cmd/compile: clean up ctz ops

Now that we have ops that can return 2 results, have BSF return a result
and flags.  We can then get rid of the redundant comparison and use CMOV
instead of CMOVconst ops.

Get rid of a bunch of the ops we don't use.  Ctz{8,16}, plus all the Clzs,
and CMOVNEs.  I don't think we'll ever use them, and they would be easy
to add back if needed.

Change-Id: I8858a1d017903474ea7e4002fc76a6a86e7bd487
Reviewed-on: https://go-review.googlesource.com/27630
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

4 files changed, 0 insertions, 67 deletions

diff --git a/src/runtime/internal/sys/intrinsics.go b/src/runtime/internal/sys/intrinsics.go
index 08a062f85a..db2cbecc0e 100644
--- a/src/runtime/internal/sys/intrinsics.go
+++ b/src/runtime/internal/sys/intrinsics.go
@@ -30,19 +30,6 @@ var deBruijnIdx32 = [32]byte{
 	30, 9, 19, 24, 29, 18, 28, 27,
 }
 
-const deBruijn16 = 0x09af
-
-var deBruijnIdx16 = [16]byte{
-	0, 1, 2, 5, 3, 9, 6, 11,
-	15, 4, 8, 10, 14, 7, 13, 12,
-}
-
-const deBruijn8 = 0x17
-
-var deBruijnIdx8 = [8]byte{
-	0, 1, 2, 4, 7, 3, 6, 5,
-}
-
 // Ctz64 counts trailing (low-order) zeroes,
 // and if all are zero, then 64.
 func Ctz64(x uint64) uint64 {
@@ -63,26 +50,6 @@ func Ctz32(x uint32) uint32 {
 	return y + z
 }
 
-// Ctz16 counts trailing (low-order) zeroes,
-// and if all are zero, then 16.
-func Ctz16(x uint16) uint16 {
-	x &= -x                      // isolate low-order bit
-	y := x * deBruijn16 >> 12    // extract part of deBruijn sequence
-	y = uint16(deBruijnIdx16[y]) // convert to bit index
-	z := (x - 1) >> 11 & 16      // adjustment if zero
-	return y + z
-}
-
-// Ctz8 counts trailing (low-order) zeroes,
-// and if all are zero, then 8.
-func Ctz8(x uint8) uint8 {
-	x &= -x                    // isolate low-order bit
-	y := x * deBruijn8 >> 5    // extract part of deBruijn sequence
-	y = uint8(deBruijnIdx8[y]) // convert to bit index
-	z := (x - 1) >> 4 & 8      // adjustment if zero
-	return y + z
-}
-
 // Bswap64 returns its input with byte order reversed
 // 0x0102030405060708 -> 0x0807060504030201
 func Bswap64(x uint64) uint64 {
diff --git a/src/runtime/internal/sys/intrinsics_386.s b/src/runtime/internal/sys/intrinsics_386.s
index 1f48e26492..bc63e5ebdf 100644
--- a/src/runtime/internal/sys/intrinsics_386.s
+++ b/src/runtime/internal/sys/intrinsics_386.s
@@ -36,22 +36,6 @@ TEXT runtime∕internal∕sys·Ctz32(SB), NOSPLIT, $0-8
 	MOVL	AX, ret+4(FP)
 	RET
 
-TEXT runtime∕internal∕sys·Ctz16(SB), NOSPLIT, $0-6
-	MOVW	x+0(FP), AX
-	BSFW	AX, AX
-	JNZ	2(PC)
-	MOVW	$16, AX
-	MOVW	AX, ret+4(FP)
-	RET
-
-TEXT runtime∕internal∕sys·Ctz8(SB), NOSPLIT, $0-5
-	MOVBLZX	x+0(FP), AX
-	BSFL	AX, AX
-	JNZ	2(PC)
-	MOVB	$8, AX
-	MOVB	AX, ret+4(FP)
-	RET
-
 TEXT runtime∕internal∕sys·Bswap64(SB), NOSPLIT, $0-16
 	MOVL	x_lo+0(FP), AX
 	MOVL	x_hi+4(FP), BX
diff --git a/src/runtime/internal/sys/intrinsics_stubs.go b/src/runtime/internal/sys/intrinsics_stubs.go
index 079844fda4..d351048f86 100644
--- a/src/runtime/internal/sys/intrinsics_stubs.go
+++ b/src/runtime/internal/sys/intrinsics_stubs.go
@@ -8,7 +8,5 @@ package sys
 
 func Ctz64(x uint64) uint64
 func Ctz32(x uint32) uint32
-func Ctz16(x uint16) uint16
-func Ctz8(x uint8) uint8
 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 097631bc1e..1f2c8daa96 100644
--- a/src/runtime/internal/sys/intrinsics_test.go
+++ b/src/runtime/internal/sys/intrinsics_test.go
@@ -21,22 +21,6 @@ func TestCtz32(t *testing.T) {
 		}
 	}
 }
-func TestCtz16(t *testing.T) {
-	for i := uint(0); i <= 16; i++ {
-		x := uint16(5) << i
-		if got := sys.Ctz16(x); got != uint16(i) {
-			t.Errorf("Ctz16(%d)=%d, want %d", x, got, i)
-		}
-	}
-}
-func TestCtz8(t *testing.T) {
-	for i := uint(0); i <= 8; i++ {
-		x := uint8(5) << i
-		if got := sys.Ctz8(x); got != uint8(i) {
-			t.Errorf("Ctz8(%d)=%d, want %d", x, got, i)
-		}
-	}
-}
 
 func TestBswap64(t *testing.T) {
 	x := uint64(0x1122334455667788)