3229 Commits

Author SHA1 Message Date
Reid Kleckner
8f32e5f0d6 Rename llvm.frameescape and llvm.framerecover to localescape and localrecover
Summary:
Initially, these intrinsics seemed like part of a family of "frame"
related intrinsics, but now I think that's more confusing than helpful.
Initially, the LangRef specified that this would create a new kind of
allocation that would be allocated at a fixed offset from the frame
pointer (EBP/RBP). We ended up dropping that design, and leaving the
stack frame layout alone.

These intrinsics are really about sharing local stack allocations, not
frame pointers. I intend to go further and add an `llvm.localaddress()`
intrinsic that returns whatever register (EBP, ESI, ESP, RBX) is being
used to address locals, which should not be confused with the frame
pointer.

Naming suggestions at this point are welcome, I'm happy to re-run sed.

Reviewers: majnemer, nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11011

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241633 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-07 22:25:32 +00:00
Eric Christopher
ddf4c989ee Remove JumpInstrTableInfo.h as it is no longer used.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241517 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-06 22:55:20 +00:00
David Blaikie
b99e0eb947 Revert "[DWARF] Fix debug info generation for function static variables, typedefs, and records"
Caused PR24008

This reverts commit 37cb5f1c2db9f42d29f26b215585f56bb64ae4f5.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241176 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-01 18:07:16 +00:00
Benjamin Kramer
a2b83fd687 [AsmPrinter] Hide implementation details
NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241169 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-01 16:18:16 +00:00
Michael Kuperstein
37cb5f1c2d [DWARF] Fix debug info generation for function static variables, typedefs, and records
Function static variables, typedefs and records (class, struct or union) declared inside
a lexical scope were associated with the function as their parent scope, rather than the
lexical scope they are defined or declared in.

This fixes PR19238

Patch by: amjad.aboud@intel.com
Differential Revision: http://reviews.llvm.org/D9758

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241153 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-01 12:33:11 +00:00
Reid Kleckner
34c6bb0ef0 [SEH] Add new intrinsics for recovering and restoring parent frames
The incoming EBP value established by the runtime is actually a pointer
to the end of the EH registration object, and not the true parent
function frame pointer. Clang doesn't need llvm.x86.seh.exceptioninfo
anymore because we know that the exception info pointer is at a fixed
offset from this incoming EBP.

The llvm.x86.seh.recoverfp intrinsic takes an EBP value provided by the
EH runtime and returns a pointer that is usable with llvm.framerecover.

The llvm.x86.seh.restoreframe intrinsic is inserted by the 32-bit
specific preparation pass in blocks targetted by the EH runtime. It
re-establishes any physical registers used by the parent function to
address the stack, such as the frame, base, and stack pointers.

Neither of these intrinsics correctly handle stack realignment prologues
yet, but it's possible to add that later.

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D10848

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241125 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-30 22:46:59 +00:00
Adrian Prantl
85cd16c88e Debug info: Add dwarf backend support for DIModule.
rdar://problem/20965932

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241034 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-30 02:13:04 +00:00
Benjamin Kramer
17d7215661 [MMI] Use TinyPtrVector instead of PointerUnion with vector.
Also simplify duplicated code a bit. No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240990 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-29 20:21:55 +00:00
Adrian Prantl
1e7ecc8e57 Revert "Debug Info: One more bitfield bugfix. While yesterday's r240853 fixed"
This reverts commit 240890. Breaking the gdb buildbot.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240893 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-27 21:55:00 +00:00
Adrian Prantl
6b2ae13ea3 Debug Info: One more bitfield bugfix. While yesterday's r240853 fixed
the DW_AT_bit_offset computation, the byte offset is in fact also
endian-dependent as it needs to point to the storage unit containing the
most-significant bit of the the bitfield.
I'm so looking forward to emitting the endian-agnostic DWARF 3 version
instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240890 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-27 20:12:43 +00:00
Adrian Prantl
60bd365f59 Debug Info: Fix a bug in the DW_AT_bit_offset calculation that would
result in negative offsets and attempt a better job at documenting
the algorithm.

rdar://21082998

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240853 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-26 23:31:27 +00:00
Adrian Prantl
7cb828a34d Debug Info: Clarify the documentation for bitfields emission.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240835 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-26 21:27:30 +00:00
Duncan P. N. Exon Smith
2da1484e97 AsmPrinter: Use an intrusively linked list for DIE::Children
Replace the `std::vector<>` for `DIE::Children` with an intrusively
linked list.  This is a strict memory improvement: it requires no
auxiliary storage, and reduces `sizeof(DIE)` by one pointer.  It also
factors out the DIE-related malloc traffic.

