[MLton-commit] r6981

[Wesley Terpstra]

Correct the definition of CFunction.size from r6978 by referring to 
atoms/c-function.fun:136. The previous patch tried to ensure that the GC
invariants were setup before calling GC_size (which runs the collector).
Otherwise, the marking trace of the heap could fail (specifically by tracing
the stack of the current thrad).

Unfortunately, that patch mistakenly set maySwitchThreads=true rather than
mayGC=true. Furthermore, according to c-function.fun, mayGC must also imply
modifiesFrontier and writesStackTop, even though in this case they will never
be modified.


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U   mlton/trunk/mlton/backend/ssa-to-rssa.fun

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Modified: mlton/trunk/mlton/backend/ssa-to-rssa.fun
===================================================================
--- mlton/trunk/mlton/backend/ssa-to-rssa.fun	2008-11-06 19:23:13 UTC (rev 6980)
+++ mlton/trunk/mlton/backend/ssa-to-rssa.fun	2008-11-10 12:20:42 UTC (rev 6981)
@@ -249,19 +249,19 @@
             bytesNeeded = NONE,
             convention = Cdecl,
             ensuresBytesFree = false,
-            mayGC = false,
-            maySwitchThreads = true, (* Ensure the stack has a return address
-                                      * this guards against the GC possibly
-                                      * tracing the current thread's stack.
-                                      *)
-            modifiesFrontier = false,
+            mayGC = true, (* MLton.size works by running the garbage
+                           * collector to trace the heap. Make sure all
+                           * invariants needed to do this safely are true.
+                           *)
+            maySwitchThreads = false,
+            modifiesFrontier = true,
             prototype = (Vector.new2 (CType.gcState, CType.cpointer),
                          SOME (CType.csize ())),
             readsStackTop = true,
             return = Type.csize (),
             symbolScope = Private,
             target = Direct "GC_size",
-            writesStackTop = false}
+            writesStackTop = true}
    end
 
 structure Name =