[MLton-commit] r4370

[Stephen Weeks]

Fixed a bug in the SSA simplifier.  Redundant tests didn't count the
start label of a function as an occurrence, and hence the in-degree of
the start block could be too low.  This caused an incorrect
elimination of an irredundant test, in examples like the following.

fun f () = loop ()
  loop ()
    b: bool = WordR_equal (w1, w2)
    case b of
      true => loop | false => L_1
  L_1 ()
    return

The problem is that loop was marked as having in-degree one instead of
two, and hence the fact that w1=w2 was propagated to loop in the true
branch, which then causes the test to be redundant.


----------------------------------------------------------------------

U   mlton/trunk/mlton/ssa/redundant-tests.fun

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Modified: mlton/trunk/mlton/ssa/redundant-tests.fun
===================================================================
--- mlton/trunk/mlton/ssa/redundant-tests.fun	2006-03-03 18:51:40 UTC (rev 4369)
+++ mlton/trunk/mlton/ssa/redundant-tests.fun	2006-03-03 19:16:18 UTC (rev 4370)
@@ -192,11 +192,12 @@
                                                          facts = ref [],
                                                          inDeg = ref 0}))
              (* Set up inDeg. *)
+             fun inc l = Int.inc (#inDeg (labelInfo l))
+             val () = inc start
              val _ =
                 Vector.foreach
                 (blocks, fn Block.T {transfer, ...} =>
-                 Transfer.foreachLabel
-                 (transfer, Int.inc o #inDeg o labelInfo))
+                 Transfer.foreachLabel (transfer, inc))
              (* Perform analysis, set up facts, and set up ancestor. *)
              fun loop (Tree.T (Block.T {label, statements, transfer, ...},
                                children),