runtime: replace all uses of CtzXX with TrailingZerosXX

Replace all uses of Ctz64/32/8 with TrailingZeros64/32/8, because they
are the same and maybe duplicated. Also renamed CtzXX functions in 386
assembly code.

Change-Id: I19290204858083750f4be589bb0923393950ae6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/438935
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Keith Randall <khr@golang.org>

9 files changed, 95 insertions, 129 deletions

diff --git a/src/runtime/internal/sys/intrinsics.go b/src/runtime/internal/sys/intrinsics.go
index 5af49011e9..902d893178 100644
--- a/src/runtime/internal/sys/intrinsics.go
+++ b/src/runtime/internal/sys/intrinsics.go
@@ -5,56 +5,75 @@
 //go:build !386
 
 // TODO finish intrinsifying 386, deadcode the assembly, remove build tags, merge w/ intrinsics_common
-// TODO replace all uses of CtzXX with TrailingZerosXX; they are the same.
 
 package sys
 
-// Using techniques from http://supertech.csail.mit.edu/papers/debruijn.pdf
+// Copied from math/bits to avoid dependence.
 
-const deBruijn64ctz = 0x0218a392cd3d5dbf
-
-var deBruijnIdx64ctz = [64]byte{
-	0, 1, 2, 7, 3, 13, 8, 19,
-	4, 25, 14, 28, 9, 34, 20, 40,
-	5, 17, 26, 38, 15, 46, 29, 48,
-	10, 31, 35, 54, 21, 50, 41, 57,
-	63, 6, 12, 18, 24, 27, 33, 39,
-	16, 37, 45, 47, 30, 53, 49, 56,
-	62, 11, 23, 32, 36, 44, 52, 55,
-	61, 22, 43, 51, 60, 42, 59, 58,
+var deBruijn32tab = [32]byte{
+	0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
+	31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9,
 }
 
-const deBruijn32ctz = 0x04653adf
+const deBruijn32 = 0x077CB531
 
-var deBruijnIdx32ctz = [32]byte{
-	0, 1, 2, 6, 3, 11, 7, 16,
-	4, 14, 12, 21, 8, 23, 17, 26,
-	31, 5, 10, 15, 13, 20, 22, 25,
-	30, 9, 19, 24, 29, 18, 28, 27,
+var deBruijn64tab = [64]byte{
+	0, 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,
+	62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,
+	63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,
+	54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,
 }
 
-// Ctz64 counts trailing (low-order) zeroes,
-// and if all are zero, then 64.
-func Ctz64(x uint64) int {
-	x &= -x                       // isolate low-order bit
-	y := x * deBruijn64ctz >> 58  // extract part of deBruijn sequence
-	i := int(deBruijnIdx64ctz[y]) // convert to bit index
-	z := int((x - 1) >> 57 & 64)  // adjustment if zero
-	return i + z
+const deBruijn64 = 0x03f79d71b4ca8b09
+
+const ntz8tab = "" +
+	"\x08\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x06\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x07\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x06\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +
+	"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00"
+
+// TrailingZeros32 returns the number of trailing zero bits in x; the result is 32 for x == 0.
+func TrailingZeros32(x uint32) int {
+	if x == 0 {
+		return 32
+	}
+	// see comment in TrailingZeros64
+	return int(deBruijn32tab[(x&-x)*deBruijn32>>(32-5)])
 }
 
