Commit Graph

4990 Commits

Author SHA1 Message Date
Gerolf Hoflehner
049a087d3f Suppress inlining when the block address is taken
Inlining functions with block addresses can cause many problem and requires a
rich infrastructure to support including escape analysis.  At this point the
safest approach to address these problems is by blocking inlining from
happening.

Background:
There have been reports on Ruby segmentation faults triggered by inlining
functions with block addresses like

//Ruby code snippet
vm_exec_core() {
    finish_insn_seq_0 = &&INSN_LABEL_finish;
    INSN_LABEL_finish:
      ;
}

This kind of scenario can also happen when LLVM picks a subset of blocks for
inlining, which is the case with the actual code in the Ruby environment.

LLVM suppresses inlining for such functions when there is an indirect branch.
The attached patch does so even when there is no indirect branch.  Note that
user code like above would not make much sense: using the global for jumping
across function boundaries would be illegal.

Why was there a segfault:

In the snipped above the block with the label is recognized as dead So it is
eliminated. Instead of a block address the cloner stores a constant (sic!) into
the global resulting in the segfault (when the global is used in a goto).

Why had it worked in the past then:

By luck. In older versions vm_exec_core was also inlined but the label address
used was the block label address in vm_exec_core.  So the global jump ended up
in the original function rather than in the caller which accidentally happened
to work.

Test case ./tools/clang/test/CodeGen/indirect-goto.c will fail as a result
of this commit.

rdar://17245966



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212077 91177308-0d34-0410-b5e6-96231b3b80d8
2014-07-01 00:19:34 +00:00
Alp Toker
8dd8d5c2b2 Revert "Introduce a string_ostream string builder facilty"
Temporarily back out commits r211749, r211752 and r211754.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211814 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-26 22:52:05 +00:00
Dinesh Dwivedi
c2b11baf5f This patch removed duplicate code for matching patterns
which are now handled in SimplifyUsingDistributiveLaws() 
(after r211261)

Differential Revision: http://reviews.llvm.org/D4253



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211768 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-26 08:57:33 +00:00
Alp Toker
45f166017c MSVC build fix following r211749
Avoid strndup()

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211752 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-26 00:25:41 +00:00
Alp Toker
2559070422 Introduce a string_ostream string builder facilty
string_ostream is a safe and efficient string builder that combines opaque
stack storage with a built-in ostream interface.

small_string_ostream<bytes> additionally permits an explicit stack storage size
other than the default 128 bytes to be provided. Beyond that, storage is
transferred to the heap.

This convenient class can be used in most places an
std::string+raw_string_ostream pair or SmallString<>+raw_svector_ostream pair
would previously have been used, in order to guarantee consistent access
without byte truncation.

The patch also converts much of LLVM to use the new facility. These changes
include several probable bug fixes for truncated output, a programming error
that's no longer possible with the new interface.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211749 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-26 00:00:48 +00:00
Duncan P. N. Exon Smith
856361cb06 Support: Move class ScaledNumber
ScaledNumber has been cleaned up enough to pull out of BFI now.  Still
work to do there (tests for shifting, bloated printing code, etc.), but
it seems clean enough for its new home.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211562 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-24 00:38:09 +00:00
Duncan P. N. Exon Smith
6ecab5a5b1 BFI: Un-floatify more language
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211561 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-24 00:26:13 +00:00
Duncan P. N. Exon Smith
784bb5992a Support: Extract ScaledNumbers::MinScale and MaxScale
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211558 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-24 00:15:19 +00:00
Duncan P. N. Exon Smith
747b62f119 BFI: Change language from "exponent" to "scale"
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211557 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-23 23:57:12 +00:00
Duncan P. N. Exon Smith
7c21d709a3 BFI: Rename UnsignedFloat => ScaledNumber
A lot of the docs and API are out of date, but I'll leave that for a
separate commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211555 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-23 23:36:17 +00:00
Benjamin Kramer
b7f1fb47e6 SCEVExpander: Fold constant PHIs harder. The logic below only understands proper IVs.
PR20093.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211433 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-21 11:47:18 +00:00
Richard Trieu
7921239c41 Add back functionality removed in r210497.
Instead of asserting, output a message stating that a null pointer was found.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211430 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-21 02:43:02 +00:00
Duncan P. N. Exon Smith
67291098a6 Support: Write ScaledNumber::getQuotient() and getProduct()
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211409 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-20 21:47:47 +00:00
Jingyue Wu
e4d0a5ec18 [ValueTracking] Extend range metadata to call/invoke
Summary:
With this patch, range metadata can be added to call/invoke including
IntrinsicInst. Previously, it could only be added to load.

