internal/runtime/maps: return after fatal to help register allocator

Seems simple, but putting the return after fatal ensures that at the
point of the small group loop, no call has happened so the key is
still in a register. This ensures that we don't have to restore the
key from the stack before the comparison on each iteration. That gets
rid of a load from the inner loop.

name                                       old time/op  new time/op  delta
MapAccessHit/Key=int64/Elem=int64/len=6-8  4.01ns ± 6%  3.85ns ± 3%  -3.92%  (p=0.001 n=10+10)

Change-Id: Ia23ac48e6c5522be88f7d9be0ff3489b2dfc52fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/624255
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>

diff --git a/src/internal/runtime/maps/map.go b/src/internal/runtime/maps/map.go
index 46439602470d528dfcbaf52170f670e2fd2c956d..9ebc72a524feb23c877e0334a04fa97559662b32 100644 (file)
--- a/src/internal/runtime/maps/map.go
+++ b/src/internal/runtime/maps/map.go
@@ -560,6 +560,7 @@ func (m *Map) putSlotSmall(typ *abi.SwissMapType, hash uintptr, key unsafe.Point
        match = g.ctrls().matchEmptyOrDeleted()
        if match == 0 {
                fatal("small map with no empty slot (concurrent map writes?)")
+               return nil
        }
 
        i := match.first()

diff --git a/src/internal/runtime/maps/runtime_fast32_swiss.go b/src/internal/runtime/maps/runtime_fast32_swiss.go
index 84c85772f490c20bf6238c767482886ede886e6c..95c2a5ec1f346a4e298eec5e52073276044d6734 100644 (file)
--- a/src/internal/runtime/maps/runtime_fast32_swiss.go
+++ b/src/internal/runtime/maps/runtime_fast32_swiss.go
@@ -27,6 +27,7 @@ func runtime_mapaccess1_fast32(typ *abi.SwissMapType, m *Map, key uint32) unsafe
 
        if m.writing != 0 {
                fatal("concurrent map read and map write")
+               return nil
        }
 
        if m.dirLen == 0 {
@@ -91,6 +92,7 @@ func runtime_mapaccess2_fast32(typ *abi.SwissMapType, m *Map, key uint32) (unsaf
 
        if m.writing != 0 {
                fatal("concurrent map read and map write")
+               return nil, false
        }
 
        if m.dirLen == 0 {

diff --git a/src/internal/runtime/maps/runtime_fast64_swiss.go b/src/internal/runtime/maps/runtime_fast64_swiss.go
index 7c9ce87cdce5a68ee5f7183a32af6505f702a149..d00e4b625846cd59ec559dc5003edb5a42085279 100644 (file)
--- a/src/internal/runtime/maps/runtime_fast64_swiss.go
+++ b/src/internal/runtime/maps/runtime_fast64_swiss.go
@@ -27,6 +27,7 @@ func runtime_mapaccess1_fast64(typ *abi.SwissMapType, m *Map, key uint64) unsafe
 
        if m.writing != 0 {
                fatal("concurrent map read and map write")
+               return nil
        }
 
        if m.dirLen == 0 {
@@ -91,6 +92,7 @@ func runtime_mapaccess2_fast64(typ *abi.SwissMapType, m *Map, key uint64) (unsaf
 
        if m.writing != 0 {
                fatal("concurrent map read and map write")
+               return nil, false
        }
 
        if m.dirLen == 0 {

diff --git a/src/internal/runtime/maps/runtime_faststr_swiss.go b/src/internal/runtime/maps/runtime_faststr_swiss.go
index ab0213ba3350e0c99eacf176383f3e87820d83b4..08172334e73196ed073e2693811e9412de79d35c 100644 (file)
--- a/src/internal/runtime/maps/runtime_faststr_swiss.go
+++ b/src/internal/runtime/maps/runtime_faststr_swiss.go
@@ -55,6 +55,7 @@ func runtime_mapaccess1_faststr(typ *abi.SwissMapType, m *Map, key string) unsaf
 
        if m.writing != 0 {
                fatal("concurrent map read and map write")
+               return nil
        }
 
        hash := typ.Hasher(abi.NoEscape(unsafe.Pointer(&key)), m.seed)
@@ -112,6 +113,7 @@ func runtime_mapaccess2_faststr(typ *abi.SwissMapType, m *Map, key string) (unsa
 
        if m.writing != 0 {
                fatal("concurrent map read and map write")
+               return nil, false
        }
 
        hash := typ.Hasher(abi.NoEscape(unsafe.Pointer(&key)), m.seed)

diff --git a/src/internal/runtime/maps/table.go b/src/internal/runtime/maps/table.go
index 494ede79111d654bae7b27db4c7e966cce21d092..7b3895c0a173951981d2b59080bdd98d524bc370 100644 (file)
--- a/src/internal/runtime/maps/table.go
+++ b/src/internal/runtime/maps/table.go
@@ -608,6 +608,7 @@ func (it *Iter) Next() {
 
        if it.m.writing != 0 {
                fatal("concurrent map iteration and map write")
+               return
        }
 
        if it.dirIdx < 0 {