https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79619
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-02-20
CC| |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. GIMPLE DSE removes the store
# PT = null
_2 = MEM[(char * <address-space-1> *)0B];
*_2 = 1;
but not here:
# PT = null
_2 = MEM[(char * <address-space-1> *)0B];
*_2 = 1;
# PT = nonlocal escaped null
_4 = MEM[(char * <address-space-1> *)8B];
*_4 = 1;
because it thinks the value is eventually used by the following load from 8B.
'PT = null' addresses are thought to be not global memory.
-f[no-]delete-null-pointer-checks controls this globally for all address
spaces.
The following fixes the testcase, but it looks to me like all
flag_delete_null_pointer_checks tests in the middle end should be replaced
by this (or some wrapper so eventually the target can specify which
address-spaces
may have objects at address zero):
Index: gcc/tree-ssa-structalias.c
===================================================================
--- gcc/tree-ssa-structalias.c (revision 245594)
+++ gcc/tree-ssa-structalias.c (working copy)
@@ -3407,7 +3407,10 @@ get_constraint_for_1 (tree t, vec<ce_s>
|| (TREE_CODE (t) == CONSTRUCTOR
&& CONSTRUCTOR_NELTS (t) == 0))
{
- if (flag_delete_null_pointer_checks)
+ if (flag_delete_null_pointer_checks
+ && (! POINTER_TYPE_P (TREE_TYPE (t))
+ || (TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (t)))
+ == ADDR_SPACE_GENERIC)))
temp.var = nothing_id;
else
temp.var = nonlocal_id;
accordingly the documentation of -fdelete-null-pointer-checks should be
adjusted to say it only affects the generic address space.
