runtime: delete timediv

Now that the compiler handles constant 64-bit divisions
without function calls on 32-bit systems, we no longer need
to maintain and test a bad custom implementation of 64-bit division.

Change-Id: If28807ad4f86507267ae69bc8f0b09ec18e98b66
Reviewed-on: https://go-review.googlesource.com/c/go/+/716463
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

15 files changed, 27 insertions, 132 deletions

diff --git a/src/runtime/defs1_netbsd_386.go b/src/runtime/defs1_netbsd_386.go
index 16c55def92..cb4d6f1cf1 100644
--- a/src/runtime/defs1_netbsd_386.go
+++ b/src/runtime/defs1_netbsd_386.go
@@ -121,7 +121,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	ts.tv_sec = int64(timediv(ns, 1e9, &ts.tv_nsec))
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs1_netbsd_arm.go b/src/runtime/defs1_netbsd_arm.go
index 77a59d4a05..d31fcd471d 100644
--- a/src/runtime/defs1_netbsd_arm.go
+++ b/src/runtime/defs1_netbsd_arm.go
@@ -123,7 +123,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	ts.tv_sec = int64(timediv(ns, 1e9, &ts.tv_nsec))
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs_freebsd_386.go b/src/runtime/defs_freebsd_386.go
index 42a0faf74d..20ac643ad7 100644
--- a/src/runtime/defs_freebsd_386.go
+++ b/src/runtime/defs_freebsd_386.go
@@ -210,7 +210,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
+	ts.tv_sec = int32(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs_freebsd_arm.go b/src/runtime/defs_freebsd_arm.go
index dbb54da51b..cf61fcade5 100644
--- a/src/runtime/defs_freebsd_arm.go
+++ b/src/runtime/defs_freebsd_arm.go
@@ -182,7 +182,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	ts.tv_sec = int64(timediv(ns, 1e9, &ts.tv_nsec))
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs_linux_386.go b/src/runtime/defs_linux_386.go
index c6c7d7d6d8..d1875954f3 100644
--- a/src/runtime/defs_linux_386.go
+++ b/src/runtime/defs_linux_386.go
@@ -146,7 +146,8 @@ type timespec32 struct {
 
 //go:nosplit
 func (ts *timespec32) setNsec(ns int64) {
-	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
+	ts.tv_sec = int32(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timespec struct {
@@ -156,9 +157,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	var newNS int32
-	ts.tv_sec = int64(timediv(ns, 1e9, &newNS))
-	ts.tv_nsec = int64(newNS)
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int64(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs_linux_arm.go b/src/runtime/defs_linux_arm.go
index ff879fad89..94577fc597 100644
--- a/src/runtime/defs_linux_arm.go
+++ b/src/runtime/defs_linux_arm.go
@@ -105,7 +105,8 @@ type timespec32 struct {
 
 //go:nosplit
 func (ts *timespec32) setNsec(ns int64) {
-	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
+	ts.tv_sec = int32(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timespec struct {
@@ -115,9 +116,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	var newNS int32
-	ts.tv_sec = int64(timediv(ns, 1e9, &newNS))
-	ts.tv_nsec = int64(newNS)
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int64(ns % 1e9)
 }
 
 type stackt struct {
diff --git a/src/runtime/defs_linux_mipsx.go b/src/runtime/defs_linux_mipsx.go
index 5b10b910db..5a446e0595 100644
--- a/src/runtime/defs_linux_mipsx.go
+++ b/src/runtime/defs_linux_mipsx.go
@@ -103,7 +103,8 @@ type timespec32 struct {
 
 //go:nosplit
 func (ts *timespec32) setNsec(ns int64) {
-	ts.tv_sec = timediv(ns, 1e9, &ts.tv_nsec)
+	ts.tv_sec = int32(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timespec struct {
@@ -113,9 +114,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	var newNS int32
-	ts.tv_sec = int64(timediv(ns, 1e9, &newNS))
-	ts.tv_nsec = int64(newNS)
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int64(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs_openbsd_386.go b/src/runtime/defs_openbsd_386.go
index 996745f6f8..c77b5e16cb 100644
--- a/src/runtime/defs_openbsd_386.go
+++ b/src/runtime/defs_openbsd_386.go
@@ -147,7 +147,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	ts.tv_sec = int64(timediv(ns, 1e9, &ts.tv_nsec))
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/defs_openbsd_arm.go b/src/runtime/defs_openbsd_arm.go
index cdda6b4ad1..5393ea4eeb 100644
--- a/src/runtime/defs_openbsd_arm.go
+++ b/src/runtime/defs_openbsd_arm.go
@@ -152,7 +152,8 @@ type timespec struct {
 
 //go:nosplit
 func (ts *timespec) setNsec(ns int64) {
-	ts.tv_sec = int64(timediv(ns, 1e9, &ts.tv_nsec))
+	ts.tv_sec = int64(ns / 1e9)
+	ts.tv_nsec = int32(ns % 1e9)
 }
 
 type timeval struct {
diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index 9f2fcacc30..d6fce72bf0 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -1472,8 +1472,6 @@ func Releasem() {
 	releasem(getg().m)
 }
 