This drops llc memory usage from 735 MB down to 718 MB, or ~2.3%.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;
see r236629 for details.)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240736 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-25 23:52:10 +00:00
Duncan P. N. Exon Smith
73e3fb6ba8 AsmPrinter: Convert DIE::Values to a linked list
Change `DIE::Values` to a singly linked list, where each node is
allocated on a `BumpPtrAllocator`.  In order to support `push_back()`,
the list is circular, and points at the tail element instead of the
head.  I abstracted the core list logic out to `IntrusiveBackList` so
that it can be reused for `DIE::Children`, which also cares about
`push_back()`.

This drops llc memory usage from 799 MB down to 735 MB, about 8%.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;
see r236629 for details.)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240733 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-25 23:46:41 +00:00
Bruno Cardoso Lopes
39b2e22f00 [AsmPrinter] Fix crash in handleIndirectSymViaGOTPCRel
Check for symbols in MCValue before using them. Bail out early in case
they are null. This fixes PR23779.

Differential Revision: http://reviews.llvm.org/D10712

rdar://problem/21532830

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240649 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-25 15:17:23 +00:00
Duncan P. N. Exon Smith
a0b5a74966 AsmPrinter: Cleanup DIEValue::EmitValue() API, NFC
Stop taking a `dwarf::Form` in `DIEValue::EmitValue()` and
`DIEValue::SizeOf()`, since they're always passed `DIEValue::getForm()`
anyway.  This is just left over from when `DIEValue` didn't know its own
form.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240566 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-24 18:48:11 +00:00
Rafael Espindola
9758b4ae95 Simplify the Mangler interface now that DataLayout is mandatory.
We only need to pass in a DataLayout when mangling a raw string, not when
constructing the mangler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240405 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-23 13:59:29 +00:00
Alexander Kornienko
cd52a7a381 Revert r240137 (Fixed/added namespace ending comments using clang-tidy. NFC)
Apparently, the style needs to be agreed upon first.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240390 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-23 09:49:53 +00:00
Duncan P. N. Exon Smith
f1c527b5c1 AsmPrinter: Don't emit empty .debug_loc entries
If we don't know how to represent a .debug_loc entry, skip the entry
entirely rather than emitting an empty one.  Similarly, if a .debug_loc
list has no entries, don't create the list.

We still want to create the variables, just in an optimized-out form
that doesn't have a DW_AT_location.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240244 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-21 16:54:56 +00:00
Duncan P. N. Exon Smith
01a8dc8ca6 AsmPrinter: Rewrite initialization of DbgVariable, NFC
There are three types of `DbgVariable`:
  - alloca variables, created based on the MMI table,
  - register variables, created based on DBG_VALUE instructions, and
  - optimized-out variables.

This commit reconfigures `DbgVariable` to make it easier to tell which
kind we have, and make initialization a little clearer.

For MMI/alloca variables, `FrameIndex.size()` must always equal
`Expr.size()`, and there shouldn't be an `MInsn`.  For register
variables (with a `MInsn`), `FrameIndex` must be empty, and `Expr`
should have 0 or 1 element depending on whether it has a complex
expression (registers with multiple locations use `DebugLocListIndex`).
Optimized-out variables shouldn't have any of these fields.

Moreover, this separates DBG_VALUE initialization until after the
variable is created, simplifying logic in a future commit that changes
`collectVariableInfo()` to stop creating empty .debug_loc entries/lists.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240243 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-21 16:50:43 +00:00
Alexander Kornienko
cf0db29df2 Fixed/added namespace ending comments using clang-tidy. NFC
The patch is generated using this command:

tools/clang/tools/extra/clang-tidy/tool/run-clang-tidy.py -fix \
  -checks=-*,llvm-namespace-comment -header-filter='llvm/.*|clang/.*' \
  llvm/lib/


Thanks to Eugene Kosov for the original patch!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240137 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-19 15:57:42 +00:00
David Majnemer
6d136d7300 [CodeGen] Don't emit a random reference to the personality function
This should fix issues we've been seeing with Darwin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240036 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-18 18:31:46 +00:00
Benjamin Kramer
24e04b80a5 [AsmPrinter] Make isRepeatedByteSequence smarter about odd integer types
- zext the value to alloc size first, then check if the value repeats
  with zero padding included. If so we can still emit a .space
- Do the checking with APInt.isSplat(8), which handles non-pow2 types
- Also handle large constants (bit width > 64)
- In a ConstantArray all elements have the same type, so it's sufficient
  to check the first constant recursively and then just compare if all
  following constants are the same by pointer compare

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239977 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-17 23:55:17 +00:00
David Majnemer
cc714e2142 Move the personality function from LandingPadInst to Function
The personality routine currently lives in the LandingPadInst.

