[Mesa-dev] [PATCH] nir: fix divide by zero crash during constant folding

[Timothy Arceri]

On 28/02/18 14:13, Jason Ekstrand wrote:
> On February 27, 2018 19:11:49 Jason Ekstrand <jason at jlekstrand.net> wrote:
> 
>> On February 27, 2018 19:07:43 Timothy Arceri <tarceri at itsqueeze.com> 
>> wrote:
>>
>>> From the GLSL 4.60 spec Section 5.9 (Expressions):
>>>
>>>    "Dividing by zero does not cause an exception but does result in
>>>     an unspecified value."
>>>
>>> Fixes: 89285e4d47a6 "nir: add new constant folding infrastructure"
>>>
>>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105271
>>> ---
>>>  src/compiler/nir/nir_opcodes.py | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/src/compiler/nir/nir_opcodes.py 
>>> b/src/compiler/nir/nir_opcodes.py
>>> index 278562b2bd..dcc5b07d05 100644
>>> --- a/src/compiler/nir/nir_opcodes.py
>>> +++ b/src/compiler/nir/nir_opcodes.py
>>> @@ -403,9 +403,9 @@ binop("imul_high", tint32, commutative,
>>>  binop("umul_high", tuint32, commutative,
>>>        "(uint32_t)(((uint64_t) src0 * (uint64_t) src1) >> 32)")
>>>
>>> -binop("fdiv", tfloat, "", "src0 / src1")
>>> -binop("idiv", tint, "", "src0 / src1")
>>> -binop("udiv", tuint, "", "src0 / src1")
>>> +binop("fdiv", tfloat, "", "src1 == 0 ? 0 : (src0 / src1)")
>>
>> Should this return inf?
> 
> Or maybe an unsignaling NaN?  I'm not really sure.

I'm not sure. GLSL IR doesn't even try to catch this currently.

> 
>>> +binop("idiv", tint, "", "src1 == 0 ? 0 : (src0 / src1)")
>>> +binop("udiv", tuint, "", "src1 == 0 ? 0 : (src0 / src1)")
>>>
>>>  # returns a boolean representing the carry resulting from the 
>>> addition of
>>>  # the two unsigned arguments.
>>> -- 
>>> 2.14.3
>>>
>>> _______________________________________________
>>> mesa-dev mailing list
>>> mesa-dev at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
>>
> 
>