[tree-ssa] dom1 bug.

[Andrew MacLeod <amacleod at redhat dot com>]

Here's the first bit of fallout from using my operand freelist.

dom1 appears to lose VDEFs from time to time when it rewrites stmts. A
lot of the failures I am seeing are related to dropped VDEFS.

This illustrates the point: Compile with -O2 and look at the dom1
listing

Andrew


/* This is testcase 990130-1.c.  Compile with -O2 */


int count = 0;
int dummy;

static int *
bar(void)
{
  ++count;
  return &dummy;
}

static void
foo(void)
{
  asm("" : "+r"(*bar()));
}

main()
{
  foo();
  if (count != 1)
    abort();
  exit(0);
}

/* The code coming into dom1 looks like:

    <D1072>_5 = &dummy;
  <L0>:;
    retval.6_6 = <D1072>_5;
    T.3_7 = retval.6_6;
    #   VUSE <count_4>;
    #   VUSE <dummy_8>;
    T.4_9 = *T.3_7;
    #   count_10 = VDEF <count_4>;
    #   dummy_11 = VDEF <dummy_8>;
    __asm__("":"=r" *T.3_7:"0" T.4_9);
    #   VUSE <count_10>;
    count.5_12 = count;


Dom1  replaces *T.3_7 with 'dummy':
  <D1072>_5 = &dummy;

<L0>:;
  retval.6_6 = &dummy;
  T.3_7 = &dummy;
  #   VUSE <dummy_8>;
  T.4_9 = dummy;
  #   dummy_11 = VDEF <dummy_8>;
  __asm__("":"=r" dummy:"0" T.4_9);
  #   VUSE <count_10>;
  count.5_12 = count;


It removes the VDEF for count_10 from the ASM, so the VUSE of count_10
now has no definition.

*/