fanzha02 d556c251a1 cmd/compile: add more generic rewrite rules to reassociate (op (op y C) x|C)
With this patch, opt pass can expose more obvious constant-folding
opportunites.

Example:
func test(i int) int {return (i+8)-(i+4)}

The previous version:
  MOVD	"".i(FP), R0
  ADD	$8, R0, R1
  ADD	$4, R0, R0
  SUB	R0, R1, R0
  MOVD	R0, "".~r1+8(FP)
  RET	(R30)

The optimized version:
  MOVD	$4, R0
  MOVD	R0, "".~r1+8(FP)
  RET	(R30)

This patch removes some existing reassociation rules, such as "x+(z-C)",
because the current generic rewrite rules will canonicalize "x-const"
to "x+(-const)", making "x+(z-C)" equal to "x+(z+(-C))".

This patch also adds test cases.

Change-Id: I857108ba0b5fcc18a879eeab38e2551bc4277797
Reviewed-on: https://go-review.googlesource.com/c/go/+/237137
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
2020-08-24 14:52:54 +00:00
..
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The test directory contains tests of the Go tool chain and runtime. It includes black box tests, regression tests, and error output tests. They are run as part of all.bash.

To run just these tests, execute:

../bin/go run run.go

Standard library tests should be written as regular Go tests in the appropriate package.

The tool chain and runtime also have regular Go tests in their packages. The main reasons to add a new test to this directory are:

  • it is most naturally expressed using the test runner; or
  • it is also applicable to gccgo and other Go tool chains.