Identified with misc-include-cleaner.

SectionMemoryManager's default memory mapper used to be a global static
object. If the SectionMemoryManager itself is a global static
object, it might be destroyed after its memory mapper and thus couldn't
use it from the destructor.

The Kaleidoscope tutorial reproduced this situation with MSVC for a long time.
Since 47f5c54f997a59bb2c65 it's triggered with GCC as well. The solution from
this patch was proposed in the existing review https://reviews.llvm.org/D107087
before, but it didn't move forward.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D154338

Identified with modernize-use-nullptr.

This reverts commit 63838d88145feaeb839efff8f40ab1e98597e423, which broke tests
on some bots. See e.g. https://lab.llvm.org/buildbot#builders/109/builds/22561

This commit fixes an order-of-initialization issue: If the default mmapper
object is destroyed while some global SectionMemoryManager is still using it
then calls to the mapper from ~SectionMemoryManager will fail. This issue was
causing failures when running the LLVM Kaleidoscope examples on windows.

Switching to a ManagedStatic solves the initialization order issue.

Patch by Justice Adams. Thanks Justice!

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D107087

The code in SectionMemoryManager.cpp unnecessarily maps
read-only data sections with the READ+EXECUTE flags. This is
undesirable from a security stand-point.

Moreover, on the Fuchsia platform, which is now very strict
about mapping pages with the EXECUTE permission, this simply
fails, because the section's pages were initially allocated
with only the READ+WRITE flags.

A more detailed description of the issue can be found in this
public SwiftShader bug:

  https://issuetracker.google.com/issues/154586551

This patch just restrict the mapping to the READ flag for ROData
sections. Code sections are still mapped with READ+EXECUTE as
expected.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D78574

When allocating a new memory block in SectionMemoryManager, initialize
the Near hint for the other memory groups if they have not been set
already.

Patch by Dana Koch. Thanks Dana!

Rename member 'Size' to 'AllocatedSize' in order to provide a hint that the
allocated size may be different than the requested size. Comments are added to
clarify this point.  Updated the InMemoryBuffer in FileOutputBuffer.cpp to track
the requested buffer size.

Patch by Machiel van Hooren. Thanks Machiel!

https://reviews.llvm.org/D61599

llvm-svn: 361195