diff options
Diffstat (limited to 'compiler/optimizing/parallel_move_resolver.h')
| -rw-r--r-- | compiler/optimizing/parallel_move_resolver.h | 18 |
1 files changed, 12 insertions, 6 deletions
diff --git a/compiler/optimizing/parallel_move_resolver.h b/compiler/optimizing/parallel_move_resolver.h index 173cffc71e..36ce575609 100644 --- a/compiler/optimizing/parallel_move_resolver.h +++ b/compiler/optimizing/parallel_move_resolver.h @@ -92,12 +92,18 @@ class ParallelMoveResolver : public ValueObject { // other moves to satisfy dependencies). // // Return whether another move in the dependency cycle needs to swap. This - // is to handle pair swaps, where we want the pair to swap first to avoid - // building pairs that are unexpected by the code generator. For example, if - // we were to swap R1 with R2, we would need to update all locations using - // R2 to R1. So a (R2,R3) pair register could become (R1,R3). We could make - // the code generator understand such pairs, but it's easier and cleaner to - // just not create such pairs and exchange pairs in priority. + // is to handle 64bits swaps: + // 1) In the case of register pairs, where we want the pair to swap first to avoid + // building pairs that are unexpected by the code generator. For example, if + // we were to swap R1 with R2, we would need to update all locations using + // R2 to R1. So a (R2,R3) pair register could become (R1,R3). We could make + // the code generator understand such pairs, but it's easier and cleaner to + // just not create such pairs and exchange pairs in priority. + // 2) Even when the architecture does not have pairs, we must handle 64bits swaps + // first. Consider the case: (R0->R1) (R1->S) (S->R0), where 'S' is a single + // stack slot. If we end up swapping S and R0, S will only contain the low bits + // of R0. If R0->R1 is for a 64bits instruction, R1 will therefore not contain + // the right value. MoveOperands* PerformMove(size_t index); DISALLOW_COPY_AND_ASSIGN(ParallelMoveResolver); |