-// Ctz32 counts trailing (low-order) zeroes,
-// and if all are zero, then 32.
-func Ctz32(x uint32) int {
-	x &= -x                       // isolate low-order bit
-	y := x * deBruijn32ctz >> 27  // extract part of deBruijn sequence
-	i := int(deBruijnIdx32ctz[y]) // convert to bit index
-	z := int((x - 1) >> 26 & 32)  // adjustment if zero
-	return i + z
+// TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.
+func TrailingZeros64(x uint64) int {
+	if x == 0 {
+		return 64
+	}
+	// If popcount is fast, replace code below with return popcount(^x & (x - 1)).
+	//
+	// x & -x leaves only the right-most bit set in the word. Let k be the
+	// index of that bit. Since only a single bit is set, the value is two
+	// to the power of k. Multiplying by a power of two is equivalent to
+	// left shifting, in this case by k bits. The de Bruijn (64 bit) constant
+	// is such that all six bit, consecutive substrings are distinct.
+	// Therefore, if we have a left shifted version of this constant we can
+	// find by how many bits it was shifted by looking at which six bit
+	// substring ended up at the top of the word.
+	// (Knuth, volume 4, section 7.3.1)
+	return int(deBruijn64tab[(x&-x)*deBruijn64>>(64-6)])
 }
 
-// Ctz8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
-func Ctz8(x uint8) int {
+// TrailingZeros8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
+func TrailingZeros8(x uint8) int {
 	return int(ntz8tab[x])
 }
 
diff --git a/src/runtime/internal/sys/intrinsics_386.s b/src/runtime/internal/sys/intrinsics_386.s
index 784b246a01..f33ade0a3a 100644
--- a/src/runtime/internal/sys/intrinsics_386.s
+++ b/src/runtime/internal/sys/intrinsics_386.s
@@ -4,7 +4,7 @@
 
 #include "textflag.h"
 
-TEXT runtime∕internal∕sys·Ctz64(SB), NOSPLIT, $0-12
+TEXT runtime∕internal∕sys·TrailingZeros64(SB), NOSPLIT, $0-12
 	// Try low 32 bits.
 	MOVL	x_lo+0(FP), AX
 	BSFL	AX, AX
@@ -26,7 +26,7 @@ none:
 	MOVL	$64, ret+8(FP)
 	RET
 
-TEXT runtime∕internal∕sys·Ctz32(SB), NOSPLIT, $0-8
+TEXT runtime∕internal∕sys·TrailingZeros32(SB), NOSPLIT, $0-8
 	MOVL	x+0(FP), AX
 	BSFL	AX, AX
 	JNZ	2(PC)
@@ -34,7 +34,7 @@ TEXT runtime∕internal∕sys·Ctz32(SB), NOSPLIT, $0-8
 	MOVL	AX, ret+4(FP)
 	RET
 
-TEXT runtime∕internal∕sys·Ctz8(SB), NOSPLIT, $0-8
+TEXT runtime∕internal∕sys·TrailingZeros8(SB), NOSPLIT, $0-8
 	MOVBLZX	x+0(FP), AX
 	BSFL	AX, AX
 	JNZ	2(PC)
diff --git a/src/runtime/internal/sys/intrinsics_common.go b/src/runtime/internal/sys/intrinsics_common.go
index 7d7af20906..709ec23f9d 100644
--- a/src/runtime/internal/sys/intrinsics_common.go
+++ b/src/runtime/internal/sys/intrinsics_common.go
@@ -6,43 +6,23 @@ package sys
 
 // Copied from math/bits to avoid dependence.
 
-var len8tab = [256]uint8{
-	0x00, 0x01, 0x02, 0x02, 0x03, 0x03, 0x03, 0x03, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04,
-	0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,
-	0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06,
-	0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06,
-	0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
-	0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
-	0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
-	0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-	0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08,
-}
-
-var ntz8tab = [256]uint8{
-	0x08, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x06, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x07, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x06, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-	0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
-}
+const len8tab = "" +
+	"\x00\x01\x02\x02\x03\x03\x03\x03\x04\x04\x04\x04\x04\x04\x04\x04" +
+	"\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05" +
+	"\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06" +
+	"\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06" +
+	"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +
+	"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +
+	"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +
+	"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +
+	"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08"
 
 // len64 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
 //
@@ -102,45 +82,12 @@ func OnesCount64(x uint64) int {
 	return int(x) & (1<<7 - 1)
 }
 
