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          Avoid unnecessary arena allocations in expand_pattern().
          #65463
        
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    Avoid unnecessary arena allocations in expand_pattern().
  
  #65463
              
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nnethercote:rm-arena-allocation-from-expand_pattern
  
      
      
   
  Oct 20, 2019 
              
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    `expand_pattern()` has two callsites. One of them needs arena allocation, but the other does not. This commit moves the arena allocation out of the function. This avoids the allocation of many 4 KiB page arena chunks that only hold a single small allocation. It reduces the number of bytes allocated by up to 2% for various benchmarks, albeit without only a very small improvement in runtime.
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| r? @varkor | 
| Let's block this on landing #65160? | 
| 📌 Commit c4deea2 has been approved by  | 
    
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…m-expand_pattern, r=varkor Avoid unnecessary arena allocations in `expand_pattern()`. `expand_pattern()` has two callsites. One of them needs arena allocation, but the other does not. This commit moves the arena allocation out of the function. This avoids the allocation of many 4 KiB page arena chunks that only hold a single small allocation. It reduces the number of bytes allocated by up to 2% for various benchmarks, albeit without only a very small improvement in runtime.
    
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…m-expand_pattern, r=varkor Avoid unnecessary arena allocations in `expand_pattern()`. `expand_pattern()` has two callsites. One of them needs arena allocation, but the other does not. This commit moves the arena allocation out of the function. This avoids the allocation of many 4 KiB page arena chunks that only hold a single small allocation. It reduces the number of bytes allocated by up to 2% for various benchmarks, albeit without only a very small improvement in runtime.
    
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Rollup of 5 pull requests Successful merges: - #65460 (Clean up `contains()` `insert()` chains on HashSet) - #65463 (Avoid unnecessary arena allocations in `expand_pattern()`.) - #65579 (Changed `resolve_type_vars_with_obligations` to also resolve const inference variables) - #65605 (Remove unreachable unit tuple compare binop codegen) - #65626 (trivial typo fix) Failed merges: r? @ghost
  
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expand_pattern()has two callsites. One of them needs arenaallocation, but the other does not.
This commit moves the arena allocation out of the function. This avoids
the allocation of many 4 KiB page arena chunks that only hold a single
small allocation. It reduces the number of bytes allocated by up to 2%
for various benchmarks, albeit without only a very small improvement in
runtime.