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Add IAS/EHABI changes to release notes

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204134 91177308-0d34-0410-b5e6-96231b3b80d8
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Renato Golin 2014-03-18 10:16:15 +00:00
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@ -37,9 +37,6 @@ Non-comprehensive list of changes in this release
* All backends have been changed to use the MC asm printer and support for the
non MC one has been removed.
* The ARM back-end now has the EHABI exception handling enabled by default. Use
`-arm-disable-ehabi` to turn it off (both landing pads and unwind tables).
* Clang can now successfully self-host itself on Linux/Sparc64 and on
FreeBSD/Sparc64.
@ -74,6 +71,38 @@ Non-comprehensive list of changes in this release
Makes programs 10x faster by doing Special New Thing.
Changes to the ARM Backend
--------------------------
Since release 3.3, a lot of new features have been included in the ARM
back-end but weren't production ready (ie. well tested) on release 3.4.
Just after the 3.4 release, we started heavily testing two major parts
of the back-end: the integrated assembler (IAS) and the ARM exception
handling (EHABI), and now they are enabled by default on LLVM/Clang.
The IAS received a lot of GNU extensions and directives, as well as some
specific pre-UAL instructions. Not all remaining directives will be
implemented, as we made judgement calls on the need versus the complexity,
and have chosen simplicity and future compatibility where hard decisions
had to be made. The major difference is, as stated above, the IAS validates
all inline ASM, not just for object emission, and that cause trouble with
some uses of inline ASM as pre-processor magic.
So, while the IAS is good enough to compile large projects (including most
of the Linux kernel), there are a few things that we can't (and probably
won't) do. For those cases, please use ``-fno-integrated-as`` in Clang.
Exception handling is another big change. After extensive testing and
changes to cooperate with Dwarf unwinding, EHABI is enabled by default.
The options ``-arm-enable-ehabi`` and ``-arm-enable-ehabi-descriptors``,
which were used to enable EHABI in the previous releases, are removed now.
This means all ARM code will emit EH unwind tables, or CFI unwinding (for
debug/profiling), or both. To avoid run-time inconsistencies, C code will
also emit EH tables (in case they interoperate with C++ code), as is the
case for other architectures (ex. x86_64). You can disable them via the
flag ``-fno-unwind-tables`` in Clang.
External Open Source Projects Using LLVM 3.5
============================================