-var deBruijn64tab = [64]byte{
-	0, 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,
-	62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,
-	63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,
-	54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,
-}
-
-const deBruijn64 = 0x03f79d71b4ca8b09
-
-// TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.
-func TrailingZeros64(x uint64) int {
-	if x == 0 {
-		return 64
-	}
-	// If popcount is fast, replace code below with return popcount(^x & (x - 1)).
-	//
-	// x & -x leaves only the right-most bit set in the word. Let k be the
-	// index of that bit. Since only a single bit is set, the value is two
-	// to the power of k. Multiplying by a power of two is equivalent to
-	// left shifting, in this case by k bits. The de Bruijn (64 bit) constant
-	// is such that all six bit, consecutive substrings are distinct.
-	// Therefore, if we have a left shifted version of this constant we can
-	// find by how many bits it was shifted by looking at which six bit
-	// substring ended up at the top of the word.
-	// (Knuth, volume 4, section 7.3.1)
-	return int(deBruijn64tab[(x&-x)*deBruijn64>>(64-6)])
-}
-
 // LeadingZeros64 returns the number of leading zero bits in x; the result is 64 for x == 0.
 func LeadingZeros64(x uint64) int { return 64 - Len64(x) }
 
 // LeadingZeros8 returns the number of leading zero bits in x; the result is 8 for x == 0.
 func LeadingZeros8(x uint8) int { return 8 - Len8(x) }
 
-// TrailingZeros8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
-func TrailingZeros8(x uint8) int {
-	return int(ntz8tab[x])
-}
-
 // Len8 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
 func Len8(x uint8) int {
 	return int(len8tab[x])
diff --git a/src/runtime/internal/sys/intrinsics_stubs.go b/src/runtime/internal/sys/intrinsics_stubs.go
index a020652f76..66cfcded40 100644
--- a/src/runtime/internal/sys/intrinsics_stubs.go
+++ b/src/runtime/internal/sys/intrinsics_stubs.go
@@ -6,8 +6,8 @@
 
 package sys
 
-func Ctz64(x uint64) int
-func Ctz32(x uint32) int
-func Ctz8(x uint8) int
+func TrailingZeros64(x uint64) int
+func TrailingZeros32(x uint32) int
+func TrailingZeros8(x uint8) int
 func Bswap64(x uint64) uint64
 func Bswap32(x uint32) uint32
diff --git a/src/runtime/internal/sys/intrinsics_test.go b/src/runtime/internal/sys/intrinsics_test.go
index 0444183e9d..bf75f19848 100644
--- a/src/runtime/internal/sys/intrinsics_test.go
+++ b/src/runtime/internal/sys/intrinsics_test.go
@@ -5,19 +5,19 @@ import (
 	"testing"
 )
 
-func TestCtz64(t *testing.T) {
+func TestTrailingZeros64(t *testing.T) {
 	for i := 0; i <= 64; i++ {
 		x := uint64(5) << uint(i)
-		if got := sys.Ctz64(x); got != i {
-			t.Errorf("Ctz64(%d)=%d, want %d", x, got, i)
+		if got := sys.TrailingZeros64(x); got != i {
+			t.Errorf("TrailingZeros64(%d)=%d, want %d", x, got, i)
 		}
 	}
 }
-func TestCtz32(t *testing.T) {
+func TestTrailingZeros32(t *testing.T) {
 	for i := 0; i <= 32; i++ {
 		x := uint32(5) << uint(i)
-		if got := sys.Ctz32(x); got != i {
-			t.Errorf("Ctz32(%d)=%d, want %d", x, got, i)
+		if got := sys.TrailingZeros32(x); got != i {
+			t.Errorf("TrailingZeros32(%d)=%d, want %d", x, got, i)
 		}
 	}
 }
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index cece04eeca..70a13d0576 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -816,7 +816,7 @@ var zerobase uintptr
 // nextFreeFast returns the next free object if one is quickly available.
 // Otherwise it returns 0.
 func nextFreeFast(s *mspan) gclinkptr {
-	theBit := sys.Ctz64(s.allocCache) // Is there a free object in the allocCache?
+	theBit := sys.TrailingZeros64(s.allocCache) // Is there a free object in the allocCache?
 	if theBit < 64 {
 		result := s.freeindex + uintptr(theBit)
 		if result < s.nelems {
diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go
index 8a4a61c27d..7cc22309f1 100644
--- a/src/runtime/mbitmap.go
+++ b/src/runtime/mbitmap.go
@@ -147,7 +147,7 @@ func (s *mspan) nextFreeIndex() uintptr {
 
