Re: [PATCH] Checking undefined_p before using the vr

[Jiufu Guo <guojiufu@linux.ibm.com>]

Hi,

Richard Biener <rguenther@suse.de> writes:

> On Thu, 7 Sep 2023, Jiufu Guo wrote:
>
>> Hi,
>> 
>> As discussed in PR111303:
>> 
>> For pattern "(X + C) / N": "div (plus@3 @0 INTEGER_CST@1) INTEGER_CST@2)",
>> Even if "X" has value-range and "X + C" does not overflow, "@3" may still
>> be undefined. Like below example:
>> 
>> _3 = _2 + -5;
>> if (0 != 0)
>>   goto <bb 3>; [34.00%]
>> else
>>   goto <bb 4>; [66.00%]
>> ;;  succ:       3
>> ;;              4
>> 
>> ;; basic block 3, loop depth 0
>> ;;  pred:       2
>> _5 = _3 / 5; 
>> ;;  succ:       4
>> 
>> The whole pattern "(_2 + -5 ) / 5" is in "bb 3", but "bb 3" would be
>> unreachable (because "if (0 != 0)" is always false).
>> And "get_range_query (cfun)->range_of_expr (vr3, @3)" is checked in
>> "bb 3", "range_of_expr" gets an "undefined vr3". Where "@3" is "_5".
>> 
>> So, before using "vr3", it would be safe to check "!vr3.undefined_p ()".
>> 
>> Bootstrap & regtest pass on ppc64{,le} and x86_64.
>> Is this ok for trunk?
>
> OK, but I wonder why ->range_of_expr () doesn't return false for
> undefined_p ()?  While "undefined" technically means we can treat
> it as nonnegative_p (or not, maybe but maybe not both), we seem to
> not want to do that.  So why expose it at all to ranger users
> (yes, internally we in some places want to handle undefined).

I guess, currently, it returns true and then lets the user check
undefined_p, maybe because it tries to only return false if the
type of EXPR is unsupported.

Let "range_of_expr" return false for undefined_p would save checking
undefined_p again when using the APIs.

Committed va r14-3913.

BR,
Jeff (Jiufu Guo)

>
> Richard.
>
>> BR,
>> Jeff (Jiufu Guo)
>> 
>> 	PR middle-end/111303
>> 
>> gcc/ChangeLog:
>> 
>> 	* match.pd ((X - N * M) / N): Add undefined_p checking.
>> 	(X + N * M) / N): Likewise.
>> 	((X + C) div_rshift N): Likewise.
>> 
>> gcc/testsuite/ChangeLog:
>> 
>> 	* gcc.dg/pr111303.c: New test.
>> 
>> ---
>>  gcc/match.pd                    |  3 +++
>>  gcc/testsuite/gcc.dg/pr111303.c | 11 +++++++++++
>>  2 files changed, 14 insertions(+)
>>  create mode 100644 gcc/testsuite/gcc.dg/pr111303.c
>> 
>> diff --git a/gcc/match.pd b/gcc/match.pd
>> index 801edb128f9..e2583ca7960 100644
>> --- a/gcc/match.pd
>> +++ b/gcc/match.pd
>> @@ -975,6 +975,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>>         /* "X+(N*M)" doesn't overflow.  */
>>         && range_op_handler (PLUS_EXPR).overflow_free_p (vr0, vr3)
>>         && get_range_query (cfun)->range_of_expr (vr4, @4)
>> +       && !vr4.undefined_p ()
>>         /* "X+N*M" is not with opposite sign as "X".  */
>>         && (TYPE_UNSIGNED (type)
>>  	   || (vr0.nonnegative_p () && vr4.nonnegative_p ())
>> @@ -995,6 +996,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>>         /* "X - (N*M)" doesn't overflow.  */
>>         && range_op_handler (MINUS_EXPR).overflow_free_p (vr0, vr3)
>>         && get_range_query (cfun)->range_of_expr (vr4, @4)
>> +       && !vr4.undefined_p ()
>>         /* "X-N*M" is not with opposite sign as "X".  */
>>         && (TYPE_UNSIGNED (type)
>>  	   || (vr0.nonnegative_p () && vr4.nonnegative_p ())
>> @@ -1025,6 +1027,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>>  	  /* "X+C" doesn't overflow.  */
>>  	  && range_op_handler (PLUS_EXPR).overflow_free_p (vr0, vr1)
>>  	  && get_range_query (cfun)->range_of_expr (vr3, @3)
>> +	  && !vr3.undefined_p ()
>>  	  /* "X+C" and "X" are not of opposite sign.  */
>>  	  && (TYPE_UNSIGNED (type)
>>  	      || (vr0.nonnegative_p () && vr3.nonnegative_p ())
>> diff --git a/gcc/testsuite/gcc.dg/pr111303.c b/gcc/testsuite/gcc.dg/pr111303.c
>> new file mode 100644
>> index 00000000000..eaabe55c105
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr111303.c
>> @@ -0,0 +1,11 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2" } */
>> +
>> +/* Make sure no ICE. */
>> +unsigned char a;
>> +int b(int c) {
>> +  if (c >= 5000)
>> +    return c / 5;
>> +}
>> +void d() { b(a - 5); }
>> +int main() {}
>>