Hi,
gcc.dg/atomic/c11-atomic-exec-1.c has been failing at -O2 -mcpu=v8 on SPARC
since the fix for PR middle-end/61268 was installed, i.e. with all 5.x, 6.x
and 7.0 compilers. The failure mode is as follows:
emit_cstore is called on:
(mem/c:DF (plus:SI (plus:SI (reg/f:SI 104 virtual-stack-vars)
(reg:SI 1753))
(const_int 8 [0x8])) [2 D.1567+8 S8 A64])
and does:
last = get_last_insn ();
then it calls prepare_operand, which calls copy_to_mode_reg, which calls
emit_move_insn, which calls validize_mem, which modifies the MEM in-place:
(mem/c:DF (plus:SI (reg/f:SI 1757)
(const_int 8 [0x8])) [2 D.1567+8 S8 A64])
after emitting an addition:
(set (reg/f:SI 1757)
(plus:SI (reg/f:SI 104 virtual-stack-vars) (reg:SI 1753)))
But the call to maybe_expand_insn from emit_cstore fails so:
delete_insns_since (last);
is invoked and the addition is lost, i.e. (reg/f:SI 1757) will be emitted
uninitialized in the RTL stream, leading to a SIGSEGV at run time.
IMO this shows that the explow.c hunk of the fix for PR middle-end/61268 was
ill-advised and should not have been accepted. Having copy_to_mode_reg or
emit_move_insn silently modify their argument is IMO a recipe for problems.
So the attached patch backs it out and I suggest installing on all branches.
Tested on x86_64-suse-linux.
2016-10-15 Eric Botcazou
* explow.c (validize_mem): Do not modify the argument in-place.
--
Eric BotcazouIndex: explow.c
===
--- explow.c (revision 241147)
+++ explow.c (working copy)
@@ -496,9 +496,8 @@ memory_address_addr_space (machine_mode
return x;
}
-/* If REF is a MEM with an invalid address, change it into a valid address.
- Pass through anything else unchanged. REF must be an unshared rtx and
- the function may modify it in-place. */
+/* Convert a mem ref into one with a valid memory address.
+ Pass through anything else unchanged. */
rtx
validize_mem (rtx ref)
@@ -510,7 +509,8 @@ validize_mem (rtx ref)
MEM_ADDR_SPACE (ref)))
return ref;
- return replace_equiv_address (ref, XEXP (ref, 0), true);
+ /* Don't alter REF itself, since that is probably a stack slot. */
+ return replace_equiv_address (ref, XEXP (ref, 0));
}
/* If X is a memory reference to a member of an object block, try rewriting
