simplemerge: don't calculate conflict labels when resolving automatically

Differential Revision: https://phab.mercurial-scm.org/D11903

mercurial/simplemerge.py

@@ -503,13 +503,6 b' def simplemerge(ui, localctx, basectx, o'
         # repository usually sees) might be more useful.
         return _verifytext(ctx.decodeddata(), ctx.path(), ui, opts)
 
-    mode = opts.get('mode', b'merge')
-    name_a, name_b, name_base = None, None, None
-    if mode != b'union':
-        name_a, name_b, name_base = _picklabels(
-            [localctx.path(), otherctx.path(), None], opts.get('label', [])
-        )
-
     try:
         localtext = readctx(localctx)
         basetext = readctx(basectx)
@@ -519,13 +512,18 b' def simplemerge(ui, localctx, basectx, o'
 
     m3 = Merge3Text(basetext, localtext, othertext)
     conflicts = False
+    mode = opts.get('mode', b'merge')
     if mode == b'union':
         lines = _resolve(m3, (1, 2))
     elif mode == b'local':
         lines = _resolve(m3, (1,))
     elif mode == b'other':
         lines = _resolve(m3, (2,))
-    elif mode == b'mergediff':
+    else:
+        name_a, name_b, name_base = _picklabels(
+            [localctx.path(), otherctx.path(), None], opts.get('label', [])
+        )
+        if mode == b'mergediff':
         lines, conflicts = _mergediff(m3, name_a, name_b, name_base)
     else:
         extrakwargs = {