On 08/28/2017 12:26 PM, Tom de Vries wrote:
> Hi,
>
> I think I found a bug in r17465:
> ...
>> * cse.c (simplify_ternary_operation): Handle more IF_THEN_ELSE
>> simplifications.
>>
>> diff --git a/gcc/cse.c b/gcc/cse.c
>> index e001597..3c27387 100644
>> --- a/gcc/cse.c
>> +++ b/gcc/cse.c
>> @@ -4713,6 +4713,17 @@ simplify_ternary_operation (code, mode,
>> op0_mode, op0, op1, op2)
>
> Note: the parameters of simplify_ternary_operation have the following
> meaning:
> ...
> /* Simplify CODE, an operation with result mode MODE and three operands,
> OP0, OP1, and OP2. OP0_MODE was the mode of OP0 before it became
> a constant. Return 0 if no simplifications is possible. */
>
> rtx
> simplify_ternary_operation (code, mode, op0_mode, op0, op1, op2)
> enum rtx_code code;
> enum machine_mode mode, op0_mode;
> rtx op0, op1, op2;
> ...
>
>> && rtx_equal_p (XEXP (op0, 1), op1)
>> && rtx_equal_p (XEXP (op0, 0), op2))
>> return op2;
>> + else if (! side_effects_p (op0))
>> + {
>> + rtx temp;
>> + temp = simplify_relational_operation (GET_CODE (op0), op0_mode,
>> + XEXP (op0, 0), XEXP
>> (op0, 1));
>
> We're handling code == IF_THEN_ELSE here, so op0 is the condition, op1
> is the 'then expr' and op2 is the 'else expr'.
>
> The parameters of simplify_relational_operation have the following meaning:
> ...
> /* Like simplify_binary_operation except used for relational operators.
> MODE is the mode of the operands, not that of the result. If MODE
> is VOIDmode, both operands must also be VOIDmode and we compare the
> operands in "infinite precision".
>
> If no simplification is possible, this function returns zero.
> Otherwise, it returns either const_true_rtx or const0_rtx. */
>
> rtx
> simplify_relational_operation (code, mode, op0, op1)
> enum rtx_code code;
> enum machine_mode mode;
> rtx op0, op1;
> ...
>
> The problem in the patch is that we use op0_mode argument for the mode
> parameter. The mode parameter of simplify_relational_operation needs to
> be the mode of the operands of the condition, while op0_mode is the mode
> of the condition.
>
> Patch below fixes this on current trunk.
>
> [ I found this by running into an ICE in
> gcc.c-torture/compile/pr28776-2.c for gcn target. I haven't been able to
> reproduce this with an upstream branch yet. ]
>
> OK for trunk if bootstrap and reg-test for x86_64 succeeds?
So clearly setting cmp_mode to op0_mode is wrong. But we also have to
make sure that if cmp_mode is VOIDmode that either XEXP (op0, 0) has a
non-void mode or that XEXP (op0, 1) has a non-void mode, otherwise we're
likely to abort down in simplify_const_relational_operation.
ISTM a better fix is to return NULL_RTX if cmp_mode is VOIDmode and both
the sub-operations are VOIDmode as well.
Can you try that and verify that pr28776-2.c continues to work?
jeff
