[arrow] branch master updated: MINOR: [C++] Move static declaration to non-static declaration to improve performance (#13222)

[yibocai]

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The following commit(s) were added to refs/heads/master by this push:
     new 56cdaae781 MINOR: [C++] Move static declaration to non-static 
declaration to improve performance (#13222)
56cdaae781 is described below

commit 56cdaae781ba792df8b085ff4022796344b06e3b
Author: Weston Pace <weston.p...@gmail.com>
AuthorDate: Mon May 30 15:25:42 2022 -1000

    MINOR: [C++] Move static declaration to non-static declaration to improve 
performance (#13222)
    
    According to conbench there was a slight regression on #12957 .  Poking 
around a bit it seems that a static local variable is implemented using some 
kind of global lock (__cxa_guard_acquire / __cxa_guard_release).  On the other 
hand, constructing an empty shared_ptr is cheap (two pointers are set to 0).  
So if we care about performance here we probably don't want `static`.  This may 
be what is causing the conbench issue.
    
    Lead-authored-by: Weston Pace <weston.p...@gmail.com>
    Co-authored-by: Antoine Pitrou <anto...@python.org>
    Signed-off-by: Yibo Cai <yibo....@arm.com>
---
 cpp/src/arrow/compute/exec/expression.cc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/cpp/src/arrow/compute/exec/expression.cc 
b/cpp/src/arrow/compute/exec/expression.cc
index e23bd0683a..a65379460d 100644
--- a/cpp/src/arrow/compute/exec/expression.cc
+++ b/cpp/src/arrow/compute/exec/expression.cc
@@ -107,9 +107,12 @@ ValueDescr Expression::descr() const {
   return CallNotNull(*this)->descr;
 }
 
+// This is a module-global singleton to avoid synchronization costs of a
+// function-static singleton.
+static const std::shared_ptr<DataType> kNoType;
+
 const std::shared_ptr<DataType>& Expression::type() const {
-  static const std::shared_ptr<DataType> no_type;
-  if (impl_ == nullptr) return no_type;
+  if (impl_ == nullptr) return kNoType;
 
   if (auto lit = literal()) {
     return lit->type();