search for: nondet

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2020 Oct 08
2
Undef and Poison round table follow-up & a plan
...Store forwarding isn’t free; needs insertion of freeze (store x, p; v = load freeze p => store x, p; v = freeze x) (3) The third case is the value of struct/union padding. Padding is filled with unspecified value in C, so it is too undefined to use poison. We can fill it with defined bits nondeterministically chosen at allocation time (freeze poison). ``` <C> struct { char a; // 3 bytes padding int b; } s; v = s.b; => <IR> s = alloca {i8, i32} // alloca initializes bytes in a type-dependent manner // s[0], s[4~7]: poison // s[1~3]: let's fill these bytes with non...
2020 Oct 08
2
Undef and Poison round table follow-up & a plan
> It is important to note that this applies to trap representations and not to unspecified values. A structure or union never has a trap representation. Yes, nondeterministic bits would work for padding of struct/union, as described in (3) The third case is the value of struct/union padding. For the members of struct/union, it is allowed to have trap representation, so poison can be used. Juneyoung On Fri, Oct 9, 2020 at 5:37 AM Hubert Tong <hubert.reinte...
2020 Oct 09
2
Undef and Poison round table follow-up & a plan
...t; On Thu, Oct 8, 2020 at 7:13 PM Juneyoung Lee <juneyoung.lee at sf.snu.ac.kr> > wrote: > >> > It is important to note that this applies to trap representations and >> not to unspecified values. A structure or union never has a trap >> representation. >> Yes, nondeterministic bits would work for padding of struct/union, as >> described in (3) The third case is the value of struct/union padding. >> For the members of struct/union, it is allowed to have trap >> representation, so poison can be used. >> > At what point are the members c...
2020 Oct 09
2
Undef and Poison round table follow-up & a plan
...<juneyoung.lee at sf.snu.ac.kr> >>> wrote: >>> >>>> > It is important to note that this applies to trap representations and >>>> not to unspecified values. A structure or union never has a trap >>>> representation. >>>> Yes, nondeterministic bits would work for padding of struct/union, as >>>> described in (3) The third case is the value of struct/union padding. >>>> For the members of struct/union, it is allowed to have trap >>>> representation, so poison can be used. >>>> >...
2020 Oct 10
2
Undef and Poison round table follow-up & a plan
....ac.kr> wrote: >>>>> >>>>>> > It is important to note that this applies to trap representations >>>>>> and not to unspecified values. A structure or union never has a trap >>>>>> representation. >>>>>> Yes, nondeterministic bits would work for padding of struct/union, as >>>>>> described in (3) The third case is the value of struct/union padding. >>>>>> For the members of struct/union, it is allowed to have trap >>>>>> representation, so poison can be use...