http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49618
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ebotcazou at gcc dot
| |gnu.org, jakub at gcc dot
| |gnu.org, rsandifo at gcc
| |dot gnu.org
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-07-04
08:10:19 UTC ---
I think the problem is either that the MEM has the MEM_NOTRAP_P flag set on it:
(mem/f/i:SI (symbol_ref/i:SI ("__dso_handle") <var_decl 0x7ffff13ce320
__dso_handle>) [0 S4 A32])
That makes ifcvt believe it can try to use a conditional move with that as an
operand, and as there is no conditional move with MEM operand on this target,
it is forced into register first.
MEM_NOTRAP_P is set in set_mem_attributes_minus_bitpos:
/* Note whether this expression can trap. */
MEM_NOTRAP_P (ref) = !tree_could_trap_p (t);
where t is VAR_DECL for __dso_handle with DECL_WEAK.
Or the problem might be that noce_try_cmove_arith should be using
else if (may_trap_or_fault_p (a) || may_trap_or_fault_p (b))
return FALSE;
instead of
else if (may_trap_p (a) || may_trap_p (b))
return FALSE;
Eric/Richard, what do you think? The comments seem to be fuzzy to me, some
comments say that MEM_NOTRAP_P only apply to the position where the MEM is
originally used (and in this case the __dso_handle var is read only guarded
with if (__dso_handle != NULL), on the other side I wonder if we ever clear
MEM_NOTRAP_P on unguarded DECL_WEAK var references.
