12102 Commits

Author SHA1 Message Date
Timur Iskhodzhanov
6a490ac188 Fix a typo
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222426 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-20 11:48:58 +00:00
NAKAMURA Takumi
f9f464d44b SimplifyCFG.cpp: Tweak to let msc17 compliant.
- Use LLVM_DELETED_FUNCTION.
  - Don't use member initializers.
  - Don't use initializer list.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222422 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-20 08:59:02 +00:00
Mehdi Amini
b3e705ed1d SimplifyCFG: Refactor GatherConstantCompares() result in a struct
Code seems cleaner and easier to understand this way




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222416 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-20 06:51:02 +00:00
Chad Rosier
503ec9826c Revert "[Reassociate] As the expression tree is rewritten make sure the operands are"
This reverts commit r222142.  This is causing/exposing an execution-time regression
in spec2006/gcc and coremark on AArch64/A57/Ofast.

Conflicts:

	test/Transforms/Reassociate/optional-flags.ll

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222398 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 23:21:20 +00:00
Nico Weber
660bac6a57 Try to fix MSVS build after r222384. No intended behavior change.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222386 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 21:16:11 +00:00
Mehdi Amini
30bd0c753e SimplifyCFG: turn recursive GatherConstantCompares into iterative
A long sequence of || or && could lead to a stack explosion.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222384 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 20:09:11 +00:00
Suyog Sarda
ca72befdb5 Vectorize a reduction chain feeding into a 'return' statement.
e.x 
return (a[0]+b[0]) + (a[1]+b[1])

Differential Revision: http://reviews.llvm.org/D6227



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222364 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 16:07:38 +00:00
Arnaud A. de Grandmaison
beeec3231e Fix tail recursion elimination
When the BasicBlock containing the return instrution has a PHI with 2
incoming values, FoldReturnIntoUncondBranch will remove the no longer
used incoming value and remove the no longer needed phi as well. This
leaves us with a BB that no longer has a PHI, but the subsequent call
to FoldReturnIntoUncondBranch from FoldReturnAndProcessPred will not
remove the return instruction (which still uses the result of the call
instruction). This prevents EliminateRecursiveTailCall to remove
the value, as it is still being used in a basicblock which has no
predecessors.

The basicblock can not be erased on the spot, because its iterator is
still being used in runTRE.

This issue was exposed when removing the threshold on size for lifetime
marker insertion for named temporaries in clang. The testcase is a much
reduced version of peelOffOuterExpr(const Expr*, const ExplodedNode *)
from clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222354 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 13:32:51 +00:00
David Blaikie
5401ba7099 Update SetVector to rely on the underlying set's insert to return a pair<iterator, bool>
This is to be consistent with StringSet and ultimately with the standard
library's associative container insert function.

This lead to updating SmallSet::insert to return pair<iterator, bool>,
and then to update SmallPtrSet::insert to return pair<iterator, bool>,
and then to update all the existing users of those functions...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222334 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 07:49:26 +00:00
Hao Liu
eb52f383c2 [SeparateConstOffsetFromGEP] Allow SeparateConstOffsetFromGEP pass to lower GEPs.
If LowerGEP is enabled, it can lower a GEP with multiple indices into GEPs with a single index
or arithmetic operations. Lowering GEPs can always extract structure indices. Lowering GEPs can
also give use more optimization opportunities. It can benefit passes like CSE, LICM and CGP.

Reviewed in http://reviews.llvm.org/D5864


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222328 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 06:24:44 +00:00
Kostya Serebryany
0dd5e22d89 [asan] add experimental basic-block tracing to asan-coverage; also fix -fsanitize-coverage=3 which was broken by r221718
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222290 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 00:22:58 +00:00
Kostya Serebryany
f82e60f03d Introduce llvm::SplitAllCriticalEdges
Summary:
move the code from BreakCriticalEdges::runOnFunction()
into a separate utility function llvm::SplitAllCriticalEdges()
so that it can be used independently.
No functionality change intended.

Test Plan: check-llvm

Reviewers: nlewycky

Reviewed By: nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D6313

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222288 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 00:17:31 +00:00
Manman Ren
2b82868de5 Revert r222039 because of bot failure.
http://lab.llvm.org:8080/green/job/clang-Rlto_master/298/
Hopefully, bot will be green. If not, we will re-submit the commit.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222287 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-19 00:13:26 +00:00
David Majnemer
643bef9333 InstCombine: Fix another infinite loop caused by visitFPTrunc
We would attempt to replace an frem's operand with the same operand.
This would cause InstCombine to think real work was done, causing
InstCombine to enter an infinite loop.

