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 {
