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Make heap large chunk bit twiddling branchless #4526

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merged 2 commits into from
Oct 15, 2024
Merged

Make heap large chunk bit twiddling branchless #4526

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731f2c3
Make heap large chunk bit twiddling branchless
dipinhora Oct 9, 2024
6a660c9
use `#define` preprocessor macros
dipinhora Oct 15, 2024
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24 changes: 18 additions & 6 deletions src/libponyrt/mem/heap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -46,9 +46,12 @@ typedef struct small_chunk_t
#define SMALL_CHUNK_SIZECLASS_BITMASK (uintptr_t)0x1C
// TODO: figure out how to calculate the `2` from `SMALL_CHUNK_SIZECLASS_BITMASK` at compile time
#define SMALL_CHUNK_SIZECLASS_SHIFT (uintptr_t)2
#define LARGE_CHUNK_SLOT_BITMASK (uintptr_t)0x4
#define LARGE_CHUNK_SHALLOW_BITMASK (uintptr_t)0x8
#define LARGE_CHUNK_FINALISER_BITMASK (uintptr_t)0x10
#define LARGE_CHUNK_SLOT_BITMASK_SHIFT_AMOUNT (uintptr_t)2
#define LARGE_CHUNK_SLOT_BITMASK ((uintptr_t)0x1 << LARGE_CHUNK_SLOT_BITMASK_SHIFT_AMOUNT)
#define LARGE_CHUNK_SHALLOW_BITMASK_SHIFT_AMOUNT (uintptr_t)3
#define LARGE_CHUNK_SHALLOW_BITMASK ((uintptr_t)0x1 << LARGE_CHUNK_SHALLOW_BITMASK_SHIFT_AMOUNT)
#define LARGE_CHUNK_FINALISER_BITMASK_SHIFT_AMOUNT (uintptr_t)4
#define LARGE_CHUNK_FINALISER_BITMASK ((uintptr_t)0x1 << LARGE_CHUNK_FINALISER_BITMASK_SHIFT_AMOUNT)
#define CHUNK_M_BITMASK ~(CHUNK_TYPE_BITMASK | CHUNK_NEEDS_TO_BE_CLEARED_BITMASK | SMALL_CHUNK_SIZECLASS_BITMASK | LARGE_CHUNK_SLOT_BITMASK | LARGE_CHUNK_SHALLOW_BITMASK | LARGE_CHUNK_FINALISER_BITMASK)

enum
Expand Down Expand Up @@ -172,7 +175,10 @@ static void set_large_chunk_slot(large_chunk_t* chunk, uint32_t slot)
{
// `!!` to normalize to 1 or 0
slot = !!slot;
((chunk_t*)chunk)->m = (char*)(((uintptr_t)((chunk_t*)chunk)->m & ~LARGE_CHUNK_SLOT_BITMASK) | (slot == 1 ? LARGE_CHUNK_SLOT_BITMASK : 0));
// left shift size to get bits in the right spot for OR'ing into `chunk->m`
slot = slot << LARGE_CHUNK_SLOT_BITMASK_SHIFT_AMOUNT;
pony_assert(slot == LARGE_CHUNK_SLOT_BITMASK || slot == 0);
((chunk_t*)chunk)->m = (char*)(((uintptr_t)((chunk_t*)chunk)->m & ~LARGE_CHUNK_SLOT_BITMASK) | slot);
}

static uint32_t get_large_chunk_shallow(large_chunk_t* chunk)
Expand All @@ -185,7 +191,10 @@ static void set_large_chunk_shallow(large_chunk_t* chunk, uint32_t shallow)
{
// `!!` to normalize to 1 or 0
shallow = !!shallow;
((chunk_t*)chunk)->m = (char*)(((uintptr_t)((chunk_t*)chunk)->m & ~LARGE_CHUNK_SHALLOW_BITMASK) | (shallow == 1 ? LARGE_CHUNK_SHALLOW_BITMASK : 0));
// left shift size to get bits in the right spot for OR'ing into `chunk->m`
shallow = shallow << LARGE_CHUNK_SHALLOW_BITMASK_SHIFT_AMOUNT;
pony_assert(shallow == LARGE_CHUNK_SHALLOW_BITMASK || shallow == 0);
((chunk_t*)chunk)->m = (char*)(((uintptr_t)((chunk_t*)chunk)->m & ~LARGE_CHUNK_SHALLOW_BITMASK) | shallow);
}

static uint32_t get_large_chunk_finaliser(large_chunk_t* chunk)
Expand All @@ -198,7 +207,10 @@ static void set_large_chunk_finaliser(large_chunk_t* chunk, uint32_t finaliser)
{
// `!!` to normalize to 1 or 0
finaliser = !!finaliser;
((chunk_t*)chunk)->m = (char*)(((uintptr_t)((chunk_t*)chunk)->m & ~LARGE_CHUNK_FINALISER_BITMASK) | (finaliser == 1 ? LARGE_CHUNK_FINALISER_BITMASK : 0));
// left shift size to get bits in the right spot for OR'ing into `chunk->m`
finaliser = finaliser << LARGE_CHUNK_FINALISER_BITMASK_SHIFT_AMOUNT;
pony_assert(finaliser == LARGE_CHUNK_FINALISER_BITMASK || finaliser == 0);
((chunk_t*)chunk)->m = (char*)(((uintptr_t)((chunk_t*)chunk)->m & ~LARGE_CHUNK_FINALISER_BITMASK) | finaliser);
}

static size_t get_small_chunk_size(small_chunk_t* chunk)
Expand Down
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