Commit Graph

925 Commits

Author SHA1 Message Date
Duncan P. N. Exon Smith
7bf73bd378 IPO: Add use-list-order verifier
Add a -verify-use-list-order pass, which shuffles use-list order, writes
to bitcode, reads back, and verifies that the (shuffled) order matches.

  - The utility functions live in lib/IR/UseListOrder.cpp.

  - Moved (and renamed) the command-line option to enable writing
    use-lists, so that this pass can return early if the use-list orders
    aren't being serialized.

It's not clear that this pass is the right direction long-term (perhaps
a separate tool instead?), but short-term it's a great way to test the
use-list order prototype.  I've added an XFAIL-ed testcase that I'm
hoping to get working pretty quickly.

This is part of PR5680.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213945 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-25 14:49:26 +00:00
Gerolf Hoflehner
d94715e273 MergedLoadStoreMotion pass
Merges equivalent loads on both sides of a hammock/diamond
and hoists into into the header.
Merges equivalent stores on both sides of a hammock/diamond
and sinks it to the footer.
Can enable if conversion and tolerate better load misses
and store operand latencies.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213396 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-18 19:13:09 +00:00
Peter Collingbourne
ca3c5b8722 Give SplitBlockAndInsertIfThen the ability to update a domtree.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213045 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-15 04:40:27 +00:00
Hal Finkel
73118c4128 Feeding isSafeToSpeculativelyExecute its DataLayout pointer
isSafeToSpeculativelyExecute can optionally take a DataLayout pointer. In the
past, this was mainly used to make better decisions regarding divisions known
not to trap, and so was not all that important for users concerned with "cheap"
instructions. However, now it also helps look through bitcasts for
dereferencable loads, and will also be important if/when we add a
dereferencable pointer attribute.

This is some initial work to feed a DataLayout pointer through to callers of
isSafeToSpeculativelyExecute, generally where one was already available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212720 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-10 14:41:31 +00:00
Alexey Samsonov
3e51f754ad Decouple llvm::SpecialCaseList text representation and its LLVM IR semantics.
Turn llvm::SpecialCaseList into a simple class that parses text files in
a specified format and knows nothing about LLVM IR. Move this class into
LLVMSupport library. Implement two users of this class:
  * DFSanABIList in DFSan instrumentation pass.
  * SanitizerBlacklist in Clang CodeGen library.
The latter will be modified to use actual source-level information from frontend
(source file names) instead of unstable LLVM IR things (LLVM Module identifier).

Remove dependency edge from ClangCodeGen/ClangDriver to LLVMTransformUtils.

No functionality change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212643 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-09 19:40:08 +00:00
Alexey Samsonov
f78f9fda31 [ASan] Completely remove sanitizer blacklist file from instrumentation pass.
All blacklisting logic is now moved to the frontend (Clang).
If a function (or source file it is in) is blacklisted, it doesn't
get sanitize_address attribute and is therefore not instrumented.
If a global variable (or source file it is in) is blacklisted, it is
reported to be blacklisted by the entry in llvm.asan.globals metadata,
and is not modified by the instrumentation.

The latter may lead to certain false positives - not all the globals
created by Clang are described in llvm.asan.globals metadata (e.g,
RTTI descriptors are not), so we may start reporting errors on them
even if "module" they appear in is blacklisted. We assume it's fine
to take such risk:
  1) errors on these globals are rare and usually indicate wild memory access
  2) we can lazily add descriptors for these globals into llvm.asan.globals
     lazily.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212505 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-08 00:50:49 +00:00
Alexey Samsonov
6140939365 Remove top-level Clang -fsanitize= flags for optional ASan features.
Init-order and use-after-return modes can currently be enabled
by runtime flags. use-after-scope mode is not really working at the
moment.

The only problem I see is that users won't be able to disable extra
instrumentation for init-order and use-after-scope by a top-level Clang flag.
But this instrumentation was implicitly enabled for quite a while and
we didn't hear from users hurt by it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210924 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-13 17:53:44 +00:00
Alexey Samsonov
f50e395308 Remove sanitizer blacklist from ASan/TSan/MSan function passes.
Instrumentation passes now use attributes
address_safety/thread_safety/memory_safety which are added by Clang frontend.
Clang parses the blacklist file and adds the attributes accordingly.

Currently blacklist is still used in ASan module pass to disable instrumentation
for certain global variables. We should fix this as well by collecting the
set of globals we're going to instrument in Clang and passing it to ASan
in metadata (as we already do for dynamically-initialized globals and init-order
checking).

