Avoid BM2 in the AVX(1) implementation

I could've also generated all options for with/without BMI2/AVX2, but I
simply went for having the fastest option require AVX2+BMI2 and use
AVX(1) as the fallback.

Author: Jille

asm_amd64.s

@@ -6,10 +6,6 @@ func hasAVX() bool {
 	return true
 }
 
-func hasAVX2() bool {
-	return true
-}
-
-func hasBMI2() bool {
+func hasAVX2AndBMI2() bool {
 	return true
 }

detect_avx2_always.go

@@ -6,10 +6,6 @@ func hasAVX() bool {
 	return false
 }
 
-func hasAVX2() bool {
-	return false
-}
-
-func hasBMI2() bool {
+func hasAVX2AndBMI2() bool {
 	return false
 }

detect_avx2_never.go

@@ -4,14 +4,12 @@ package vectorcmp
 
 import "golang.org/x/sys/cpu"
 
+var axv2AndBmi2 = cpu.X86.HasAVX2 && cpu.X86.HasBMI2
+
 func hasAVX() bool {
 	return cpu.X86.HasAVX
 }
 
-func hasAVX2() bool {
-	return cpu.X86.HasAVX2
-}
-
-func hasBMI2() bool {
-	return cpu.X86.HasBMI2
+func hasAVX2AndBMI2() bool {
+	return axv2AndBmi2
 }

detect_avx2_runtime.go

@@ -6,10 +6,6 @@ func hasAVX() bool {
 	return true
 }
 
-func hasAVX2() bool {
+func hasAVX2AndBMI2() bool {
 	return false
 }
-
-func hasBMI2() bool {
-	return true
-}