This isn't desirable because:
- All LandingPadInsts in the same function must have the same
  personality routine.  This means that each LandingPadInst beyond the
  first has an operand which produces no additional information.

- There is ongoing work to introduce EH IR constructs other than
  LandingPadInst.  Moving the personality routine off of any one
  particular Instruction and onto the parent function seems a lot better
  than have N different places a personality function can sneak onto an
  exceptional function.

Differential Revision: http://reviews.llvm.org/D10429

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239940 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-17 20:52:32 +00:00
Rafael Espindola
3fea1651f6 Rename and improve emitSectionOffset.
Different object formats represent references from dwarf in different ways.

ELF uses a relocation to the referenced point (except for .dwo) and
COFF/MachO use the offset of the referenced point inside its section.

This patch renames emitSectionOffset because

* It doesn't produce an offset on ELF.
* It changes behavior depending on how DWARF is represented, so adding
dwarf to its name is probably a good thing.

The patch also adds an option to force the use of offsets.That avoids
funny looking code like

  if (!UseOffsets)
    Asm->emitSectionOffset....

It was correct, but read as if the ! was inverted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239866 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-16 23:22:02 +00:00
Daniel Sanders
7f5b833aa3 Replace string GNU Triples with llvm::Triple in TargetMachine::getTargetTriple(). NFC.
Summary:
This continues the patch series to eliminate StringRef forms of GNU triples
from the internals of LLVM that began in r239036.

Reviewers: rengolin

Reviewed By: rengolin

Subscribers: llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D10381


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239815 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-16 13:15:50 +00:00
Adrian Prantl
0f80e47db3 Debug Info IR: Switch DIObjCProperty to use DITypeRef.
This is a prerequisite for turning on ODR type uniquing for ObjC++.

rdar://problem/21377883

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239780 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-15 23:18:03 +00:00
NAKAMURA Takumi
145cdc632a AsmPrinter.cpp: Avoid crashes for targeting like "arm-mingw32". CurrentFnSym might not be <MCSymbolELF> here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239692 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-14 00:23:40 +00:00
NAKAMURA Takumi
82b72bed60 Reformat.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239691 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-14 00:23:33 +00:00
Reid Kleckner
2bd0221fa4 [WinEH] Put finally pointers in the handler scope table field
We were putting them in the filter field, which is correct for 64-bit
but wrong for 32-bit.

Also switch the order of scope table entry emission so outermost entries
are emitted first, and fix an obvious state assignment bug.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239574 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-11 23:37:18 +00:00
Reid Kleckner
3e16bd3aaf [WinEH] Create an llvm.x86.seh.exceptioninfo intrinsic
This intrinsic is like framerecover plus a load. It recovers the EH
registration stack allocation from the parent frame and loads the
exception information field out of it, giving back a pointer to an
EXCEPTION_POINTERS struct. It's designed for clang to use in SEH filter
expressions instead of accessing the EXCEPTION_POINTERS parameter that
is available on x64.

This required a minor change to MC to allow defining a label variable to
another absolute framerecover label variable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239567 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-11 22:32:23 +00:00
Rafael Espindola
6c56decee0 Generalize emitAbsoluteSymbolDiff.
This makes emitAbsoluteSymbolDiff always succeed and moves logic from the asm
printer to it.

The object one now also works on ELF. If two symbols are in the same fragment,
we will never move them apart.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239552 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-11 18:58:08 +00:00
Pete Cooper
5a118340dd Remove MachineModuleInfo::UsedFunctions as it has no users.
It hasn't been used since r130964.

