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[Bug rtl-optimization/78580] [6/7 Regression] Segfault in gcc with multilib (-m32) and -ffixed-*


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78580

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |uros at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
/* PR rtl-optimization/78580 */
/* { dg-do compile } */
/* { dg-options "-O0 -ffixed-ebx" } */

extern const signed char a;

int
foo (signed char x)
{
  return x;
}

int
main ()
{
  foo (a);
  return 0;
}

Apparently with just -m32 we have ira_allocno_classes of:
AREG,DREG,CREG,BREG,SIREG,DIREG,AD_REGS,CLOBBERED_REGS,Q_REGS,NON_Q_REGS,TLS_GOTBASE_REGS,GENERAL_REGS,FP_TOP_REG,FP_SECOND_REG,FLOAT_REGS,FLOAT_INT_REGS
while with -m32 -ffixed-ebx
AREG,DREG,CREG,SIREG,DIREG,AD_REGS,CLOBBERED_REGS,NON_Q_REGS,TLS_GOTBASE_REGS,GENERAL_REGS,FP_TOP_REG,FP_SECOND_REG,FLOAT_REGS,FLOAT_INT_REGS
i.e. BREG and Q_REGS is missing in the latter case.  update_bad_spill_attribute
only initializes dead_points for the allocno classes, but then we process
allocno with Q_REGS allocno class and in the latter case (sometimes) ICE
because dead_points[Q_REGS] is random garbage.
So, is the bug that i?86 needs Q_REGS to be an allocno class always (shall
ix86_additional_allocno_class_p return true also for Q_REGS?  Just for -m32 or
always?), or is the bug that if Q_REGS is not an allocno class then there
shouldn't be allocno with that class?

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