Rename computeKnownBitsLoad to computeKnownBitsFromRangeMetadata because
range metadata is not only used by load.

Update the language reference to reflect this change.

Test Plan:
Add several tests in range-2.ll to confirm the verifier is happy with
having range metadata on call/invoke.

Add two tests in AddOverFlow.ll to confirm annotating range metadata to
call/invoke can benefit InstCombine.

Reviewers: meheff, nlewycky, reames, hfinkel, eliben

Reviewed By: eliben

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D4187

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211281 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-19 16:50:16 +00:00
Nick Lewycky
fe3a219355 Move optimization of some cases of (A & C1)|(B & C2) from instcombine to instsimplify. Patch by Rahul Jain, plus some last minute changes by me -- you can blame me for any bugs.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211252 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-19 03:51:46 +00:00
Nick Lewycky
650b6ea893 Make instsimplify's analysis of icmp eq/ne use computeKnownBits to determine whether the icmp is always true or false. Patch by Suyog Sarda!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211251 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-19 03:35:49 +00:00
Richard Trieu
f31ecd3927 Removing an "if (!this)" check from two print methods. The condition will
never be true in a well-defined context.  The checking for null pointers
has been moved into the caller logic so it does not rely on undefined behavior.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210497 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-09 22:53:16 +00:00
Alp Toker
5396370ebb Remove old fenv.h workaround for a historic clang driver bug
Tested and works fine with clang using libstdc++.

All indications are that this was fixed some time ago and isn't a problem with
any clang version we support.

I've added a note in PR6907 which is still open for some reason.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210485 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-09 19:00:52 +00:00
Alp Toker
f4cf404837 Fold FEnv.h into the implementation
Support headers shouldn't use config.h definitions, and they should never be
undefined like this.

ConstantFolding.cpp was the only user of this facility and already includes
config.h for other math features, so it makes sense to move the checks there at
point of use.

(The implicit config.h was also quite dangerous -- removing the FEnv.h include
would have silently disabled math constant folding without causing any tests to
fail. Need to investigate -Wundef once the cleanup is done.)

This eliminates the last config.h include from LLVM headers, paving the way for
more consistent configuration checks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210483 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-09 18:28:53 +00:00
Tobias Grosser
5e66eea5ba ScalarEvolution: Derive element size from the type of the loaded element
Before, we where looking at the size of the pointer type that specifies the
location from which to load the element. This did not make any sense at all.

This change fixes a bug in the delinearization where we failed to delinerize
certain load instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210435 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-08 19:21:20 +00:00
Tom Roeder
5d0f7af3dc Add a new attribute called 'jumptable' that creates jump-instruction tables for functions marked with this attribute.
It includes a pass that rewrites all indirect calls to jumptable functions to pass through these tables.

This also adds backend support for generating the jump-instruction tables on ARM and X86.
Note that since the jumptable attribute creates a second function pointer for a
function, any function marked with jumptable must also be marked with unnamed_addr.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210280 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-05 19:29:43 +00:00
Rafael Espindola
cfee6c49ea Add a Constant version of stripPointerCasts.
Thanks to rnk for the suggestion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210205 91177308-0d34-0410-b5e6-96231b3b80d8
2014-06-04 19:01:48 +00:00
Sebastian Pop
20b6ed3c9c implement missing SCEVDivision case
without this case we would end on an infinite recursion: the remainder is zero,
so Numerator - Remainder is equal to Numerator and so we would recursively ask
for the division of Numerator by Denominator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209838 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-29 19:44:09 +00:00
Sebastian Pop
e741924230 fail to find dimensions when ElementSize is nullptr
when ScalarEvolution::getElementSize returns nullptr it is safe to early return
in ScalarEvolution::findArrayDimensions such that we avoid later problems when
we try to divide the terms by ElementSize.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209837 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-29 19:44:05 +00:00
Sanjay Patel
f558122fe5 test check-in: added missing parenthesis in comment
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209763 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-28 19:03:33 +00:00
Sebastian Pop
5013d1d5e4 avoid type mismatch when building SCEVs
This is a corner case I have stumbled upon when dealing with ARM64 type
conversions. I was not able to extract a testcase for the community codebase to
fail on. The patch conservatively discards a division that would have ended up
in an ICE due to a type mismatch when building a multiply expression. I have
also added code to a place that builds add expressions and in which we should be
careful not to pass in operands of different types.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209694 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-27 22:42:00 +00:00
Sebastian Pop
bf48d8ae51 do not use the GCD to compute the delinearization strides
We do not need to compute the GCD anymore after we removed the constant
coefficients from the terms: the terms are now all parametric expressions and
there is no need to recognize constant terms that divide only a subset of the
terms. We only rely on the size of the terms, i.e., the number of operands in
the multiply expressions, to sort the terms and recognize the parametric
dimensions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209693 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-27 22:41:56 +00:00
Sebastian Pop
79facc9e29 remove BasePointer before delinearizing
No functional change is intended: instead of relying on the delinearization to
come up with the base pointer as a remainder of the divisions in the
delinearization, we just compute it from the array access and use that value.
We substract the base pointer from the SCEV to be delinearized and that
simplifies the work of the delinearizer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209692 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-27 22:41:51 +00:00
Sebastian Pop
421b2c571c remove constant terms
The delinearization is needed only to remove the non linearity induced by
expressions involving multiplications of parameters and induction variables.
There is no problem in dealing with constant times parameters, or constant times
an induction variable.

