cmd/compile: add rewrite rules for arithmetic operations

Add the following common local transformations

(t + x) - (t + y) == x - y
(t + x) - (y + t) == x - y
(x + t) - (y + t) == x - y
(x + t) - (t + y) == x - y
(x - t) + (t + y) == x + y
(x - t) + (y + t) == x + y

The compiler itself matches such patterns many times. This also aligns with other popular compilers.

Fixes #59111

Change-Id: Ibdfdb414782f8fcaa20b84ac5d43d0d9ae2c7b60
GitHub-Last-Rev: 1aad82e
GitHub-Pull-Request: #59119
Reviewed-on: https://go-review.googlesource.com/c/go/+/477555
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Keith Randall <[email protected]>

Author: y1yang0

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

@@ -573,6 +573,16 @@
 (Sub(64|32|16|8) (Com(64|32|16|8) x) (Neg(64|32|16|8) x)) => (Const(64|32|16|8) [-1])
 (Add(64|32|16|8) (Com(64|32|16|8) x)                  x)  => (Const(64|32|16|8) [-1])
 
+// Simplification when involving common integer
+// (t + x) - (t + y) == x - y
+// (t + x) - (y + t) == x - y
+// (x + t) - (y + t) == x - y
+// (x + t) - (t + y) == x - y
+// (x - t) + (t + y) == x + y
+// (x - t) + (y + t) == x + y
+(Sub(64|32|16|8) (Add(64|32|16|8) t x) (Add(64|32|16|8) t y)) => (Sub(64|32|16|8) x y)
+(Add(64|32|16|8) (Sub(64|32|16|8) x t) (Add(64|32|16|8) t y)) => (Add(64|32|16|8) x y)
+
 // ^(x-1) == ^x+1 == -x
 (Add(64|32|16|8) (Const(64|32|16|8) [1]) (Com(64|32|16|8) x)) => (Neg(64|32|16|8) x)
 (Com(64|32|16|8) (Add(64|32|16|8) (Const(64|32|16|8) [-1]) x)) => (Neg(64|32|16|8) x)

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

@@ -92,6 +92,22 @@ func SubAddSimplify(a, b int) int {
 	return r
 }
 
+func SubAddSimplify2(a, b, c int) (int, int, int, int, int, int) {
+	// amd64:-"ADDQ"
+	r := (a + b) - (a + c)
+	// amd64:-"ADDQ"
+	r1 := (a + b) - (c + a)
+	// amd64:-"ADDQ"
+	r2 := (b + a) - (a + c)
+	// amd64:-"ADDQ"
+	r3 := (b + a) - (c + a)
+	// amd64:-"SUBQ"
+	r4 := (a - c) + (c + b)
+	// amd64:-"SUBQ"
+	r5 := (a - c) + (b + c)
+	return r, r1, r2, r3, r4, r5
+}
+
 func SubAddNegSimplify(a, b int) int {
 	// amd64:"NEGQ",-"ADDQ",-"SUBQ"
 	// ppc64x:"NEG",-"ADD",-"SUB"