cmd/compile: generate tbz/tbnz when comparing against zero on arm64

The tbz/tbnz checks the sign bit to determine if the value is >= 0 or < 0.

go1 benchmark results:
name                   old speed      new speed      delta
JSONEncode             94.4MB/s ± 1%  95.7MB/s ± 0%  +1.36%  (p=0.000 n=10+9)
JSONDecode             19.7MB/s ± 1%  19.9MB/s ± 1%  +1.08%  (p=0.000 n=9+10)
Gzip                   45.5MB/s ± 0%  46.0MB/s ± 0%  +1.06%  (p=0.000 n=10+10)
Revcomp                 376MB/s ± 0%   379MB/s ± 0%  +0.69%  (p=0.000 n=10+10)
RegexpMatchHard_1K     12.6MB/s ± 0%  12.7MB/s ± 0%  +0.57%  (p=0.000 n=10+8)
RegexpMatchMedium_32   3.21MB/s ± 0%  3.22MB/s ± 0%  +0.31%  (p=0.000 n=9+10)
RegexpMatchEasy1_1K    1.27GB/s ± 0%  1.27GB/s ± 0%  +0.23%  (p=0.000 n=9+9)
RegexpMatchHard_32     11.4MB/s ± 0%  11.4MB/s ± 1%  +0.19%  (p=0.036 n=10+8)
RegexpMatchEasy0_1K    1.77GB/s ± 0%  1.77GB/s ± 0%  +0.13%  (p=0.000 n=9+10)
RegexpMatchMedium_1K   19.3MB/s ± 0%  19.3MB/s ± 0%  +0.04%  (p=0.008 n=10+8)
RegexpMatchEasy0_32     131MB/s ± 0%   131MB/s ± 0%    ~     (p=0.211 n=10+10)
GobDecode              57.5MB/s ± 1%  57.6MB/s ± 2%    ~     (p=0.469 n=10+10)
GobEncode              58.6MB/s ± 1%  58.5MB/s ± 2%    ~     (p=0.781 n=10+10)
GoParse                9.40MB/s ± 0%  9.39MB/s ± 0%  -0.19%  (p=0.005 n=10+9)
RegexpMatchEasy1_32     133MB/s ± 0%   133MB/s ± 0%  -0.48%  (p=0.000 n=10+10)
Template               20.9MB/s ± 0%  20.6MB/s ± 0%  -1.54%  (p=0.000 n=8+10)

Change-Id: I411efe44db35c3962445618d5a47c12e31b3925b
Reviewed-on: https://go-review.googlesource.com/92715
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Author: mrosier-qdt

src/cmd/compile/internal/gc/asm_test.go

@@ -2711,6 +2711,46 @@ var linuxARM64Tests = []*asmTest{
 		pos: []string{"LSL\t\\$17"},
 		neg: []string{"CMP"},
 	},
+	{
+		fn: `
+		func $(a int32, ptr *int) {
+			if a >= 0 {
+				*ptr = 0
+			}
+		}
+		`,
+		pos: []string{"TBNZ"},
+	},
+	{
+		fn: `
+		func $(a int64, ptr *int) {
+			if a >= 0 {
+				*ptr = 0
+			}
+		}
+		`,
+		pos: []string{"TBNZ"},
+	},
+	{
+		fn: `
+		func $(a int32, ptr *int) {
+			if a < 0 {
+				*ptr = 0
+			}
+		}
+		`,
+		pos: []string{"TBZ"},
+	},
+	{
+		fn: `
+		func $(a int64, ptr *int) {
+			if a < 0 {
+				*ptr = 0
+			}
+		}
+		`,
+		pos: []string{"TBZ"},
+	},
 }
 
 var linuxMIPSTests = []*asmTest{

src/cmd/compile/internal/ssa/gen/ARM64.rules

@@ -534,6 +534,12 @@
 (ZW  (ANDconst [c] x) yes no) && oneBit(int64(uint32(c))) -> (TBZ  {ntz(int64(uint32(c)))} x yes no)
 (NZW (ANDconst [c] x) yes no) && oneBit(int64(uint32(c))) -> (TBNZ {ntz(int64(uint32(c)))} x yes no)
 
+// Test sign-bit for signed comparisons against zero
+(GE (CMPWconst [0] x) yes no) -> (TBZ  {int64(31)} x yes no)
+(GE (CMPconst [0] x) yes no) -> (TBZ  {int64(63)} x yes no)
+(LT (CMPWconst [0] x) yes no) -> (TBNZ  {int64(31)} x yes no)
+(LT (CMPconst [0] x) yes no) -> (TBNZ  {int64(63)} x yes no)
+
 // fold offset into address
 (ADDconst [off1] (MOVDaddr [off2] {sym} ptr)) -> (MOVDaddr [off1+off2] {sym} ptr)