Mutex Relation

The mutually exclusive (mutex) relation indicates that not more than one predicate in a group of predicates can be true simultaneously.

In the following example, if predicates p1, p2 and p3 are mutex, there is no write-after-write dependency violation because only one of these instructions actually executes.

(p1) mov r4 = 2

(p2) mov r4 = 5

(p3) mov r4 = 7

IAS creates mutex relations in the following cases:

• non-predicated regular compare instructions

  In the following code, the predicates p1 and p2 are mutex only when the qualifying
  predicate (qp) is p0.

  (qp) cmp.eq p1, p2 = r1, r2

  Regular compare instructions include all the instructions that write to a pair of predicates:
  cmp, fcmp, tbit, and tnat. Parallel compare and compare unconditional instructions do
  not belong in this category.

• unconditional compare instructions

  In the following code, the predicates p1 and p2 are mutex (regardless of the qualifying
  predicate value).

  (p3) cmp.eq.unc p1, p2 = r1, r2

• relation definition “mutex“

  In the following code, the user annotation pred.rel sets mutex relations between predicates
  p1, p2, and p3:

  .pred.rel “mutex“, p1, p2, p3