[gen] add @before and @after predicates for relaxations in diy7

[ShaleXIONG]

Add diy7-only predicate syntax for relax inputs:

• @before(...)
• @after(...)

The parser entry points are split so predicate syntax is accepted only by diy7. The shared main/diyone7, diycross7, and cumul parsers reject predicate syntax.

During relax expansion, invalid predicate placement is filtered before search:

• @before(...) is only valid at the start of a relaxation sequence
• @after(...) is only valid at the end of a relaxation sequence
• predicates in the middle of a concrete composition are discarded

During diy7 cycle search, boundary predicates are checked against neighbouring concrete edges. Once checked, predicates are stripped before passing candidate cycles to the normal test generator.

Added tests for:

• diy7 parser acceptance of @before(...) and @after(...), while other parsers reject of predicate syntax
• filtering invalid predicate placement to []
• In diy7 cycle generation, the predicates @beforeand @after merge as expected

Example

diy7 -arch AArch64 -cycleonly true -size 4 -relax '[@before(Po) PodRW Rfe @after(Po)]' -safe Po

This constrains the generated boundary edges to match the predicates. Po will match @before(Po) and after(Po) during the searching.

Generator produced 2 tests
Relaxations tested: {[@before(PosRR),PodRW,Rfe,@after(PosRR)]} {[@before(PodRR),PodRW,Rfe,@after(PodRR)]}
LB000: PosRR PodRW Rfe PosRR PodRW Rfe
LB001: PodRR PodRW Rfe PodRR PodRW Rfe

Another example contains composite relax:

diy7 -arch AArch64 -cycleonly true -size 4 -relax '[PodRW Rfe @after([PodRW Rfe])]'

In this case, the only relaxation will be match with themselves, i.e., the leading PodRW Rfe matches the trailing @after([PodRW Rfe]).

Generator produced 3 tests
Relaxations tested: {[PodRW,Rfe,@after(PodRW),@after(Rfe)]}
LB000: PodRW Rfe PodRW Rfe
3.LB000: PodRW Rfe PodRW Rfe PodRW Rfe
4.LB000: PodRW Rfe PodRW Rfe PodRW Rfe PodRW Rfe