This fixes the second part of PR21576.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222265 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 22:06:45 +00:00
David Majnemer
063e54286c Revert "Revert r222040 because of bot failure."
This reverts commit r222203, reverting r222040 didn't end up turning the
bot green.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222261 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 21:30:02 +00:00
Chad Rosier
3980c542e6 [Reassociate] Rename local variable to not use same name as a member
variable. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222248 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 20:21:54 +00:00
Philip Reames
0814bd85dd Tweak EarlyCSE to recognize series of dead stores
EarlyCSE is giving up on the current instruction immediately when it recognizes that the current instruction makes a previous store trivially dead. There's no reason to do this. Once the previous store has been deleted, it's perfectly legal to remember the value of the current store (for value forwarding) and the fact the store occurred (it could be dead too!).

Reviewed by: Hal
Differential Revision: http://reviews.llvm.org/D6301



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222241 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 17:46:32 +00:00
David Majnemer
0ede3a2ae5 InstCombine: Fold away tautological masked compares
It is impossible for (x & INT_MAX) == 0 && x == INT_MAX to ever be true.

While this sort of reasoning should normally live in InstSimplify,
the machinery that derives this result is not trivial to split out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222230 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 09:31:41 +00:00
David Majnemer
2c906a4607 InstCombine: Clean up foldLogOpOfMaskedICmps
No functional change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222229 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 09:31:36 +00:00
Hans Wennborg
9ba744b089 SimplifyCFG: Range'ify some for-loops. No functional change.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222215 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 02:37:11 +00:00
David Majnemer
1ade0f0faa IndVarSimplify: Allow LFTR to fire more often
I added a pessimization in r217102 to prevent miscompiles when the
incremented induction variable was used in a comparison; it would be
poison.

Try to use the incremented induction variable more often when we can be
sure that the increment won't end in poison.

Differential Revision: http://reviews.llvm.org/D6222

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222213 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 02:20:58 +00:00
Manman Ren
8ce35351f8 Revert r222040 because of bot failure.
http://lab.llvm.org:8080/green/job/clang-Rlto_master/298/
Hopefully, bot will be green.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222203 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-18 00:33:22 +00:00
Juergen Ributzka
18db81a0ec [SimplifyCFG] Make the value type of the hole check bitmask a power-of-2.
When converting a switch to a lookup table we might have to generate a bitmaks
to encode and check for holes in the original switch statement.

The type of this mask depends on the number of switch statements, which can
result in illegal types for pretty much all architectures.

To avoid unnecessary type legalization and help FastISel this commit increases
the size of the bitmask to next power-of-2 value when necessary.

This fixes rdar://problem/18984639.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222168 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-17 19:39:56 +00:00
Chad Rosier
14915fe523 [Reassociate] As the expression tree is rewritten make sure the operands are
emitted in canonical form.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222142 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-17 16:33:50 +00:00
Chad Rosier
ae3738f4a7 [Reassociate] Canonicalize constants to RHS operand.
Fix a thinko where the RHS was already a constant.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222139 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-17 15:52:51 +00:00
Erik Eckstein
72a1394991 Optimize switch lookup tables with linear mapping.
This is a simple optimization for switch table lookup:
It computes the output value directly with an (optional) mul and add if there is a linear mapping between index and output.
Example:

int f1(int x) {
  switch (x) {
    case 0: return 10;
    case 1: return 11;
    case 2: return 12;
    case 3: return 13;
  }
  return 0;
}

generates:

define i32 @f1(i32 %x) #0 {
entry:
  %0 = icmp ult i32 %x, 4
  br i1 %0, label %switch.lookup, label %return

switch.lookup:
  %switch.offset = add i32 %x, 10
  ret i32 %switch.offset

return:
  ret i32 0
}



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222121 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-17 09:13:57 +00:00
Rafael Espindola
daa09d03ab Add back r222061 with a fix.
This adds back r222061, but now calls initializePAEvalPass from the correct
library to avoid link problems.

Original message:

Don't make assumptions about the name of private global variables.

Private variables are can be renamed, so it is not reliable to make
decisions on the name.

The name is also dropped by the assembler before getting to the
linker, so using the name causes a disconnect between how llvm makes a
decision (var name) and how the linker makes a decision (section it is
in).

This patch changes one case where we were looking at the variable name to use
the section instead.

Test tuning by Michael Gottesman.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222117 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-17 02:28:27 +00:00
Reid Kleckner
bfabc8f8c5 Revert "Don't make assumptions about the name of private global variables."
This reverts commit r222061.