For this reason, the current patch discards all constant terms and multipliers
before running the delinearization algorithm on the terms. The only thing
remaining in the term expressions are parameters and multiply expressions of
parameters: these simplified term expressions are passed to the array shape
recognizer that will not recognize constant dimensions anymore: these will be
recognized as different strides in parametric subscripts.

The only important special case of a constant dimension is the size of elements.
Instead of relying on the delinearization to infer the size of an element,
compute the element size from the base address type. This is a much more precise
way of computing the element size than before, as we would have mixed together
the size of an element with the strides of the innermost dimension.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209691 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-27 22:41:45 +00:00
Michael Zolotukhin
90e79a50bb Some cleanup for r209568.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209634 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-26 14:49:46 +00:00
Michael Zolotukhin
45788be6e2 Implement sext(C1 + C2*X) --> sext(C1) + sext(C2*X) and
sext{C1,+,C2} --> sext(C1) + sext{0,+,C2} transformation in Scalar
Evolution.

That helps SLP-vectorizer to recognize consecutive loads/stores.

<rdar://problem/14860614>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209568 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-24 08:09:57 +00:00
Andrew Trick
ab0d042a74 Fix and improve SCEV ComputeBackedgeTankCount.
This is a follow-up to r209358: PR19799: Indvars miscompile due to an
incorrect max backedge taken count from SCEV.

That fix was incomplete as pointed out by Arnold and Michael Z. The
code was also too confusing. It needed a careful rewrite with more
unit tests. This version will also happen to optimize more cases.

<rdar://17005101> PR19799: Indvars miscompile...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209545 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-23 19:47:13 +00:00
Justin Bogner
e318ce611f ScalarEvolution: Fix handling of AddRecs in isKnownPredicate
ScalarEvolution::isKnownPredicate() can wrongly reduce a comparison
when both the LHS and RHS are SCEVAddRecExprs. This checks that both
LHS and RHS are guarded in the case when both are SCEVAddRecExprs.

The test case is against indvars because I could not find a way to
directly test SCEV.

Patch by Sanjay Patel!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209487 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-23 00:06:56 +00:00
Andrew Trick
facca6e3f3 Fix a bug in SCEV's backedge taken count computation from my prior fix in Jan.
This has to do with the trip count computation for loops with multiple
exits, which is quite subtle. Most passes just ask for a single trip
count number, so we must be conservative assuming any exit could be
taken.  Normally, we rely on the "exact" trip count, which was
correctly given as "unknown". However, SCEV also gives a "max"
back-edge taken count. The loops max BE taken count is conservatively
a maximum over the max of each exit's non-exiting iterations
count. Note that some exit tests can be skipped so the max loop
back-edge taken count can actually exceed the max non-exiting
iterations for some exits. However, when we know the loop *latch*
cannot be skipped, we can directly use its max taken count
disregarding other exits. I previously took the minimum here without
checking whether the other exit could be skipped. The correct, and
simpler thing to do here is just to directly use the loop latch's max
non-exiting iterations as the loops max back-edge count.

In the problematic test case, the first loop exit had a max of zero
non-exiting iterations, but could be skipped. The loop latch was known
not to be skipped but had max of one non-exiting iteration. We
incorrectly claimed the loop back-edge could be taken zero times, when
it is actually taken one time.

