memory explosion during gcse

[Franz Sirl]

Hi,

with the current mainline and --enable-checking on Linux/PPC gcc uses
excessive memory during gcse (actually in pre_lcm) while compiling
insn-extract.c. After adding another swapfile I saw that the memory usage topped
out at 395MB!

As I would certainly like to continue bootstrapping with --enable-checking on
"normal" machines (lets say ~200-250MB of virtual memory), it would be nice if
someone could look into improvements here. Maybe something else in the compiler
is broken, as 6991 basic blocks seem to be quite a lot.

Attached the preprocessed insn-extract.i.

Franz.