runtime: move map ismapkey check to the compiler

Remove the runtime ismapkey check from makemap and
add a check that the map key type supports comparison
to the hmap construction in the compiler.

Move the ismapkey check for the reflect code path
into reflect_makemap.

Change-Id: I718f79b0670c05b63ef31721e72408f59ec4ae86
Reviewed-on: https://go-review.googlesource.com/61035
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -171,6 +171,9 @@ func bmap(t *types.Type) *types.Type {
 	dowidth(bucket)
 
 	// Check invariants that map code depends on.
+	if !IsComparable(t.Key()) {
+		Fatalf("unsupported map key type for %v", t)
+	}
 	if BUCKETSIZE < 8 {
 		Fatalf("bucket size too small for proper alignment")
 	}

src/runtime/hashmap.go

@@ -296,10 +296,6 @@ func makemap(t *maptype, hint int, h *hmap) *hmap {
 		hint = 0
 	}
 
-	if !ismapkey(t.key) {
-		throw("runtime.makemap: unsupported map key type")
-	}
-
 	if evacuatedX+1 != evacuatedY {
 		// evacuate relies on this relationship
 		throw("bad evacuatedN")
@@ -1157,6 +1153,9 @@ func reflect_makemap(t *maptype, cap int) *hmap {
 		println("runtime: sizeof(hmap) =", sz, ", t.hmap.size =", t.hmap.size)
 		throw("bad hmap size")
 	}
+	if !ismapkey(t.key) {
+		throw("runtime.reflect_makemap: unsupported map key type")
+	}
 	if t.key.size > maxKeySize && (!t.indirectkey || t.keysize != uint8(sys.PtrSize)) ||
 		t.key.size <= maxKeySize && (t.indirectkey || t.keysize != uint8(t.key.size)) {
 		throw("key size wrong")