Fix compile time and memory usage issues from previous fix

[Jack Howarth]

Daniel,
    I haven't seen this mentioned yet in the thread here but your
latest changes seem to be causing new regressions in the gcc testsuite...

FAIL: gcc.dg/tree-ssa/loadpre1.c scan-tree-dump-times Eliminated: 1 1
FAIL: gcc.dg/tree-ssa/loadpre14.c scan-tree-dump-times Eliminated: 1 1
FAIL: gcc.dg/tree-ssa/loadpre15.c scan-tree-dump-times Eliminated: 1 1
FAIL: gcc.dg/tree-ssa/pr26421.c scan-tree-dump-times V_MAY_DEF 1

on powerpc-apple-darwin8.5.0. Other targets like  
x86_64-unknown-linux-gnu and ia64-suse-linux-gnu
seem to have these regressions as well.
                Jack