewriteValueMIPS_OpMIPSNEG(v *Value) bool {
 	v_0 := v.Args[0]
+	// match: (NEG (SUB x y))
+	// result: (SUB y x)
+	for {
+		if v_0.Op != OpMIPSSUB {
+			break
+		}
+		y := v_0.Args[1]
+		x := v_0.Args[0]
+		v.reset(OpMIPSSUB)
+		v.AddArg2(y, x)
+		return true
+	}
+	// match: (NEG (NEG x))
+	// result: x
+	for {
+		if v_0.Op != OpMIPSNEG {
+			break
+		}
+		x := v_0.Args[0]
+		v.copyOf(x)
+		return true
+	}
 	// match: (NEG (MOVWconst [c]))
 	// result: (MOVWconst [-c])
 	for {
@@ -4748,6 +4770,18 @@ func rewriteValueMIPS_OpMIPSSUB(v *Value) bool {
 		v.AddArg(x)
 		return true
 	}
+	// match: (SUB x (NEG y))
+	// result: (ADD x y)
+	for {
+		x := v_0
+		if v_1.Op != OpMIPSNEG {
+			break
+		}
+		y := v_1.Args[0]
+		v.reset(OpMIPSADD)
+		v.AddArg2(x, y)
+		return true
+	}
 	// match: (SUB x x)
 	// result: (MOVWconst [0])
 	for {

test/codegen/arithmetic.go

@@ -92,6 +92,7 @@ func SubFromConst(a int) int {
 
 func SubFromConstNeg(a int) int {
 	// loong64: "ADDV[U]\t\\$40"
+	// mips: "ADD[U]\t\\$40"
 	// mips64: "ADDV[U]\t\\$40"
 	// ppc64x: `ADD\t[$]40,\sR[0-9]+,\sR`
 	// riscv64: "ADDI\t\\$40",-"NEG"
@@ -101,6 +102,7 @@ func SubFromConstNeg(a int) int {
 
 func SubSubFromConst(a int) int {
 	// loong64: "ADDV[U]\t\\$20"
+	// mips: "ADD[U]\t\\$20"
 	// mips64: "ADDV[U]\t\\$20"
 	// ppc64x: `ADD\t[$]20,\sR[0-9]+,\sR`
 	// riscv64: "ADDI\t\\$20",-"NEG"
@@ -117,6 +119,7 @@ func AddSubFromConst(a int) int {
 
 func NegSubFromConst(a int) int {
 	// loong64: "ADDV[U]\t\\$-20"
+	// mips: "ADD[U]\t\\$-20"
 	// mips64: "ADDV[U]\t\\$-20"
 	// ppc64x: `ADD\t[$]-20,\sR[0-9]+,\sR`
 	// riscv64: "ADDI\t\\$-20"
@@ -126,6 +129,7 @@ func NegSubFromConst(a int) int {
 
 func NegAddFromConstNeg(a int) int {
 	// loong64: "ADDV[U]\t\\$-40","SUBV"
+	// mips: "ADD[U]\t\\$-40","SUB"
 	// mips64: "ADDV[U]\t\\$-40","SUBV"
 	// ppc64x: `SUBC\tR[0-9]+,\s[$]40,\sR`
 	// riscv64: "ADDI\t\\$-40","NEG"
@@ -136,6 +140,7 @@ func NegAddFromConstNeg(a int) int {
 func SubSubNegSimplify(a, b int) int {
 	// amd64:"NEGQ"
 	// loong64:"SUBV"
+	// mips:"SUB"
 	// mips64:"SUBV"
 	// ppc64x:"NEG"
 	// riscv64:"NEG",-"SUB"
@@ -146,6 +151,7 @@ func SubSubNegSimplify(a, b int) int {
 func SubAddSimplify(a, b int) int {
 	// amd64:-"SUBQ",-"ADDQ"
 	// loong64:-"SUBV",-"ADDV"
+	// mips:-"SUB",-"ADD"
 	// mips64:-"SUBV",-"ADDV"
 	// ppc64x:-"SUB",-"ADD"
 	// riscv64:-"SUB",-"ADD"
@@ -155,6 +161,7 @@ func SubAddSimplify(a, b int) int {
 
 func SubAddSimplify2(a, b, c int) (int, int, int, int, int, int) {
 	// amd64:-"ADDQ"
+	// mips:"SUB",-"ADD"
 	// mips64:"SUBV",-"ADDV"
 	// loong64:"SUBV",-"ADDV"
 	r := (a + b) - (a + c)
@@ -165,6 +172,7 @@ func SubAddSimplify2(a, b, c int) (int, int, int, int, int, int) {
 	// amd64:-"ADDQ"
 	r3 := (b + a) - (c + a)
 	// amd64:-"SUBQ"
+	// mips:"ADD",-"SUB"
 	// mips64:"ADDV",-"SUBV"
 	// loong64:"ADDV",-"SUBV"
 	r4 := (a - c) + (c + b)
@@ -176,6 +184,7 @@ func SubAddSimplify2(a, b, c int) (int, int, int, int, int, int) {
 func SubAddNegSimplify(a, b int) int {
 	// amd64:"NEGQ",-"ADDQ",-"SUBQ"
 	// loong64:"SUBV",-"ADDV"
+	// mips:"SUB",-"ADD"
 	// mips64:"SUBV",-"ADDV"
 	// ppc64x:"NEG",-"ADD",-"SUB"
 	// riscv64:"NEG",-"ADD",-"SUB"
@@ -186,6 +195,7 @@ func SubAddNegSimplify(a, b int) int {
 func AddAddSubSimplify(a, b, c int) int {
 	// amd64:-"SUBQ"
 	// loong64:"ADDV",-"SUBV"
+	// mips:"ADD",-"SUB"
 	// mips64:"ADDV",-"SUBV"
 	// ppc64x:-"SUB"
 	// riscv64:"ADD","ADD",-"SUB"