[tree-ssa] DCE broken

[Steven Bosscher <s dot bosscher at student dot tudelft dot nl>]

Hello,

Still playing with the same test snippet, now with tree-ssa current CVS

int main()
{
int bla, foo, bar;
  bla = 1;
  foo = 2*bla;
  bar = 2*bla+1;
  goto waffle;
  return bar;
waffle:
  bla = 1;
  printf("%d\n",bar);
  return bar;
}

bar always has a value (3) at the end of this function, and running the
compiled program should produce the output "3" (doh!). If compiled with
-O1 -ftree-dce, there is no output.

The ".optimized" dump suggests that all expressions are killed. The
".dce" dump does not show that DCE killed them , however compiling
without the -ftree-dce flag produces the correct output. So, DCE is
broken, and the DCE dump is apparently broken too...

It almost looks as if DCE kills all *necessary* code :-)

Greetz
Steven



steven:~/gcc/play # gcc-ssa -fdump-tree-all-ssa -ftree-dce -O1 ssa-test.c
steven:~/gcc/play # cat ssa-test.c.t04.simple
main()
{
  int bla;
  int foo;
  int bar;
  int T.1;
  bla = 1;
  foo = bla * 2;
  T.1 = bla * 2;
  bar = T.1 + 1;
  goto waffle;
  return bar;
  waffle:
  bla = 1;
  printf ((const char *)(char *)"%d\n", bar);
  return bar;
}

steven:~/gcc/play # cat ssa-test.c.t10.dce       
main
{
  int bla;
  int foo;
  int bar;
  int T.1;
  bla = 1;
  foo = bla * 2;
  T.1 = bla * 2;
  bar = T.1 + 1;
  goto waffle;
  return bar;
  waffle:
  bla = 1;
  printf ((const char *)(char *)"%d\n", bar);
  return bar;
}
steven:~/gcc/play # cat ssa-test.c.t11.optimized 
main()
{
  int bla;
  int foo;
  int bar;
  int T.1;
  goto waffle;
  return bar;
  waffle:
  return bar;
}

steven:~/gcc/play #