Fixes Loop %for.body.i: <multiple exits> Unpredictable backedge-taken count.
Loop %for.body.i: max backedge-taken count is 1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209358 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-22 00:37:03 +00:00
Eric Christopher
68c7a1cb98 Clean up language and grammar.
Based on a patch by jfcaron3@gmail.com!
PR19806

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209216 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-20 17:11:11 +00:00
Nick Lewycky
4bf804fe0d Teach isKnownNonNull that a nonnull return is not null. Add a test for this case as well as the case of a nonnull attribute (already handled but not tested).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209193 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-20 05:13:21 +00:00
Nick Lewycky
fe47ebfad3 Add 'nonnull', a new parameter and return attribute which indicates that the pointer is not null. Instcombine will elide comparisons between these and null. Patch by Luqman Aden!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209185 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-20 01:23:40 +00:00
Peter Collingbourne
20a6a27bea Check the alwaysinline attribute on the call as well as on the caller.
Differential Revision: http://reviews.llvm.org/D3815

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209150 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-19 18:25:54 +00:00
David Majnemer
3258443195 InstSimplify: Improve handling of ashr/lshr
Summary:
Analyze the range of values produced by ashr/lshr cst, %V when it is
being used in an icmp.

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3774

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209000 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-16 17:14:03 +00:00
David Majnemer
7a2ed26563 InstSimplify: Optimize using dividend in sdiv
Summary:
The dividend in an sdiv tells us the largest and smallest possible
results.  Use this fact to optimize comparisons against an sdiv with a
constant dividend.

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3795

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208999 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-16 16:57:04 +00:00
Juergen Ributzka
9bc1b73c9e Add C API for thread yielding callback.
Sometimes a LLVM compilation may take more time then a client would like to
wait for. The problem is that it is not possible to safely suspend the LLVM
thread from the outside. When the timing is bad it might be possible that the
LLVM thread holds a global mutex and this would block any progress in any other
thread.

This commit adds a new yield callback function that can be registered with a
context. LLVM will try to yield by calling this callback function, but there is
no guaranteed frequency. LLVM will only do so if it can guarantee that
suspending the thread won't block any forward progress in other LLVM contexts
in the same process.

Once the client receives the call back it can suspend the thread safely and
resume it at another time.

Related to <rdar://problem/16728690>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208945 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-16 02:33:15 +00:00
Jay Foad
b7ba5c2e2e Instead of littering asserts throughout the code after every call to
computeKnownBits, consolidate them into one assert at the end of
computeKnownBits itself.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208876 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-15 12:12:55 +00:00
Chandler Carruth
ca323cf916 Teach the constant folder to look through bitcast constant expressions
much more effectively when trying to constant fold a load of a constant.
Previously, we only handled bitcasts by trying to find a totally generic
byte representation of the constant and use that. Now, we look through
the bitcast to see what constant we might fold the load into, and then
try to form a constant expression cast of the found value that would be
equivalent to loading the value.

You might wonder why on earth this actually matters. Well, turns out
that the Itanium ABI causes us to create a single array for a vtable
where the first elements are virtual base offsets, followed by the
virtual function pointers. Because the array is homogenous the element
type is consistently i8* and we inttoptr the virtual base offsets into
the initial elements.

Then constructors bitcast these pointers to i64 pointers prior to
loading them. Boom, no more constant folding of virtual base offsets.
This is the first fix to LLVM to address the *insane* performance Eric
Niebler discovered with Clang on his range comprehensions[1]. There is
more to come though, this doesn't *really* fix the problem fully.

[1]: http://ericniebler.com/2014/04/27/range-comprehensions/

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208856 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-15 09:56:28 +00:00
Alp Toker
727273b11c Fix typos
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208839 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-15 01:52:21 +00:00
Jay Foad
6b543713a2 Rename ComputeMaskedBits to computeKnownBits. "Masked" has been
inappropriate since it lost its Mask parameter in r154011.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208811 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-14 21:14:37 +00:00
David Majnemer
cd237ed585 InstSimplify: Optimize signed icmp of -(zext V)
Summary:
We know that -(zext V) will always be <= zero, simplify signed icmps
that have these.

Uncovered using http://www.cs.utah.edu/~regehr/souper/

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3754

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208809 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-14 20:16:28 +00:00
Jay Foad
5fa4d1cd1a Update the comments for ComputeMaskedBits, which lost its Mask parameter
in r154011.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208757 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-14 08:00:07 +00:00
Sebastian Pop
d2b27bba87 use nullptr instead of NULL
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208622 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-12 20:11:01 +00:00
Sebastian Pop
2f5f1c2ccb do not assert when delinearization fails
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208615 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-12 19:01:53 +00:00
Sebastian Pop
d9673ebd34 use isZero()
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208614 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-12 19:01:49 +00:00