This bugzilla service is closed. All entries have been migrated to
Bug 729 - EIGEN_ALLOCA is only defined on Linux and Windows with MSVC
Summary: EIGEN_ALLOCA is only defined on Linux and Windows with MSVC
Alias: None
Product: Eigen
Classification: Unclassified
Component: Core - general (show other bugs)
Version: 3.2
Hardware: All Other
: High Performance Problem
Assignee: Nobody
Depends on:
Blocks: 3.3
  Show dependency treegraph
Reported: 2014-01-21 14:27 UTC by Christoph Hertzberg
Modified: 2019-12-04 12:57 UTC (History)
2 users (show)


Description Christoph Hertzberg 2014-01-21 14:27:43 UTC
Checking the definition of EIGEN_ALLOCA in src/Core/util/Memory.h it appears that there is a default implementation only for Linux and Windows with MSVC. That excludes at least MacOS and Windows with MinGW/Cygwin (which all support alloca).
Comment 1 Gael Guennebaud 2014-01-21 17:19:06 UTC
Indeed, for safety reason we have been very conservative regarding the use of alloca. In particular, I'm not 100% sure alloca always work with MinGW/Cygwin. I remember we had an issue with mingw, but that was with the 3.4.5 version (!) which is not supported by Eigen anymore.
Comment 2 Christoph Hertzberg 2014-02-17 14:14:48 UTC
Could we produce a compile-time warning (or even an error?) if EIGEN_NO_MALLOC or EIGEN_RUNTIME_NO_MALLOC is defined, but EIGEN_ALLOCA is not?
Maybe with the hint that the user should provide a definition of EIGEN_ALLOCA if he wants to avoid heap allocations.

But we also should determine minimal versions of MacOS, MinGW and Cygwin which already provide alloca.
Comment 3 Christoph Hertzberg 2014-06-20 18:00:13 UTC
Would it be safe enough to add an 
  || (defined alloca)
to the #if condition?
Comment 4 Gael Guennebaud 2014-06-23 09:20:00 UTC
Adding "|| (defined alloca)" seems to be harmless, so go for it.
Comment 5 Christoph Hertzberg 2014-06-23 11:22:25 UTC
Fixed here:
Comment 6 Nobody 2019-12-04 12:57:08 UTC
-- GitLab Migration Automatic Message --

This bug has been migrated to's GitLab instance and has been closed from further activity.

You can subscribe and participate further through the new bug through this link to our GitLab instance:

Note You need to log in before you can comment on or make changes to this bug.