i965: Don't consider null dst instructions as matching non-null dst.
When performing common subexpression elimination on instructions with non-null destinations we emit a MOV to copy the result to a new register that must have no other uses. In the case of: cmp.g.f0.0(8) null:D, vgrf43:F, 0.500000f ... cmp.g.f0.0(8) vgrf113:D, vgrf43:F, 0.500000f we put the first instruction in the AEB and decided that we could reuse its result when we found the second. Unfortunately, that meant that we'd emit a MOV from the first's destination, which is null. Don't do anything if the entry's destination is null and the instruction's destination is non-null. Tested-by: Tapani Pälli <email@example.com>
Showing with 4 additions and 2 deletions