cmd/compile: eliminate unnecessary sign/zero extension for riscv64
Add additional rules to eliminate unnecessary sign/zero extension for riscv64.
Also where possible, replace an extension following a load with a different typed
load. This removes almost another 8,000 instructions from the go binary.
Of particular note, change Eq16/Eq8/Neq16/Neq8 to zero extend each value before
subtraction, rather than zero extending after subtraction. While this appears to
double the number of zero extensions, it often lets us completely eliminate them
as the load can already be performed in a properly typed manner.
As an example, prior to this change runtime.memequal16 was:
0000000000013028 <runtime.memequal16>:
13028:
00813183 ld gp,8(sp)
1302c:
00019183 lh gp,0(gp)
13030:
01013283 ld t0,16(sp)
13034:
00029283 lh t0,0(t0)
13038:
405181b3 sub gp,gp,t0
1303c:
03019193 slli gp,gp,0x30
13040:
0301d193 srli gp,gp,0x30
13044:
0011b193 seqz gp,gp
13048:
00310c23 sb gp,24(sp)
1304c:
00008067 ret
Whereas it now becomes:
0000000000012fa8 <runtime.memequal16>:
12fa8:
00813183 ld gp,8(sp)
12fac:
0001d183 lhu gp,0(gp)
12fb0:
01013283 ld t0,16(sp)
12fb4:
0002d283 lhu t0,0(t0)
12fb8:
405181b3 sub gp,gp,t0
12fbc:
0011b193 seqz gp,gp
12fc0:
00310c23 sb gp,24(sp)
12fc4:
00008067 ret
Change-Id: I16321feb18381241cab121c0097a126104c56c2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/264659
Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>