This change also removes -tsan-blacklist and -msan-blacklist LLVM commandline
flags in favor of -fsanitize-blacklist= Clang flag.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210038 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-02 18:08:27 +00:00
Karthik Bhat
8ffc96a163 Allow vectorization of intrinsics such as powi,cttz and ctlz in Loop and SLP Vectorizer.
This patch adds support to vectorize intrinsics such as powi, cttz and ctlz in Vectorizer. These intrinsics are different from other
intrinsics as second argument to these function must be same in order to vectorize them and it should be represented as a scalar.
Review: http://reviews.llvm.org/D3851#inline-32769 and http://reviews.llvm.org/D3937#inline-32857


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209873 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-30 04:31:24 +00:00
Michael J. Spencer
ed0e90576d [LoadCombine] Missed a file.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209792 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-29 02:05:37 +00:00
Michael J. Spencer
8bfb46e790 Add LoadCombine pass.
This pass is disabled by default. Use -combine-loads to enable in -O[1-3]

Differential revision: http://reviews.llvm.org/D3580

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209791 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-29 01:55:07 +00:00
Owen Anderson
866ed7f63f Make the LoopRotate pass's maximum header size configurable both programmatically
and via the command line, mirroring similar functionality in LoopUnroll.  In
situations where clients used custom unrolling thresholds, their intent could
previously be foiled by LoopRotate having a hardcoded threshold.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209617 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-26 08:58:51 +00:00
NAKAMURA Takumi
a1b1165f30 Reformat linefeeds.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209609 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-26 00:25:26 +00:00
NAKAMURA Takumi
a9b0742276 Trailing whitespace.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209608 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-26 00:25:09 +00:00
Peter Collingbourne
62692b442a Add an extension point for peephole optimizers.
This extension point allows adding passes that perform peephole optimizations
similar to the instruction combiner. These passes will be inserted after
each instance of the instruction combiner pass.

Differential Revision: http://reviews.llvm.org/D3905

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209595 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-25 10:27:02 +00:00
Benjamin Kramer
29e068bac0 Flip on vectorization of bswap intrinsics.
The cost model conservatively assumes that it will always get scalarized and
that's about as good as we can get with the generic TTI; reasoning whether a
shuffle with an efficient lowering is available is hard. We can override that
conservative estimate for some targets in the future.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209125 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-19 13:48:08 +00:00
NAKAMURA Takumi
6f1b92a0d4 Reformat blank lines.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209106 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-19 04:43:26 +00:00
NAKAMURA Takumi
14c7036563 Whitespace.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209105 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-19 04:43:03 +00:00
Richard Smith
c51c340989 [modules] Add missing #include.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208276 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-08 02:34:32 +00:00
Richard Smith
36ecb2ee9d Re-commit r208025, reverted in r208030, with a fix for a conformance issue
which GCC detects and Clang does not!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208033 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-06 01:44:26 +00:00
Richard Smith
f3a199b2ae Revert r208025, which made buildbots unhappy for unknown reasons.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208030 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-06 01:26:00 +00:00
Richard Smith
245e8bdfba Add llvm::function_ref (and a couple of uses of it), representing a type-erased reference to a callable object.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208025 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-06 01:01:29 +00:00
Karthik Bhat
486ad6262e Vectorize intrinsic math function calls in SLPVectorizer.
This patch adds support to recognize and vectorize intrinsic math functions in SLPVectorizer.
Review: http://reviews.llvm.org/D3560 and http://reviews.llvm.org/D3559


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207901 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-03 09:59:54 +00:00
Nico Weber
3a5b1043d0 Teach GlobalDCE how to remove empty global_ctor entries.
This moves most of GlobalOpt's constructor optimization
code out of GlobalOpt into Transforms/Utils/CDtorUtils.{h,cpp}. The
public interface is a single function OptimizeGlobalCtorsList() that
takes a predicate returning which constructors to remove.

GlobalOpt calls this with a function that statically evaluates all
constructors, just like it did before. This part of the change is
behavior-preserving.

Also add a call to this from GlobalDCE with a filter that removes global
constructors that contain a "ret" instruction and nothing else – this
fixes PR19590.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207856 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-02 18:35:25 +00:00
Eli Bendersky
167a57ca45 Add an optimization that does CSE in a group of similar GEPs.
This optimization merges the common part of a group of GEPs, so we can compute
each pointer address by adding a simple offset to the common part.

The optimization is currently only enabled for the NVPTX backend, where it has
a large payoff on some benchmarks.

