hakmem/core/box/tiny_legacy_fallback_box.h

#ifndef HAKMEM_TINY_LEGACY_FALLBACK_BOX_H
#define HAKMEM_TINY_LEGACY_FALLBACK_BOX_H

#include <stdbool.h>
#include <stdint.h>
#include "../front/tiny_unified_cache.h"
#include "../front/tiny_first_page_cache.h"  // Phase 3 C2: First page inline cache
#include "../hakmem.h"
#include "tiny_front_v3_env_box.h"
#include "free_path_stats_box.h"
#include "tiny_front_hot_box.h"
#include "tiny_metadata_cache_env_box.h"  // Phase 3 C2: Metadata cache ENV gate
#include "hakmem_env_snapshot_box.h"  // Phase 4 E1: ENV snapshot consolidation
#include "tiny_unified_cache_fastapi_env_box.h"  // Phase 74-3: FASTAPI ENV gate
#include "tiny_c6_inline_slots_env_box.h" // Phase 75-1: C6 inline slots ENV gate
#include "../front/tiny_c6_inline_slots.h" // Phase 75-1: C6 inline slots API
#include "tiny_c5_inline_slots_env_box.h" // Phase 75-2: C5 inline slots ENV gate
#include "../front/tiny_c5_inline_slots.h" // Phase 75-2: C5 inline slots API

// Purpose: Encapsulate legacy free logic (shared by multiple paths)
// Called by: malloc_tiny_fast.h (free path) + tiny_c6_ultra_free_box.c (C6 fallback)
//
// Contract:
//   - base: BASE pointer (already extracted via ptr - 1)
//   - class_idx: size class (0-7)
//   - Returns: void (always succeeds or falls back to tiny_hot_free_fast)
//
__attribute__((always_inline))
static inline void tiny_legacy_fallback_free_base_with_env(void* base, uint32_t class_idx, const HakmemEnvSnapshot* env) {
    // Phase 75-2: C5 Inline Slots early-exit (ENV gated)
    // Try C5 inline slots FIRST (before C6 and unified cache) for class 5
    if (class_idx == 5 && tiny_c5_inline_slots_enabled()) {
        if (c5_inline_push(c5_inline_tls(), base)) {
            // Success: pushed to C5 inline slots
            FREE_PATH_STAT_INC(legacy_fallback);
            if (__builtin_expect(free_path_stats_enabled(), 0)) {
                g_free_path_stats.legacy_by_class[class_idx]++;
            }
            return;
        }
        // FULL → fall through to C6/unified cache
    }

    // Phase 75-1: C6 Inline Slots early-exit (ENV gated)
    // Try C6 inline slots SECOND (before unified cache) for class 6
    if (class_idx == 6 && tiny_c6_inline_slots_enabled()) {
        if (c6_inline_push(c6_inline_tls(), base)) {
            // Success: pushed to C6 inline slots
            FREE_PATH_STAT_INC(legacy_fallback);
            if (__builtin_expect(free_path_stats_enabled(), 0)) {
                g_free_path_stats.legacy_by_class[class_idx]++;
            }
            return;
        }
        // FULL → fall through to unified cache
    }

    const TinyFrontV3Snapshot* front_snap =
        env ? (env->tiny_front_v3_enabled ? tiny_front_v3_snapshot_get() : NULL)
            : (__builtin_expect(tiny_front_v3_enabled(), 0) ? tiny_front_v3_snapshot_get() : NULL);
    const bool metadata_cache_on = env ? env->tiny_metadata_cache_eff : tiny_metadata_cache_enabled();

    // Phase 3 C2 Patch 2: First page cache hint (optional fast-path)
    // Check if pointer is in cached page (avoids metadata lookup in future optimizations)
    if (__builtin_expect(metadata_cache_on, 0)) {
        // Note: This is a hint-only check. Even if it hits, we still use the standard path.
        // The cache will be populated during refill operations for future use.
        // Currently this just validates the cache state; actual optimization TBD.
        if (tiny_first_page_cache_hit(class_idx, base, 4096)) {
            // Future: could optimize metadata access here
        }
    }

    // Legacy fallback - Unified Cache push
    if (!front_snap || front_snap->unified_cache_on) {
        // Phase 74-3 (P0): FASTAPI path (ENV-gated)
        if (tiny_uc_fastapi_enabled()) {
            // Preconditions guaranteed:
            // - unified_cache_on == true (checked above)
            // - TLS init guaranteed by front_gate_unified_enabled() in malloc_tiny_fast.h
            // - Stats compiled-out in FAST builds
            if (unified_cache_push_fast(class_idx, HAK_BASE_FROM_RAW(base))) {
                FREE_PATH_STAT_INC(legacy_fallback);

                // Per-class breakdown (Phase 4-1)
                if (__builtin_expect(free_path_stats_enabled(), 0)) {
                    if (class_idx < 8) {
                        g_free_path_stats.legacy_by_class[class_idx]++;
                    }
                }
                return;
            }
            // FULL → fallback to slow path (rare)
        }

        // Original path (FASTAPI=0 or fallback)
        if (unified_cache_push(class_idx, HAK_BASE_FROM_RAW(base))) {
            FREE_PATH_STAT_INC(legacy_fallback);

            // Per-class breakdown (Phase 4-1)
            if (__builtin_expect(free_path_stats_enabled(), 0)) {
                if (class_idx < 8) {
                    g_free_path_stats.legacy_by_class[class_idx]++;
                }
            }
            return;
        }
    }

    // Final fallback
    tiny_hot_free_fast(class_idx, base);
}

__attribute__((always_inline))
static inline void tiny_legacy_fallback_free_base(void* base, uint32_t class_idx) {
    const HakmemEnvSnapshot* env = hakmem_env_snapshot_enabled() ? hakmem_env_snapshot() : NULL;
    tiny_legacy_fallback_free_base_with_env(base, class_idx, env);
}

#endif // HAKMEM_TINY_LEGACY_FALLBACK_BOX_H