-var Timediv = timediv
-
 type PIController struct {
 	piController
 }
diff --git a/src/runtime/os_dragonfly.go b/src/runtime/os_dragonfly.go
index fbbee64fd3..c34af7f072 100644
--- a/src/runtime/os_dragonfly.go
+++ b/src/runtime/os_dragonfly.go
@@ -113,7 +113,7 @@ func futexsleep1(addr *uint32, val uint32, ns int64) {
 		// The timeout is specified in microseconds - ensure that we
 		// do not end up dividing to zero, which would put us to sleep
 		// indefinitely...
-		timeout = timediv(ns, 1000, nil)
+		timeout = int32(ns / 1000)
 		if timeout == 0 {
 			timeout = 1
 		}
diff --git a/src/runtime/os_plan9.go b/src/runtime/os_plan9.go
index 72a8657985..80c101f1a1 100644
--- a/src/runtime/os_plan9.go
+++ b/src/runtime/os_plan9.go
@@ -486,7 +486,7 @@ func semacreate(mp *m) {
 func semasleep(ns int64) int {
 	gp := getg()
 	if ns >= 0 {
-		ms := timediv(ns, 1000000, nil)
+		ms := int32(ns / 1000000)
 		if ms == 0 {
 			ms = 1
 		}
diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
index 7610802e0f..2ae625580d 100644
--- a/src/runtime/os_windows.go
+++ b/src/runtime/os_windows.go
@@ -664,7 +664,7 @@ func semasleep(ns int64) int32 {
 		start := nanotime()
 		elapsed := int64(0)
 		for {
-			ms := int64(timediv(ns-elapsed, 1000000, nil))
+			ms := (ns - elapsed) / 1000000
 			if ms == 0 {
 				ms = 1
 			}
diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go
index 3ec5c44ebd..43e4c14236 100644
--- a/src/runtime/runtime1.go
+++ b/src/runtime/runtime1.go
@@ -212,10 +212,6 @@ func check() {
 		throw("bad unsafe.Sizeof y1")
 	}
 
-	if timediv(12345*1000000000+54321, 1000000000, &e) != 12345 || e != 54321 {
-		throw("bad timediv")
-	}
-
 	var z uint32
 	z = 1
 	if !atomic.Cas(&z, 1, 2) {
@@ -593,35 +589,6 @@ func setTraceback(level string) {
 	atomic.Store(&traceback_cache, t)
 }
 
-// Poor mans 64-bit division.
-// This is a very special function, do not use it if you are not sure what you are doing.
-// int64 division is lowered into _divv() call on 386, which does not fit into nosplit functions.
-// Handles overflow in a time-specific manner.
-// This keeps us within no-split stack limits on 32-bit processors.
-//
-//go:nosplit
-func timediv(v int64, div int32, rem *int32) int32 {
-	res := int32(0)
-	for bit := 30; bit >= 0; bit-- {
-		if v >= int64(div)<<uint(bit) {
-			v = v - (int64(div) << uint(bit))
-			// Before this for loop, res was 0, thus all these
-			// power of 2 increments are now just bitsets.
-			res |= 1 << uint(bit)
-		}
-	}
-	if v >= int64(div) {
-		if rem != nil {
-			*rem = 0
-		}
-		return 0x7fffffff
-	}
-	if rem != nil {
-		*rem = int32(v)
-	}
-	return res
-}
-
 // Helpers for Go. Must be NOSPLIT, must only call NOSPLIT functions, and must not block.
 
 //go:nosplit
diff --git a/src/runtime/runtime_test.go b/src/runtime/runtime_test.go
index 6c628f8903..c1c63e3cea 100644
--- a/src/runtime/runtime_test.go
+++ b/src/runtime/runtime_test.go
@@ -6,7 +6,6 @@ package runtime_test
 
 import (
 	"flag"
-	"fmt"
 	"internal/asan"
 	"internal/cpu"
 	"internal/msan"
@@ -498,81 +497,6 @@ func TestVersion(t *testing.T) {
 	}
 }
 
-func TestTimediv(t *testing.T) {
-	for _, tc := range []struct {
-		num int64
-		div int32
-		ret int32
-		rem int32
-	}{
-		{
-			num: 8,
-			div: 2,
-			ret: 4,
-			rem: 0,
-		},
-		{
-			num: 9,
-			div: 2,
-			ret: 4,
-			rem: 1,
-		},
-		{
-			// Used by runtime.check.
-			num: 12345*1000000000 + 54321,
-			div: 1000000000,
-			ret: 12345,
-			rem: 54321,
-		},
-		{
-			num: 1<<32 - 1,
-			div: 2,
-			ret: 1<<31 - 1, // no overflow.
-			rem: 1,
-		},
-		{
-			num: 1 << 32,
-			div: 2,
-			ret: 1<<31 - 1, // overflow.
-			rem: 0,
-		},
-		{
-			num: 1 << 40,
-			div: 2,
-			ret: 1<<31 - 1, // overflow.
-			rem: 0,
-		},
-		{
-			num: 1<<40 + 1,
-			div: 1 << 10,
-			ret: 1 << 30,
-			rem: 1,
-		},
-	} {
-		name := fmt.Sprintf("%d div %d", tc.num, tc.div)
-		t.Run(name, func(t *testing.T) {
-			// Double check that the inputs make sense using
-			// standard 64-bit division.
-			ret64 := tc.num / int64(tc.div)
-			rem64 := tc.num % int64(tc.div)
-			if ret64 != int64(int32(ret64)) {
-				// Simulate timediv overflow value.
-				ret64 = 1<<31 - 1
-				rem64 = 0
-			}
-			if ret64 != int64(tc.ret) {
-				t.Errorf("%d / %d got ret %d rem %d want ret %d rem %d", tc.num, tc.div, ret64, rem64, tc.ret, tc.rem)
-			}
-
-			var rem int32
-			ret := Timediv(tc.num, tc.div, &rem)
-			if ret != tc.ret || rem != tc.rem {
-				t.Errorf("timediv %d / %d got ret %d rem %d want ret %d rem %d", tc.num, tc.div, ret, rem, tc.ret, tc.rem)
-			}
-		})
-	}
-}
-
 func BenchmarkProcYield(b *testing.B) {
 	benchN := func(n uint32) func(*testing.B) {
 		return func(b *testing.B) {