It's causing linker errors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222077 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-15 02:03:53 +00:00
Rafael Espindola
e2eb8b632d Don't make assumptions about the name of private global variables.
Private variables are can be renamed, so it is not reliable to make
decisions on the name.

The name is also dropped by the assembler before getting to the
linker, so using the name causes a disconnect between how llvm makes a
decision (var name) and how the linker makes a decision (section it is
in).

This patch changes one case where we were looking at the variable name to use
the section instead.

Test tuning by Michael Gottesman.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222061 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 23:17:47 +00:00
David Majnemer
9019a6092d InstCombine: Fix infinite loop caused by visitFPTrunc
We would attempt to replace a fptrunc of an frem with an identical
fptrunc.  This would cause the new fptrunc to be added to the worklist.
Of course, this results in an infinite loop because we will keep
visiting the newly created fptruncs.

This fixes PR21576.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222040 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 21:21:15 +00:00
Chad Rosier
1523db7c64 Reapply r221924: "[GVN] Perform Scalar PRE on gep indices that feed loads before
doing Load PRE"

This commit updates the failing test in
Analysis/TypeBasedAliasAnalysis/gvn-nonlocal-type-mismatch.ll

The failing test is sensitive to the order in which we process loads.  This
version turns on the RPO traversal instead of the while DT traversal in GVN.
The new test code is functionally same just the order of loads that are
eliminated is swapped.

This new version also fixes an issue where GVN splits a critical edge and
potentially invalidate the RPO/DT iterator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222039 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 21:09:13 +00:00
David Blaikie
7ffaebf9da Remove redundant virtual on overriden functions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222023 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 19:06:36 +00:00
Chad Rosier
5c76b3d03e [Reassociate] Canonicalize the operands of all binary operators.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222008 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 17:09:19 +00:00
Chad Rosier
1298a29c64 [Reassociate] Canonicalize operands of vector binary operators.
Prior to this commit fmul and fadd binary operators were being canonicalized for
both scalar and vector versions.  We now canonicalize add, mul, and, or, and xor
vector instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222006 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 17:08:15 +00:00
Chad Rosier
7e61b1fb62 [Reassociate] Canonicalize constants to RHS operand.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222005 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 17:05:59 +00:00
Chad Rosier
1945dcff86 [Reassociate] Improve rank debug information. NFC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221999 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 15:01:38 +00:00
David Blaikie
677506434b Fix 80 cols caught by the linter...
We have a linter running in our build now?

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221957 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-14 00:41:42 +00:00
Duncan P. N. Exon Smith
f4742f4c84 IR: Make MDString::getName() private
Hide the fact that `MDString`'s string is stored in `Value::Name` --
that's going to change soon.  Update the only in-tree client that was
using it instead of `Value::getString()`.

Part of PR21532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221951 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-13 23:59:16 +00:00
Reid Kleckner
e094cca7f0 Use nullptr instead of NULL for variadic sentinels
Windows defines NULL to 0, which when used as an argument to a variadic
function, is not a null pointer constant. As a result, Clang's
-Wsentinel fires on this code. Using '0' would be wrong on most 64-bit
platforms, but both MSVC and Clang make it work on Windows. Sidestep the
issue with nullptr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221940 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-13 22:55:19 +00:00
Chad Rosier
7984fde2dc Revert "[GVN] Perform Scalar PRE on gep indices that feed loads before doing Load PRE."
This reverts commit r221924.  It appears the commit was a bit premature and is causing
bot failures that need further investigation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221939 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-13 22:54:59 +00:00
Chad Rosier
a9cc4e7e35 [GVN] Perform Scalar PRE on gep indices that feed loads before doing Load PRE.
Phabricator Revision: http://reviews.llvm.org/D6103
Patch by "Balaram Makam" <bmakam@codeaurora.org>!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221924 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-13 21:17:58 +00:00
Chad Rosier
ddf4026dd8 [Reassociate] Update comment. NFC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221894 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-13 15:40:20 +00:00
Ahmed Bougacha
f9e1e56ea1 Add fortified (__*_chk) library functions to TLI (NFC)
One of them (__memcpy_chk) was already there, the others were checked
by comparing function names.
Note that the fortified libfuncs are now part of TLI, but are always
available, because they aren't generated, only optimized into the
non-checking versions.