 	aCache := s.allocCache
 
-	bitIndex := sys.Ctz64(aCache)
+	bitIndex := sys.TrailingZeros64(aCache)
 	for bitIndex == 64 {
 		// Move index to start of next cached bits.
 		sfreeindex = (sfreeindex + 64) &^ (64 - 1)
@@ -159,7 +159,7 @@ func (s *mspan) nextFreeIndex() uintptr {
 		// Refill s.allocCache with the next 64 alloc bits.
 		s.refillAllocCache(whichByte)
 		aCache = s.allocCache
-		bitIndex = sys.Ctz64(aCache)
+		bitIndex = sys.TrailingZeros64(aCache)
 		// nothing available in cached bits
 		// grab the next 8 bytes and try again.
 	}
@@ -452,9 +452,9 @@ func (h heapBits) next() (heapBits, uintptr) {
 		if h.mask != 0 {
 			var i int
 			if goarch.PtrSize == 8 {
-				i = sys.Ctz64(uint64(h.mask))
+				i = sys.TrailingZeros64(uint64(h.mask))
 			} else {
-				i = sys.Ctz32(uint32(h.mask))
+				i = sys.TrailingZeros32(uint32(h.mask))
 			}
 			h.mask ^= uintptr(1) << (i & (ptrBits - 1))
 			return h, h.addr + uintptr(i)*goarch.PtrSize
@@ -494,9 +494,9 @@ func (h heapBits) nextFast() (heapBits, uintptr) {
 	// BSFQ
 	var i int
 	if goarch.PtrSize == 8 {
-		i = sys.Ctz64(uint64(h.mask))
+		i = sys.TrailingZeros64(uint64(h.mask))
 	} else {
-		i = sys.Ctz32(uint32(h.mask))
+		i = sys.TrailingZeros32(uint32(h.mask))
 	}
 	// BTCQ
 	h.mask ^= uintptr(1) << (i & (ptrBits - 1))
diff --git a/src/runtime/slice.go b/src/runtime/slice.go
index 134d14f1a0..459dc8891e 100644
--- a/src/runtime/slice.go
+++ b/src/runtime/slice.go
@@ -225,9 +225,9 @@ func growslice(oldPtr unsafe.Pointer, newLen, oldCap, num int, et *_type) slice
 		var shift uintptr
 		if goarch.PtrSize == 8 {
 			// Mask shift for better code generation.
-			shift = uintptr(sys.Ctz64(uint64(et.size))) & 63
+			shift = uintptr(sys.TrailingZeros64(uint64(et.size))) & 63
 		} else {
-			shift = uintptr(sys.Ctz32(uint32(et.size))) & 31
+			shift = uintptr(sys.TrailingZeros32(uint32(et.size))) & 31
 		}
 		lenmem = uintptr(oldLen) << shift
 		newlenmem = uintptr(newLen) << shift
diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index 10c45045d9..87d8e519bd 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -617,7 +617,7 @@ func adjustpointers(scanp unsafe.Pointer, bv *bitvector, adjinfo *adjustinfo, f
 		}
 		b := *(addb(bv.bytedata, i/8))
 		for b != 0 {
-			j := uintptr(sys.Ctz8(b))
+			j := uintptr(sys.TrailingZeros8(b))
 			b &= b - 1
 			pp := (*uintptr)(add(scanp, (i+j)*goarch.PtrSize))
 		retry: