Hi Jeff
On 09/01/18 23:43, Jeff Law wrote:
On 01/05/2018 12:25 PM, Sudakshina Das wrote:
Hi Jeff
On 05/01/18 18:44, Jeff Law wrote:
On 01/04/2018 08:35 AM, Sudakshina Das wrote:
Hi
The bug reported a particular test di-longlong64-sync-1.c failing when
run on arm-linux-gnueabi with options -mthumb -march=armv5t -O[g,1,2,3]
and -mthumb -march=armv6 -O[g,1,2,3].
According to what I could see, the crash was caused because of the
explicit VOIDmode argument that was sent to emit_store_flag_force ().
Since the comparing argument was a long long, it was being forced into a
VOID type register before the comparison (in prepare_cmp_insn()) is done.
As pointed out by Kyrill, there is a comment on emit_store_flag() which
says "MODE is the mode to use for OP0 and OP1 should they be CONST_INTs.
If it is VOIDmode, they cannot both be CONST_INT". This condition is
not true in this case and thus I think it is suitable to change the
argument.
Testing done: Checked for regressions on bootstrapped
arm-none-linux-gnueabi and arm-none-linux-gnueabihf and added new test
cases.
Sudi
ChangeLog entries:
*** gcc/ChangeLog ***
2017-01-04 Sudakshina Das <sudi....@arm.com>
PR target/82096
* optabs.c (expand_atomic_compare_and_swap): Change argument
to emit_store_flag_force.
*** gcc/testsuite/ChangeLog ***
2017-01-04 Sudakshina Das <sudi....@arm.com>
PR target/82096
* gcc.c-torture/compile/pr82096-1.c: New test.
* gcc.c-torture/compile/pr82096-2.c: Likwise.
In the case where both (op0/op1) to
emit_store_flag/emit_store_flag_force are constants, don't we know the
result of the comparison and shouldn't we have optimized the store flag
to something simpler?
I feel like I must be missing something here.
emit_store_flag_force () is comparing a register to op0.
?
/* Emit a store-flags instruction for comparison CODE on OP0 and OP1
and storing in TARGET. Normally return TARGET.
Return 0 if that cannot be done.
MODE is the mode to use for OP0 and OP1 should they be CONST_INTs. If
it is VOIDmode, they cannot both be CONST_INT.
So we're comparing op0 and op1 AFAICT. One, but not both can be a
CONST_INT. If both are a CONST_INT, then you need to address the
problem in the caller (by optimizing away the condition). If you've got
a REG and a CONST_INT, then the mode should be taken from the REG operand.
The 2 constant arguments are to the expand_atomic_compare_and_swap ()
function. emit_store_flag_force () is used in case when this function is
called by the bool variant of the built-in function where the bool
return value is computed by comparing the result register with the
expected op0.
So if only one of the two objects is a CONST_INT, then the mode should
come from the other object. I think that's the fundamental problem here
and that you're just papering over it by changing the caller.
I think my earlier explanation was a bit misleading and I may have
rushed into quoting the comment about both operands being const for
emit_store_flag_force(). The problem is with the function and I do agree
with your suggestion of changing the function to add the code below to
be a better approach than the changing the caller. I will change the
patch and test it.
Thanks
Sudi
For example in emit_store_flag_1 we have this code:
/* If one operand is constant, make it the second one. Only do this
if the other operand is not constant as well. */
if (swap_commutative_operands_p (op0, op1))
{
std::swap (op0, op1);
code = swap_condition (code);
}
if (mode == VOIDmode)
mode = GET_MODE (op0);
I think if you do this in emit_store_flag_force as well everything will
"just work".
You can put it after this call/test pair:
/* First see if emit_store_flag can do the job. */
tem = emit_store_flag (target, code, op0, op1, mode, unsignedp,
normalizep);
if (tem != 0)
return tem;
jeff