Differential Revision: http://reviews.llvm.org/D6179


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221817 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-12 21:23:34 +00:00
Jingyue Wu
83c8e732dd Disable indvar widening if arithmetics on the wider type are more expensive
Summary:
Reapply r221772. The old patch breaks the bot because the @indvar_32_bit test
was run whether NVPTX was enabled or not.

IndVarSimplify should not widen an indvar if arithmetics on the wider
indvar are more expensive than those on the narrower indvar. For
instance, although NVPTX64 treats i64 as a legal type, an ADD on i64 is
twice as expensive as that on i32, because the hardware needs to
simulate a 64-bit integer using two 32-bit integers.

Split from D6188, and based on D6195 which adds NVPTXTargetTransformInfo.

Fixes PR21148.

Test Plan:
Added @indvar_32_bit that verifies we do not widen an indvar if the arithmetics
on the wider type are more expensive. This test is run only when NVPTX is
enabled.

Reviewers: jholewinski, eliben, meheff, atrick

Reviewed By: atrick

Subscribers: jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D6196



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221799 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-12 18:09:15 +00:00
Sanjay Patel
04a3fdf788 remove function names from comments; NFC
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221798 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-12 18:07:42 +00:00
Jingyue Wu
ee709fe497 Reverts r221772 which fails tests
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221773 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-12 07:19:25 +00:00
Jingyue Wu
69adc159ee Disable indvar widening if arithmetics on the wider type are more expensive
Summary:
IndVarSimplify should not widen an indvar if arithmetics on the wider
indvar are more expensive than those on the narrower indvar. For
instance, although NVPTX64 treats i64 as a legal type, an ADD on i64 is
twice as expensive as that on i32, because the hardware needs to
simulate a 64-bit integer using two 32-bit integers.

Split from D6188, and based on D6195 which adds NVPTXTargetTransformInfo.

Fixes PR21148.

Test Plan:
Added @indvar_32_bit that verifies we do not widen an indvar if the arithmetics
on the wider type are more expensive.

Reviewers: jholewinski, eliben, meheff, atrick

Reviewed By: atrick

Subscribers: jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D6196

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221772 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-12 06:58:45 +00:00
Bill Schmidt
fc22bfd921 [PowerPC] Add vec_vsx_ld and vec_vsx_st intrinsics
This patch enables the vec_vsx_ld and vec_vsx_st intrinsics for
PowerPC, which provide programmer access to the lxvd2x, lxvw4x,
stxvd2x, and stxvw4x instructions.

New LLVM intrinsics are provided to represent these four instructions
in IntrinsicsPowerPC.td.  These are patterned after the similar
intrinsics for lvx and stvx (Altivec).  In PPCInstrVSX.td, these
intrinsics are tied to the code gen patterns, with additional patterns
to allow plain vanilla loads and stores to still generate these
instructions.

At -O1 and higher the intrinsics are immediately converted to loads
and stores in InstCombineCalls.cpp.  This will open up more
optimization opportunities while still allowing the correct
instructions to be generated.  (Similar code exists for aligned
Altivec loads and stores.)

The new intrinsics are added to the code that checks for consecutive
loads and stores in PPCISelLowering.cpp, as well as to
PPCTargetLowering::getTgtMemIntrinsic().

There's a new test to verify the correct instructions are generated.
The loads and stores tend to be reordered, so the test just counts
their number.  It runs at -O2, as it's not very effective to test this
at -O0, when many unnecessary loads and stores are generated.

I ended up having to modify vsx-fma-m.ll.  It turns out this test case
is slightly unreliable, but I don't know a good way to prevent
problems with it.  The xvmaddmdp instructions read and write the same
register, which is one of the multiplicands.  Commutativity allows
either to be chosen.  If the FMAs are reordered differently than
expected by the test, the register assignment can be different as a
result.  Hopefully this doesn't change often.

There is a companion patch for Clang.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221767 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-12 04:19:40 +00:00
Chad Rosier
7ad8db4cbb [Reassociate] Canonicalize negative constants out of expressions.
Add support for FDiv, which was regressed by the previous commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221738 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-11 23:36:42 +00:00
Philip Reames
a03cda02ab Canonicalize an assume(load != null) into !nonnull metadata
We currently have two ways of informing the optimizer that the result of a load is never null: metadata and assume. This change converts the second in to the former. This avoids a need to implement optimizations using both forms.

We should probably extend this basic idea to metadata of other forms; in particular, range metadata. We view is that assumes should be considered a "last resort" for when there isn't a more canonical way to represent something.

Reviewed by: Hal
Differential Revision: http://reviews.llvm.org/D5951



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221737 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-11 23:33:19 +00:00