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: 1aad82e62e61e89789932c2070851a023f130dd8
GitHub-Pull-Request: golang/go#59119
Reviewed-on: https://go-review.googlesource.com/c/go/+/477555
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go
index 2f06ac58d6..f381b34ade 100644
--- a/test/codegen/arithmetic.go
+++ b/test/codegen/arithmetic.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"