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Bug 1413096 - Replace ffs with MathAlgorithms functions. r=njn

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- In the cases where it's used on powers of 2, replace it with
  FloorLog2() + 1.
- In the cases where it's used on any kind of number, replace it with
  CountTrailingZeroes, which is `ffs(x) - 1`.
- In the case of tiny allocations in arena_t::MallocSmall, we rearrange
  the code so that the intent is clearer, which also simplifies the
  expression for the mBins offset: mBins[0] is the first tiny bucket,
  for allocations of sizes 1 << TINY_MIN_2POW, mBins[1] for allocations
  of size 1 << (TINY_MIN_2POW + 1), etc. up to small_min. So the offset
  is really the log2 of the normalized size.

--HG--
extra : rebase_source : 954a655dcaa93857dc976078e133704bb141de0d
This commit is contained in:
Mike Hommey 2017-10-30 17:44:16 +09:00
parent 331ef2d1a6
commit 87e49e764d
1 changed files with 7 additions and 25 deletions
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32
memory/build/mozjemalloc.cpp
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@ -163,19 +163,6 @@ using namespace mozilla;
#define STDERR_FILENO 2
// Use MSVC intrinsics.
#pragma intrinsic(_BitScanForward)
static __forceinline int
ffs(int x)
{
unsigned long i;
if (_BitScanForward(&i, x) != 0) {
return i + 1;
}
return 0;
}
// Implement getenv without using malloc.
static char mozillaMallocOptionsBuf[64];
@ -230,9 +217,6 @@ typedef long ssize_t;
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#ifndef XP_DARWIN
#include <strings.h>
#endif
#include <unistd.h>
#ifdef XP_DARWIN
@ -2204,7 +2188,7 @@ arena_run_reg_alloc(arena_run_t* run, arena_bin_t* bin)
mask = run->regs_mask[i];
if (mask != 0) {
// Usable allocation found.
bit = ffs((int)mask) - 1;
bit = CountTrailingZeroes32(mask);
regind = ((i << (SIZEOF_INT_2POW + 3)) + bit);
MOZ_ASSERT(regind < bin->nregs);
@ -2222,7 +2206,7 @@ arena_run_reg_alloc(arena_run_t* run, arena_bin_t* bin)
mask = run->regs_mask[i];
if (mask != 0) {
// Usable allocation found.
bit = ffs((int)mask) - 1;
bit = CountTrailingZeroes32(mask);
regind = ((i << (SIZEOF_INT_2POW + 3)) + bit);
MOZ_ASSERT(regind < bin->nregs);
@ -2979,14 +2963,10 @@ arena_t::MallocSmall(size_t aSize, bool aZero)
if (aSize < small_min) {
// Tiny.
aSize = RoundUpPow2(aSize);
bin = &mBins[ffs((int)(aSize >> (TINY_MIN_2POW + 1)))];
// Bin calculation is always correct, but we may need
// to fix size for the purposes of assertions and/or
// stats accuracy.
if (aSize < (1U << TINY_MIN_2POW)) {
aSize = 1U << TINY_MIN_2POW;
}
bin = &mBins[FloorLog2(aSize >> TINY_MIN_2POW)];
} else if (aSize <= small_max) {
// Quantum-spaced.
aSize = QUANTUM_CEILING(aSize);
@ -2995,7 +2975,7 @@ arena_t::MallocSmall(size_t aSize, bool aZero)
// Sub-page.
aSize = RoundUpPow2(aSize);
bin = &mBins[ntbins + nqbins +
(ffs((int)(aSize >> SMALL_MAX_2POW_DEFAULT)) - 2)];
(FloorLog2(aSize >> SMALL_MAX_2POW_DEFAULT) - 1)];
}
MOZ_DIAGNOSTIC_ASSERT(aSize == bin->reg_size);
@ -4120,7 +4100,9 @@ static
#else
pagesize = (size_t)result;
pagesize_mask = (size_t)result - 1;
pagesize_2pow = ffs((int)result) - 1;
pagesize_2pow = FloorLog2(result);
MOZ_RELEASE_ASSERT(1ULL << pagesize_2pow == pagesize,
"Page size is not a power of two");
#endif
// Get runtime configuration.