cmd/compile: incorrect use of CMN on arm64 #50854
Description
% go version
go version devel go1.18-78d3202a14 Sun Jan 16 12:20:41 2022 -0500 darwin/arm64
% cat x.go
package main
//go:noinline
func f(p int64, x, y int64, b bool) bool { return -x <= p && b }
func main() { println(f(1, -1<<63, 1<<63-1, true)) }
% go run x.go
true
% go tool compile -S x.go
"".f STEXT size=32 args=0x20 locals=0x0 funcid=0x0 align=0x0 leaf
0x0000 00000 (x.go:4) TEXT "".f(SB), LEAF|NOFRAME|ABIInternal, $0-32
0x0000 00000 (x.go:4) FUNCDATA ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (x.go:4) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (x.go:4) FUNCDATA $5, "".f.arginfo1(SB)
0x0000 00000 (x.go:4) FUNCDATA $6, "".f.argliveinfo(SB)
0x0000 00000 (x.go:4) PCDATA $3, $1
0x0000 00000 (x.go:4) NEG R1, R1
0x0004 00004 (x.go:4) CMP R1, R0
0x0008 00008 (x.go:4) CSET GE, R1
0x000c 00012 (x.go:4) AND R3, R1, R0
0x0010 00016 (x.go:4) RET (R30)
0x0000 e1 03 01 cb 1f 00 01 eb e1 b7 9f 9a 20 00 03 8a ............ ...
0x0010 c0 03 5f d6 00 00 00 00 00 00 00 00 00 00 00 00 .._.............
So far so good. Note that -x <= p is implemented as NEG, CMP.
Now let's change the body of f: s/b/p <= y/.
% cat x.go
package main
//go:noinline
func f(p int64, x, y int64, b bool) bool { return -x <= p && p <= y }
func main() { println(f(1, -1<<63, 1<<63-1, true)) }
% go run x.go
false
% go tool compile -S x.go
"".f STEXT size=32 args=0x20 locals=0x0 funcid=0x0 align=0x0 leaf
0x0000 00000 (x.go:4) TEXT "".f(SB), LEAF|NOFRAME|ABIInternal, $0-32
0x0000 00000 (x.go:4) FUNCDATA ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (x.go:4) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (x.go:4) FUNCDATA $5, "".f.arginfo1(SB)
0x0000 00000 (x.go:4) FUNCDATA $6, "".f.argliveinfo(SB)
0x0000 00000 (x.go:4) PCDATA $3, $1
0x0000 00000 (x.go:4) CMN R1, R0
0x0004 00004 (x.go:4) BLT 20
0x0008 00008 (x.go:4) CMP R0, R2
0x000c 00012 (x.go:4) CSET GE, R1
0x0010 00016 (x.go:4) JMP 24
0x0014 00020 (x.go:4) MOVD ZR, R1
0x0018 00024 (x.go:4) MOVD R1, R0
0x001c 00028 (x.go:4) RET (R30)
0x0000 1f 00 01 ab 8b 00 00 54 5f 00 00 eb e1 b7 9f 9a .......T_.......
0x0010 02 00 00 14 01 00 80 d2 e0 03 01 aa c0 03 5f d6 .............._.
Note that the NEG, CMP has changed to CMN. The CMN is wrong in the case where the comparison argument is -1<<63, since its negation is itself.
This optimization should not be applied when compiling -x <= p.