This also removes MachineModuleInfo::isUsedFunction and
MachineModuleInfo::AnalyzeModule, both of which were only
there to support UsedFunctions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239501 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-11 01:04:56 +00:00
Reid Kleckner
3de99b70aa [WinEH] _except_handlerN uses 0 instead of 1 to indicate catch-all
Our usage of 1 was a holdover from __C_specific_handler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239482 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-10 18:14:07 +00:00
Reid Kleckner
6d7e69b227 Remove safeseh debug print and remove extra braces
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239449 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-10 01:13:44 +00:00
Reid Kleckner
c8e72e9126 [WinEH] Emit .safeseh directives for all 32-bit exception handlers
Use a "safeseh" string attribute to do this. You would think we chould
just accumulate the set of personalities like we do on dwarf, but this
fails to account for the LSDA-loading thunks we use for
__CxxFrameHandler3. Each of those needs to make it into .sxdata as well.
The string attribute seemed like the most straightforward approach.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239448 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-10 01:02:30 +00:00
Reid Kleckner
a8c0a9b042 Fix -Wsign-compare warning in WinException.cpp
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239445 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-10 00:04:53 +00:00
Reid Kleckner
bdcbc426af [WinEH] Add 32-bit SEH state table emission prototype
This gets all the handler info through to the asm printer and we can
look at the .xdata tables now. I've convinced one small catch-all test
case to work, but other than that, it would be a stretch to say this is
functional.

The state numbering algorithm avoids doing any scope reconstruction as
we do for C++ to simplify the implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239433 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-09 21:42:19 +00:00
David Blaikie
6eee2375d9 Revert "[DWARF] Fix a few corner cases in expression emission"
This reverts commit r239380 due to apparently GDB regressions:
http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/22562

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239420 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-09 18:01:51 +00:00
Keno Fischer
b4863a99c9 [DWARF] Fix a few corner cases in expression emission
Summary: I noticed an object file with `DW_OP_reg4 DW_OP_breg4 0` as a DWARF expression,
which I traced to a missing break (and `++I`) in this code snippet.
While I was at it, I also added support for a few other corner cases
along the same lines that I could think of.

Test Plan: Hand-crafted test case to exercises these cases is included.

Reviewers: echristo, dblaikie, aprantl

Reviewed By: aprantl

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10302

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239380 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-09 01:53:59 +00:00
Matt Arsenault
d99ce2f630 MC: Add target hook to control symbol quoting
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239370 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-09 00:31:39 +00:00
Rafael Espindola
f7e0685b9a Create a MCSymbolELF.
This create a MCSymbolELF class and moves SymbolSize since only ELF
needs a size expression.

This reduces the size of MCSymbol from 56 to 48 bytes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238801 91177308-0d34-0410-b5e6-96231b3b80d8
2015-06-02 00:25:12 +00:00
Jim Grosbach
586c0042da MC: Clean up MCExpr naming. NFC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238634 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-30 01:25:56 +00:00
Reid Kleckner
16e4a624c4 [WinEH] Emit EH tables for __CxxFrameHandler3 on 32-bit x86
Small (really small!) C++ exception handling examples work on 32-bit x86
now.

This change disables the use of .seh_* directives in WinException when
CFI is not in use. It also uses absolute symbol references in the tables
instead of imagerel32 relocations.

Also fixes a cache invalidation bug in MMI personality classification.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238575 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-29 17:00:57 +00:00
Reid Kleckner
178db50629 Rename Win64Exception.(cpp|h) to WinException.(cpp|h)
This is in preparation for reusing this for 32-bit x86 EH table
emission.  Also updates the type name for consistency. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238521 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-28 22:47:01 +00:00
Duncan P. N. Exon Smith
2c7cce70cd AsmPrinter: Stop exposing underlying DIE children list, NFC
Update `DIE` API to hide the implementation of `DIE::Children` so we can
swap it out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238468 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-28 19:56:34 +00:00
Duncan P. N. Exon Smith
bfecc6bdee AsmPrinter: Rename begin_values() => values_begin(), NFC
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238456 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-28 18:55:38 +00:00
Benjamin Kramer
331b719b2b [AsmPrinter] Destroy allocated DIEAbbrevs on teardown.
DIEAbbrev contains a SmallVector that can leak for overly large abbrevs. They
used to be owned by the DIE, but after the recent refactoring DWARFFile
allocates its own abbrevs.

Leak found by asan.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238418 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-28 12:55:43 +00:00
Duncan P. N. Exon Smith
2c46a37b03 AsmPrinter: Avoid a warning in NDEBUG, NFC
Should fix the -Werror release build:
http://lab.llvm.org:8011/builders/lld-x86_64-darwin13/builds/11113

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238375 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-27 23:02:36 +00:00
Duncan P. N. Exon Smith
59be554de4 AsmPrinter: Return added DIE from DIE::addChild()
Change `DIE::addChild()` to return a reference to the just-added node,
and update consumers to use it directly.  An upcoming commit will
abstract away (and eventually change) the underlying storage of
`DIE::Children`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238372 91177308-0d34-0410-b5e6-96231b3b80d8
2015-05-27 22:59:03 +00:00