runtime: on map update, don't overwrite key if we don't need to.
Keep track of which types of keys need an update and which don't.
Strings need an update because the new key might pin a smaller backing store.
Floats need an update because it might be +0/-0.
Interfaces need an update because they may contain strings or floats.
Fixes #11088
Change-Id: I9ade53c1dfb3c1a2870d68d07201bc8128e9f217
Reviewed-on: https://go-review.googlesource.com/10843
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/cmd/compile/internal/gc/reflect.go b/src/cmd/compile/internal/gc/reflect.go
index f579ef8..3e69056 100644
--- a/src/cmd/compile/internal/gc/reflect.go
+++ b/src/cmd/compile/internal/gc/reflect.go
@@ -943,10 +943,8 @@
return s
}
-/*
- * Returns 1 if t has a reflexive equality operator.
- * That is, if x==x for all x of type t.
- */
+// isreflexive reports whether t has a reflexive equality operator.
+// That is, if x==x for all x of type t.
func isreflexive(t *Type) bool {
switch t.Etype {
case TBOOL,
@@ -987,7 +985,6 @@
return false
}
}
-
return true
default:
@@ -996,6 +993,56 @@
}
}
+// needkeyupdate reports whether map updates with t as a key
+// need the key to be updated.
+func needkeyupdate(t *Type) bool {
+ switch t.Etype {
+ case TBOOL,
+ TINT,
+ TUINT,
+ TINT8,
+ TUINT8,
+ TINT16,
+ TUINT16,
+ TINT32,
+ TUINT32,
+ TINT64,
+ TUINT64,
+ TUINTPTR,
+ TPTR32,
+ TPTR64,
+ TUNSAFEPTR,
+ TCHAN:
+ return false
+
+ case TFLOAT32, // floats can be +0/-0
+ TFLOAT64,
+ TCOMPLEX64,
+ TCOMPLEX128,
+ TINTER,
+ TSTRING: // strings might have smaller backing stores
+ return true
+
+ case TARRAY:
+ if Isslice(t) {
+ Fatalf("slice can't be a map key: %v", t)
+ }
+ return needkeyupdate(t.Type)
+
+ case TSTRUCT:
+ for t1 := t.Type; t1 != nil; t1 = t1.Down {
+ if needkeyupdate(t1.Type) {
+ return true
+ }
+ }
+ return false
+
+ default:
+ Fatalf("bad type for map key: %v", t)
+ return true
+ }
+}
+
func dtypesym(t *Type) *Sym {
// Replace byte, rune aliases with real type.
// They've been separate internally to make error messages
@@ -1176,6 +1223,7 @@
ot = duint16(s, ot, uint16(mapbucket(t).Width))
ot = duint8(s, ot, uint8(obj.Bool2int(isreflexive(t.Down))))
+ ot = duint8(s, ot, uint8(obj.Bool2int(needkeyupdate(t.Down))))
case TPTR32, TPTR64:
if t.Type.Etype == TANY {
diff --git a/src/reflect/type.go b/src/reflect/type.go
index 95eaf2c..e98c960 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -347,6 +347,7 @@
indirectvalue uint8 // store ptr to value instead of value itself
bucketsize uint16 // size of bucket
reflexivekey bool // true if k==k for all keys
+ needkeyupdate bool // true if we need to update key on an overwrite
}
// ptrType represents a pointer type.
@@ -1525,6 +1526,7 @@
}
mt.bucketsize = uint16(mt.bucket.size)
mt.reflexivekey = isReflexive(ktyp)
+ mt.needkeyupdate = needKeyUpdate(ktyp)
mt.uncommonType = nil
mt.ptrToThis = nil
@@ -1669,6 +1671,33 @@
}
}
+// needKeyUpdate reports whether map overwrites require the key to be copied.
+func needKeyUpdate(t *rtype) bool {
+ switch t.Kind() {
+ case Bool, Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr, Chan, Ptr, UnsafePointer:
+ return false
+ case Float32, Float64, Complex64, Complex128, Interface, String:
+ // Float keys can be updated from +0 to -0.
+ // String keys can be updated to use a smaller backing store.
+ // Interfaces might have floats of strings in them.
+ return true
+ case Array:
+ tt := (*arrayType)(unsafe.Pointer(t))
+ return needKeyUpdate(tt.elem)
+ case Struct:
+ tt := (*structType)(unsafe.Pointer(t))
+ for _, f := range tt.fields {
+ if needKeyUpdate(f.typ) {
+ return true
+ }
+ }
+ return false
+ default:
+ // Func, Map, Slice, Invalid
+ panic("needKeyUpdate called on non-key type " + t.String())
+ }
+}
+
// Make sure these routines stay in sync with ../../runtime/hashmap.go!
// These types exist only for GC, so we only fill out GC relevant info.
// Currently, that's just size and the GC program. We also fill in string
diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go
index 9eca9cf..2db73bc 100644
--- a/src/runtime/hashmap.go
+++ b/src/runtime/hashmap.go
@@ -460,7 +460,9 @@
continue
}
// already have a mapping for key. Update it.
- typedmemmove(t.key, k2, key)
+ if t.needkeyupdate {
+ typedmemmove(t.key, k2, key)
+ }
v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
v2 := v
if t.indirectvalue {
diff --git a/src/runtime/type.go b/src/runtime/type.go
index 1321af8..033f12f 100644
--- a/src/runtime/type.go
+++ b/src/runtime/type.go
@@ -67,6 +67,7 @@
indirectvalue bool // store ptr to value instead of value itself
bucketsize uint16 // size of bucket
reflexivekey bool // true if k==k for all keys
+ needkeyupdate bool // true if we need to update key on an overwrite
}
type chantype struct {
