[Bug rtl-optimization/31848] New: [4.3 regression] Invalid loop optimization causes bootstrap failure in genautomata

[rearnsha at gcc dot gnu dot org]

Compiling genautomata with -O2 on ARM results in a program that segfaults when
run.  The problem is in  output_min_issue_delay_table.  What appears to be
happening is that the RTL loop optimizer is identifying a loop invariant and
hoisting it.  However, the particular instance of the invariant that is being
hoisted has a REG_EQUAL (const_int 0) note attached, so when the invariant gets
spilled, the value of 0 is substituted instead of the address of the array. 
Essentially, the loop seems to consist of 

x = malloc(...)

for (i=...)
{
  if (x != 0)
    t1 = x;
  else
    t1 = 0;

  t1[i] = yyy;
}

which gets optimized to 

 x = malloc(...)

for (i=...)
{
  if (x != 0)
    t1 = x;
  else
    t1 = x; // NOTE REG_EQUAL (0);

  t1[i] = yyy;
}

which is further transformed to 

x = malloc
t1 = x;  //Note REG_EQUAL (0);
for (i=...)
{
  t1[i] = yyy;
}

I've attached the following files.
foo.c: Source code that shows the problem -- look for
compressed_min_issue_delay_vect.
foo.s: Generated assembly, with annotated instruction that is invalid
foo.c.139r.loop2_invariant: which shows the hoisting of the invariant.

This regression is caused by the fix to PR rtl-optimization/31360


-- 
           Summary: [4.3 regression] Invalid loop optimization causes
                    bootstrap failure in genautomata
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rearnsha at gcc dot gnu dot org
GCC target triplet: arm-netbsdelf2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31848