cmd/compile: intrinsify math/bits.TrailingZeros on riscv64

For riscv64/rva22u64 and above, we can intrinsify math/bits.TrailingZeros
using the CTZ/CTZW machine instructions.

On a StarFive VisionFive 2 with GORISCV64=rva22u64:

                  │   ctz.b.1    │               ctz.b.2               │
                  │    sec/op    │   sec/op     vs base                │
TrailingZeros-4     25.500n ± 0%   8.052n ± 0%  -68.42% (p=0.000 n=10)
TrailingZeros8-4     14.76n ± 0%   10.74n ± 0%  -27.24% (p=0.000 n=10)
TrailingZeros16-4    26.84n ± 0%   10.74n ± 0%  -59.99% (p=0.000 n=10)
TrailingZeros32-4   25.500n ± 0%   8.052n ± 0%  -68.42% (p=0.000 n=10)
TrailingZeros64-4   25.500n ± 0%   8.052n ± 0%  -68.42% (p=0.000 n=10)
geomean              23.09n        9.035n       -60.88%

Change-Id: I71edf2b988acb7a68e797afda4ee66d7a57d587e
Reviewed-on: https://go-review.googlesource.com/c/go/+/652320
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Mark Ryan <markdryan@rivosinc.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>

1 files changed, 16 insertions, 9 deletions

diff --git a/test/codegen/mathbits.go b/test/codegen/mathbits.go
index 1cee39283d..786fad3bd9 100644
--- a/test/codegen/mathbits.go
+++ b/test/codegen/mathbits.go
@@ -356,28 +356,30 @@ func RotateLeftVariable32(n uint32, m int) uint32 {
 // ------------------------ //
 
 func TrailingZeros(n uint) int {
+	// 386:"BSFL"
 	// amd64/v1,amd64/v2:"BSFQ","MOVL\t\\$64","CMOVQEQ"
 	// amd64/v3:"TZCNTQ"
-	// 386:"BSFL"
 	// arm:"CLZ"
 	// arm64:"RBIT","CLZ"
 	// loong64:"CTZV"
-	// s390x:"FLOGR"
 	// ppc64x/power8:"ANDN","POPCNTD"
 	// ppc64x/power9: "CNTTZD"
+	// riscv64/rva22u64,riscv64/rva23u64: "CTZ\t"
+	// s390x:"FLOGR"
 	// wasm:"I64Ctz"
 	return bits.TrailingZeros(n)
 }
 
 func TrailingZeros64(n uint64) int {
+	// 386:"BSFL","JNE"
 	// amd64/v1,amd64/v2:"BSFQ","MOVL\t\\$64","CMOVQEQ"
 	// amd64/v3:"TZCNTQ"
-	// 386:"BSFL","JNE"
 	// arm64:"RBIT","CLZ"
 	// loong64:"CTZV"
-	// s390x:"FLOGR"
 	// ppc64x/power8:"ANDN","POPCNTD"
 	// ppc64x/power9: "CNTTZD"
+	// riscv64/rva22u64,riscv64/rva23u64: "CTZ\t"
+	// s390x:"FLOGR"
 	// wasm:"I64Ctz"
 	return bits.TrailingZeros64(n)
 }
@@ -389,40 +391,43 @@ func TrailingZeros64Subtract(n uint64) int {
 }
 
 func TrailingZeros32(n uint32) int {
+	// 386:"BSFL"
 	// amd64/v1,amd64/v2:"BTSQ\\t\\$32","BSFQ"
 	// amd64/v3:"TZCNTL"
-	// 386:"BSFL"
 	// arm:"CLZ"
 	// arm64:"RBITW","CLZW"
 	// loong64:"CTZW"
-	// s390x:"FLOGR","MOVWZ"
 	// ppc64x/power8:"ANDN","POPCNTW"
 	// ppc64x/power9: "CNTTZW"
+	// riscv64/rva22u64,riscv64/rva23u64: "CTZW"
+	// s390x:"FLOGR","MOVWZ"
 	// wasm:"I64Ctz"
 	return bits.TrailingZeros32(n)
 }
 
 func TrailingZeros16(n uint16) int {
-	// amd64:"BSFL","ORL\\t\\$65536"
 	// 386:"BSFL\t"
+	// amd64:"BSFL","ORL\\t\\$65536"
 	// arm:"ORR\t\\$65536","CLZ",-"MOVHU\tR"
 	// arm64:"ORR\t\\$65536","RBITW","CLZW",-"MOVHU\tR",-"RBIT\t",-"CLZ\t"
 	// loong64:"CTZV"
-	// s390x:"FLOGR","OR\t\\$65536"
 	// ppc64x/power8:"POPCNTW","ADD\t\\$-1"
 	// ppc64x/power9:"CNTTZD","ORIS\\t\\$1"
+	// riscv64/rva22u64,riscv64/rva23u64: "ORI\t\\$65536","CTZW"
+	// s390x:"FLOGR","OR\t\\$65536"
 	// wasm:"I64Ctz"
 	return bits.TrailingZeros16(n)
 }
 
 func TrailingZeros8(n uint8) int {
-	// amd64:"BSFL","ORL\\t\\$256"
 	// 386:"BSFL"
+	// amd64:"BSFL","ORL\\t\\$256"
 	// arm:"ORR\t\\$256","CLZ",-"MOVBU\tR"
 	// arm64:"ORR\t\\$256","RBITW","CLZW",-"MOVBU\tR",-"RBIT\t",-"CLZ\t"
 	// loong64:"CTZV"
 	// ppc64x/power8:"POPCNTB","ADD\t\\$-1"
 	// ppc64x/power9:"CNTTZD","OR\t\\$256"
+	// riscv64/rva22u64,riscv64/rva23u64: "ORI\t\\$256","CTZW"
 	// s390x:"FLOGR","OR\t\\$256"
 	// wasm:"I64Ctz"
 	return bits.TrailingZeros8(n)
@@ -469,6 +474,7 @@ func IterateBits16(n uint16) int {
 		// amd64/v1,amd64/v2:"BSFL",-"BTSL"
 		// amd64/v3:"TZCNTL"
 		// arm64:"RBITW","CLZW",-"ORR"
+		// riscv64/rva22u64,riscv64/rva23u64: "CTZ\t",-"ORR"
 		i += bits.TrailingZeros16(n)
 		n &= n - 1
 	}
@@ -481,6 +487,7 @@ func IterateBits8(n uint8) int {
 		// amd64/v1,amd64/v2:"BSFL",-"BTSL"
 		// amd64/v3:"TZCNTL"
 		// arm64:"RBITW","CLZW",-"ORR"
+		// riscv64/rva22u64,riscv64/rva23u64: "CTZ\t",-"ORR"
 		i += bits.TrailingZeros8(n)
 		n &= n - 1
 	}