Review: http://reviews.llvm.org/D3462

Patch by Jingyue Wu.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207783 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-01 18:38:36 +00:00
Craig Topper
8d7221ccf5 [C++] Use 'nullptr'. Transforms edition.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207196 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-25 05:29:35 +00:00
Karthik Bhat
ac16f0e024 Allow vectorization of bit intrinsics in BB Vectorizer.
This patch adds support for vectorization of  bit intrinsics such as bswap,ctpop,ctlz,cttz.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207174 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-25 03:33:48 +00:00
Chandler Carruth
283b399377 [Modules] Make Support/Debug.h modular. This requires it to not change
behavior based on other files defining DEBUG_TYPE, which means it cannot
define DEBUG_TYPE at all. This is actually better IMO as it forces folks
to define relevant DEBUG_TYPEs for their files. However, it requires all
files that currently use DEBUG(...) to define a DEBUG_TYPE if they don't
already. I've updated all such files in LLVM and will do the same for
other upstream projects.

This still leaves one important change in how LLVM uses the DEBUG_TYPE
macro going forward: we need to only define the macro *after* header
files have been #include-ed. Previously, this wasn't possible because
Debug.h required the macro to be pre-defined. This commit removes that.
By defining DEBUG_TYPE after the includes two things are fixed:

- Header files that need to provide a DEBUG_TYPE for some inline code
  can do so by defining the macro before their inline code and undef-ing
  it afterward so the macro does not escape.

- We no longer have rampant ODR violations due to including headers with
  different DEBUG_TYPE definitions. This may be mostly an academic
  violation today, but with modules these types of violations are easy
  to check for and potentially very relevant.

Where necessary to suppor headers with DEBUG_TYPE, I have moved the
definitions below the includes in this commit. I plan to move the rest
of the DEBUG_TYPE macros in LLVM in subsequent commits; this one is big
enough.

The comments in Debug.h, which were hilariously out of date already,
have been updated to reflect the recommended practice going forward.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206822 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-21 22:55:11 +00:00
Richard Smith
f4a2635c25 Add missing #include found by modules build.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206726 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-20 23:39:19 +00:00
Duncan P. N. Exon Smith
bf1d0f417e PMBuilder: Expose an option to disable tail calls
Adds API to allow frontends to disable tail calls in PassManagerBuilder.

<rdar://problem/16050591>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206542 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-18 01:05:15 +00:00
Craig Topper
0b6cb7104b [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206252 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-15 06:32:26 +00:00
Craig Topper
4ba844388c [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206142 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-14 00:51:57 +00:00
Arnold Schwaighofer
b0ee2374ce SLPVectorizer: Only vectorize intrinsics whose operands are widened equally
The vectorizer only knows how to vectorize intrinics by widening all operands by
the same factor.

Patch by Tyler Nowicki!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205855 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-09 14:20:47 +00:00
Duncan P. N. Exon Smith
3845c071a7 Revert "Reapply "LTO: add API to set strategy for -internalize""
This reverts commit r199244.

Conflicts:
	include/llvm-c/lto.h
	include/llvm/LTO/LTOCodeGenerator.h
	lib/LTO/LTOCodeGenerator.cpp

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205471 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-02 22:05:57 +00:00
Hal Finkel
6bbb01bbf8 Move partial/runtime unrolling late in the pipeline
The generic (concatenation) loop unroller is currently placed early in the
standard optimization pipeline. This is a good place to perform full unrolling,
but not the right place to perform partial/runtime unrolling. However, most
targets don't enable partial/runtime unrolling, so this never mattered.

However, even some x86 cores benefit from partial/runtime unrolling of very
small loops, and follow-up commits will enable this. First, we need to move
partial/runtime unrolling late in the optimization pipeline (importantly, this
is after SLP and loop vectorization, as vectorization can drastically change
the size of a loop), while keeping the full unrolling where it is now. This
change does just that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205264 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-31 23:23:51 +00:00
Mark Seaborn
9bb9615e1f Remove LowerInvoke's obsolete "-enable-correct-eh-support" option
This option caused LowerInvoke to generate code using SJLJ-based
exception handling, but there is no code left that interprets the
jmp_buf stack that the resulting code maintained (llvm.sjljeh.jblist).
This option has been obsolete for a while, and replaced by
SjLjEHPrepare.

This leaves the default behaviour of LowerInvoke, which is to convert
invokes to calls.

Differential Revision: http://llvm-reviews.chandlerc.com/D3136

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204388 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-20 19:54:47 +00:00
Evgeniy Stepanov
610469f4c2 [msan] Origin tracking with history.
LLVM part of MSan implementation of advanced origin tracking,
when we record not only creation point, but all locations where
an uninitialized value was stored to memory, too.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204151 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-18 13:30:56 +00:00
NAKAMURA Takumi
7f0871c97f Untabify.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204020 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-16 23:58:43 +00:00
Eli Bendersky
ce306f9f99 Move duplicated code into a helper function (exposed through overload).
There's a bit of duplicated "magic" code in opt.cpp and Clang's CodeGen that
computes the inliner threshold from opt level and size opt level.

