Usually optimization rules have corresponding priorities, some need to
be run first, some run next, and some run last, which produces the best
code. But currently our optimization rules have no priority, this CL
adds a late lower pass that runs those rules that need to be run at last,
such as split unreasonable constant folding. This pass can be seen as
the second round of the lower pass.

For example:
func foo(a, b uint64) uint64 {
        d := a+0x1234568
        d1 := b+0x1234568
        return d&d1
}
The code generated by the master branch:
	0x0004 00004        ADD     $19088744, R0, R2 // movz+movk+add
	0x0010 00016        ADD     $19088744, R1, R1 // movz+movk+add
	0x001c 00028        AND     R1, R2, R0

This is because the current constant folding optimization rules do not
take into account the range of constants, causing the constant to be
loaded repeatedly. This CL splits these unreasonable constants folding
in the late lower pass. With this CL the generated code:
	0x0004 00004        MOVD    $19088744, R2 // movz+movk
	0x000c 00012        ADD     R0, R2, R3
	0x0010 00016        ADD     R1, R2, R1
	0x0014 00020        AND     R1, R3, R0

This CL also adds constant folding optimization for ADDS instruction.

In addition, in order not to introduce the codegen regression, an
optimization rule is added to change the addition of a negative number
into a subtraction of a positive number.

go1 benchmarks:
name                     old time/op    new time/op    delta
BinaryTree17-8              1.22s ± 1%     1.24s ± 0%  +1.56%  (p=0.008 n=5+5)
Fannkuch11-8                1.54s ± 0%     1.53s ± 0%  -0.69%  (p=0.016 n=4+5)
FmtFprintfEmpty-8          14.1ns ± 0%    14.1ns ± 0%    ~     (p=0.079 n=4+5)
FmtFprintfString-8         26.0ns ± 0%    26.1ns ± 0%  +0.23%  (p=0.008 n=5+5)
FmtFprintfInt-8            32.3ns ± 0%    32.9ns ± 1%  +1.72%  (p=0.008 n=5+5)
FmtFprintfIntInt-8         54.5ns ± 0%    55.5ns ± 0%  +1.83%  (p=0.008 n=5+5)
FmtFprintfPrefixedInt-8    61.5ns ± 0%    62.0ns ± 0%  +0.93%  (p=0.008 n=5+5)
FmtFprintfFloat-8          72.0ns ± 0%    73.6ns ± 0%  +2.24%  (p=0.008 n=5+5)
FmtManyArgs-8               221ns ± 0%     224ns ± 0%  +1.22%  (p=0.008 n=5+5)
GobDecode-8                1.91ms ± 0%    1.93ms ± 0%  +0.98%  (p=0.008 n=5+5)
GobEncode-8                1.40ms ± 1%    1.39ms ± 0%  -0.79%  (p=0.032 n=5+5)
Gzip-8                      115ms ± 0%     117ms ± 1%  +1.17%  (p=0.008 n=5+5)
Gunzip-8                   19.4ms ± 1%    19.3ms ± 0%  -0.71%  (p=0.016 n=5+4)
HTTPClientServer-8         27.0µs ± 0%    27.3µs ± 0%  +0.80%  (p=0.008 n=5+5)
JSONEncode-8               3.36ms ± 1%    3.33ms ± 0%    ~     (p=0.056 n=5+5)
JSONDecode-8               17.5ms ± 2%    17.8ms ± 0%  +1.71%  (p=0.016 n=5+4)
Mandelbrot200-8            2.29ms ± 0%    2.29ms ± 0%    ~     (p=0.151 n=5+5)
GoParse-8                  1.35ms ± 1%    1.36ms ± 1%    ~     (p=0.056 n=5+5)
RegexpMatchEasy0_32-8      24.5ns ± 0%    24.5ns ± 0%    ~     (p=0.444 n=4+5)
RegexpMatchEasy0_1K-8       131ns ±11%     118ns ± 6%    ~     (p=0.056 n=5+5)
RegexpMatchEasy1_32-8      22.9ns ± 0%    22.9ns ± 0%    ~     (p=0.905 n=4+5)
RegexpMatchEasy1_1K-8       126ns ± 0%     127ns ± 0%    ~     (p=0.063 n=4+5)
RegexpMatchMedium_32-8      486ns ± 5%     483ns ± 0%    ~     (p=0.381 n=5+4)
RegexpMatchMedium_1K-8     15.4µs ± 1%    15.5µs ± 0%    ~     (p=0.151 n=5+5)
RegexpMatchHard_32-8        687ns ± 0%     686ns ± 0%    ~     (p=0.103 n=5+5)
RegexpMatchHard_1K-8       20.7µs ± 0%    20.7µs ± 1%    ~     (p=0.151 n=5+5)
Revcomp-8                   175ms ± 2%     176ms ± 3%    ~     (p=1.000 n=5+5)
Template-8                 20.4ms ± 6%    20.1ms ± 2%    ~     (p=0.151 n=5+5)
TimeParse-8                 112ns ± 0%     113ns ± 0%  +0.97%  (p=0.016 n=5+4)
TimeFormat-8                156ns ± 0%     145ns ± 0%  -7.14%  (p=0.029 n=4+4)

Change-Id: I3ced26e89041f873ac989586514ccc5ee09f13da
Reviewed-on: https://go-review.googlesource.com/c/go/+/425134


Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Eric Fang <eric.fang@arm.com>