LATX: extend EFLAGS reduction across TU calls and native patterns

[LaurenIsACoder]

Summary

• analyze EFLAGS requirements through bounded, analysis-only direct-call callee graphs and normal near returns
• propagate the resulting direct-call liveness through the full TU fixed point, including predecessor TBs
• let flag reduction consume native pattern metadata for CMP, TEST, BT, SUB, SHR, AND, floating-point Jcc, SETcc, CMOVcc, SBB, and NEG patterns
• keep indirect edges, missing successors, cross-page callees, locked fallbacks, zero-count shifts, and shared RET code conservative

Design

LATX_EFLAGS_CROSS=0 keeps the existing behavior and LATX_EFLAGS_CROSS=1 enables the direct-call analysis. Callee decoding is bounded and analysis-only: temporary TBs do not enter the execution TU, HBR input, AOT TB set, thunk table, or translation metrics.

The direct-call model assumes the normal ABI discipline that a near RET returns through the slot created by its matching direct CALL. Unknown and indirect control flow still requires all flags. Cross-page callees are intentionally excluded until AOT/SMC can record caller-to-callee page invalidation dependencies.

Pattern discovery runs before flag reduction. A consumer removes only the architectural EFLAGS reads replaced by its native translation; later consumers still preserve the corresponding producer flags. Locked memory operations and masked-zero shifts retain their ordinary EFLAGS paths.

Validation

• rebased on origin/master at d58864a036f
• LoongArch release x86_64 build: PASS
• LoongArch i386 build: PASS
• 54 focused native-pattern EFLAGS cases: PASS
• direct-call cross-boundary modes 0 and 1, cold and hot AOT: PASS
• SPEC CPU2000 integer train, cold AOT generation: 12/12 PASS
• SPEC CPU2000 integer train, hot AOT execution with cache mapping verified: 12/12 PASS
• 12 SPEC integer AOT files reduced by 194,760 bytes (0.599%) versus the prior pattern candidate

Runtime movement was sensitive to AOT code layout in individual benchmarks, so this PR claims the verified EFLAGS/code-size reduction and leaves layout tuning to a separate follow-up.