This patch moves the code to a function that lives alongside the inliner itself,
providing a convenient overload to the inliner creation.

A separate patch can be committed to Clang to use this once it's committed to
LLVM. Standalone tools that use the inlining pass can also avoid duplicating
this code and fearing it will go out of sync.

Note: this patch also restructures the conditinal logic of the computation to
be cleaner.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203669 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-12 16:12:36 +00:00
Alon Mishne
e74c0bf111 Cloning a function now also clones its debug metadata if 'ModuleLevelChanges' is true.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203662 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-12 14:42:51 +00:00
Craig Topper
7b62be28cb [C++11] Add 'override' keyword to virtual methods that override their base class.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202953 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-05 09:10:37 +00:00
Chandler Carruth
03e36d752c [Modules] Move CFG.h to the IR library as it defines graph traits over
IR types.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202827 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-04 11:45:46 +00:00
Chandler Carruth
7225e27b4c [Modules] Move ValueMap to the IR library. While this class does not
directly care about the Value class (it is templated so that the key can
be any arbitrary Value subclass), it is in fact concretely tied to the
Value class through the ValueHandle's CallbackVH interface which relies
on the key type being some Value subclass to establish the value handle
chain.

Ironically, the unittest is already in the right library.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202824 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-04 11:26:31 +00:00
Chandler Carruth
eb3d76da81 [Modules] Move ValueHandle into the IR library where Value itself lives.
Move the test for this class into the IR unittests as well.

This uncovers that ValueMap too is in the IR library. Ironically, the
unittest for ValueMap is useless in the Support library (honestly, so
was the ValueHandle test) and so it already lives in the IR unittests.
Mmmm, tasty layering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202821 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-04 11:17:44 +00:00
Chandler Carruth
bd7cba0d81 [Modules] Move GetElementPtrTypeIterator into the IR library. As its
name might indicate, it is an iterator over the types in an instruction
in the IR.... You see where this is going.

Another step of modularizing the support library.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202815 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-04 10:40:04 +00:00
Diego Novillo
f05b45fdb2 Pass to emit DWARF path discriminators.
DWARF discriminators are used to distinguish multiple control flow paths
on the same source location. When this happens, instructions across
basic block boundaries will share the same debug location.

This pass detects this situation and creates a new lexical scope to one
of the two instructions. This lexical scope is a child scope of the
original and contains a new discriminator value. This discriminator is
then picked up from MCObjectStreamer::EmitDwarfLocDirective to be
written on the object file.

This fixes http://llvm.org/bugs/show_bug.cgi?id=18270.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202752 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-03 20:06:11 +00:00
Quentin Colombet
8048c44580 [CodeGenPrepare] Move CodeGenPrepare into lib/CodeGen.
CodeGenPrepare uses extensively TargetLowering which is part of libLLVMCodeGen.
This is a layer violation which would introduce eventually a dependence on
CodeGen in ScalarOpts.

Move CodeGenPrepare into libLLVMCodeGen to avoid that.

Follow-up of <rdar://problem/15519855>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201912 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-22 00:07:45 +00:00
Rafael Espindola
39d8dcb53b Rename some member variables from TD to DL.
TargetData was renamed DataLayout back in r165242.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201581 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-18 15:33:12 +00:00
Stephen Hines
d60c43b4f3 Don't build DFSan functionality for Android.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201362 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-13 21:21:09 +00:00
Chandler Carruth
5ea4a54551 [LPM] Fix PR18616 where the shifts to the loop pass manager to extract
LCSSA from it caused a crasher with the LoopUnroll pass.

This crasher is really nasty. We destroy LCSSA form in a suprising way.
When unrolling a loop into an outer loop, we not only need to restore
LCSSA form for the outer loop, but for all children of the outer loop.
This is somewhat obvious in retrospect, but hey!

While this seems pretty heavy-handed, it's not that bad. Fundamentally,
we only do this when we unroll a loop, which is already a heavyweight
operation. We're unrolling all of these hypothetical inner loops as
well, so their size and complexity is already on the critical path. This
is just adding another pass over them to re-canonicalize.

I have a test case from PR18616 that is great for reproducing this, but
pretty useless to check in as it relies on many 10s of nested empty
loops that get unrolled and deleted in just the right order. =/ What's
worse is that investigating this has exposed another source of failure
that is likely to be even harder to test. I'll try to come up with test
cases for these fixes, but I want to get the fixes into the tree first
as they're causing crashes in the wild.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200273 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-28 01:25:38 +00:00