Function `zend_hash_find_bucket` consumes much time in WordPress workload

Description

Dear, maintainers:
I am utilizing PHP-FPM and have profiled performance data for a WordPress workload. Within this benchmark, I've identified certain hotspots. The performance analysis from 'perf' highlights that functions such as zend_hash_find and zend_hash_find_known_hash are consuming a considerable amount of time. Upon investigation, I suspect that the core issue lies within the zend_hash_find_bucket function.

Upon inspecting the assembly code and annotating it, I noticed that certain 'mov' instructions are causing significant delays. To address this, I attempted to optimize the zend_hash_find_bucket function. I experimented with optimizations such as utilizing prefetch instructions and employing struct alignment. However, these optimizations did not seem to have a discernible impact on performance.

Percent│
       │
       │
       │    Disassembly of section .text:
       │
       │    0000000000532ae0 <zend_hash_find>:
       │    zend_hash_find():
  0.84 │      push %r12
  0.04 │      push %rbp
  0.01 │      mov  %rsi,%rbp
  2.52 │      push %rbx
       │    zend_string_hash_val():
  8.01 │      mov  0x8(%rsi),%rax
       │    zend_hash_find():
  0.02 │      mov  %rdi,%rbx
       │    zend_string_hash_val():
  0.12 │      test %rax,%rax
  0.14 │    ↓ je   78
       │    zend_hash_find_bucket():
  5.63 │13:   or   0xc(%rbx),%eax
  0.28 │      mov  0x10(%rbx),%r12
  0.16 │      cltq
 25.03 │      mov  (%r12,%rax,4),%ebx
  1.98 │      cmp  $0xffffffff,%ebx
  0.56 │    ↓ je   a0
  0.85 │      shl  $0x5,%rbx
  0.50 │      add  %r12,%rbx
 15.20 │      cmp  0x18(%rbx),%rbp
 12.97 │    ↓ jne  68
       │    zend_hash_find():
  1.41 │32:   mov  %rbx,%rax
  0.60 │      pop  %rbx
  0.03 │      pop  %rbp
  1.25 │      pop  %r12
  1.83 │    ← ret
       │      nop
       │    zend_hash_find_bucket():
  0.26 │40:   mov  0x18(%rbx),%rdi
  0.04 │      test %rdi,%rdi
       │    ↓ je   53
       │    zend_string_equal_content():
  0.01 │      mov  0x10(%rbp),%rax
  0.01 │      cmp  %rax,0x10(%rdi)
  5.03 │    ↓ je   90
       │    zend_hash_find_bucket():
  1.06 │53:   mov  0xc(%rbx),%ebx
  0.11 │      cmp  $0xffffffff,%ebx
  0.15 │    ↓ je   a0
  0.33 │      shl  $0x5,%rbx
  0.24 │      add  %r12,%rbx
  1.90 │      cmp  0x18(%rbx),%rbp
  2.69 │    ↑ je   32
  2.00 │68:   mov  0x8(%rbp),%rax
  0.24 │      cmp  %rax,0x10(%rbx)

Is this a known performance issue within the PHP community? I'm seeking suggestions or insights on potential avenues for optimization. Your feedback and suggestions would be greatly appreciated.

PHP Version

master

Operating System

No response

Start by reading zend_hash_find_bucket and the related zend_hash_find and zend_hash_find_known_hash entry points, then reproduce the reported perf profile against the WordPress workload. Done requires a justified change with measurable improvement in that workload, while preserving hash lookup behavior.