how to dump ssa-pre debug info

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I am trying to dump the debug info of gcc/tree-ssa-pre.c but did not 
succeed. (using gcc 4.4.3)
I tried -ftree-pre with -fdump-tree-all or -fdump-tree-pre[-all] and 
many more and searched for strings that should have been in one of the 
generated files.

It seems that none of the optimizations are dumped:
  some files
  file.c.98.release-ssa
  file.c.129.optimized
  some more files

Creation of a dump file depends on the dump_file variable.
How can I dump the debug info of optimizations?