On MSVC, std::deque degenerates to a list of pointers, which defeats

its purpose of reducing allocator load and memory fragmentation.
microsoft/STL#147 (comment)
Slic3r::deque<> compiles to boost::container::deque<> on Windows,
to std::deque<> on other systems.
SeamPlacer newly uses Slic3r::deque<>.

src/libslic3r/GCode/SeamPlacer.hpp

@@ -6,6 +6,7 @@
 #include <memory>
 #include <atomic>
 
+#include "libslic3r/libslic3r.h"
 #include "libslic3r/ExtrusionEntity.hpp"
 #include "libslic3r/Polygon.hpp"
 #include "libslic3r/PrintConfig.hpp"
@@ -93,7 +94,7 @@ struct PrintObjectSeamData
 
     struct LayerSeams
     {
-        std::deque<SeamPlacerImpl::Perimeter>       perimeters;
+        Slic3r::deque<SeamPlacerImpl::Perimeter>    perimeters;
         std::vector<SeamPlacerImpl::SeamCandidate>  points;
         std::unique_ptr<SeamCandidatesTree>         points_tree;
     };

src/libslic3r/libslic3r.h

@@ -23,6 +23,13 @@
 #include <cmath>
 #include <type_traits>
 
+#ifdef _WIN32
+// On MSVC, std::deque degenerates to a list of pointers, which defeats its purpose of reducing allocator load and memory fragmentation.
+// https://github.com/microsoft/STL/issues/147#issuecomment-1090148740
+// Thus it is recommended to use boost::container::deque instead.
+#include <boost/container/deque.hpp>
+#endif // _WIN32
+
 #include "Technologies.hpp"
 #include "Semver.hpp"
 
@@ -73,6 +80,16 @@ namespace Slic3r {
 
 extern Semver SEMVER;
 
+// On MSVC, std::deque degenerates to a list of pointers, which defeats its purpose of reducing allocator load and memory fragmentation.
+template<class T, class Allocator = std::allocator<T>>
+using deque = 
+#ifdef _WIN32
+    // Use boost implementation, which allocates blocks of 512 bytes instead of blocks of 8 bytes.
+    boost::container::deque<T, Allocator>;
+#else // _WIN32
+    std::deque<T, Allocator>;
+#endif // _WIN32
+
 template<typename T, typename Q>
 inline T unscale(Q v) { return T(v) * T(SCALING_FACTOR); }
 

src/libslic3r/pchheader.hpp

@@ -64,6 +64,12 @@
 #include <boost/config.hpp>
 #include <boost/config/warning_disable.hpp>
 #include <boost/container/small_vector.hpp>
+#ifdef _WIN32
+// On MSVC, std::deque degenerates to a list of pointers, which defeats its purpose of reducing allocator load and memory fragmentation.
+// https://github.com/microsoft/STL/issues/147#issuecomment-1090148740
+// Thus it is recommended to use boost::container::deque instead.
+#include <boost/container/deque.hpp>
+#endif // _WIN32
 #include <boost/date_time/local_time/local_time.hpp>
 #include <boost/date_time/posix_time/posix_time.hpp>
 #include <boost/filesystem.hpp>