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Commit Graph

166144 Commits

Author SHA1 Message Date
Sanjay Patel
3493a214af [Reassociate] add test for missing FP constant analysis; NFC
llvm-svn: 336208
2018-07-03 15:56:04 +00:00
Teresa Johnson
ba5f496171 Rename lazy initialization functions to reflect behavior (NFC)
Suggested in review for D48698.

llvm-svn: 336207
2018-07-03 15:52:57 +00:00
Sander de Smalen
2fbefa55ad [AArch64][SVE] Asm: Support for FMUL (indexed)
Unpredicated FP-multiply of SVE vector with a vector-element given by
vector[index], for example:

  fmul z0.s, z1.s, z2.s[0]

which performs an unpredicated FP-multiply of all 32-bit elements in
'z1' with the first element from 'z2'.

This patch adds restricted register classes for SVE vectors:
  ZPR_3b (only z0..z7 are allowed)  - for indexed vector of 16/32-bit elements.
  ZPR_4b (only z0..z15 are allowed) - for indexed vector of 64-bit elements.

Reviewers: rengolin, fhahn, SjoerdMeijer, samparker, javed.absar

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D48823

llvm-svn: 336205
2018-07-03 15:31:04 +00:00
Sander de Smalen
d14899902f [AArch64][SVE] Asm: Support for predicated unary operations.
The patch includes support for the following instructions:

       ABS z0.h, p0/m, z0.h
       NEG z0.h, p0/m, z0.h

  (S|U)XTB z0.h, p0/m, z0.h
  (S|U)XTB z0.s, p0/m, z0.s
  (S|U)XTB z0.d, p0/m, z0.d

  (S|U)XTH z0.s, p0/m, z0.s
  (S|U)XTH z0.d, p0/m, z0.d

  (S|U)XTW z0.d, p0/m, z0.d

llvm-svn: 336204
2018-07-03 14:57:48 +00:00
Simon Pilgrim
6acb553e8a [DAGCombiner] visitSDIV - Permit MIN_SIGNED_VALUE in pow2 vector codegen
Now that D45806 has landed, we can re-enable support for MIN_SIGNED_VALUE in the sdiv by pow2-constant code

llvm-svn: 336198
2018-07-03 14:11:32 +00:00
Sanjay Patel
1321d2af68 [InstCombine] fold shuffle-with-binop and common value
This is the last significant change suggested in PR37806:
https://bugs.llvm.org/show_bug.cgi?id=37806#c5
...though there are several follow-ups noted in the code comments 
in this patch to complete this transform.

It's possible that a binop feeding a select-shuffle has been eliminated 
by earlier transforms (or the code was just written like this in the 1st 
place), so we'll fail to match the patterns that have 2 binops from: 
D48401, 
D48678, 
D48662, 
D48485.

In that case, we can try to materialize identity constants for the remaining
binop to fill in the "ghost" lanes of the vector (where we just want to pass 
through the original values of the source operand).

I added comments to ConstantExpr::getBinOpIdentity() to show planned follow-ups. 
For now, we only handle the 5 commutative integer binops (add/mul/and/or/xor).

Differential Revision: https://reviews.llvm.org/D48830

llvm-svn: 336196
2018-07-03 13:44:22 +00:00
Sam Parker
3f68940249 [ARM][NFC] Refactor sequential access for DSP
With a view to support parallel operations that have their results
stored to memory, refactor the consecutive access helper out so it
could support stores instructions.

Differential Revision: https://reviews.llvm.org/D48872

llvm-svn: 336195
2018-07-03 12:44:16 +00:00
Bjorn Pettersson
d6a0222d34 [IR] Strip trailing whitespace. NFC
llvm-svn: 336194
2018-07-03 12:39:52 +00:00
Sjoerd Meijer
765bfbdcbd [AArch64] Armv8.4-A: system registers
This adds the following system registers:
- RAS registers,
- MPAM registers,
- Activitiy monitor registers,
- Trace Extension registers,
- Timing insensitivity of data processing instructions,
- Enhanced Support for Nested Virtualization.

Differential Revision: https://reviews.llvm.org/D48871

llvm-svn: 336193
2018-07-03 12:09:20 +00:00
Hans Wennborg
24eaa76313 build_llvm_package.bat: Re-try the build steps
The build on Windows has been extra flaky recently; retrying helps.

llvm-svn: 336192
2018-07-03 11:30:01 +00:00
Bjorn Pettersson
b45e047d7d [DebugInfo] Corrections for salvageDebugInfo
Summary:
When salvaging a dbg.declare/dbg.addr we should not add
DW_OP_stack_value to the DIExpression
(see test/Transforms/InstCombine/salvage-dbg-declare.ll).

Consider this example
  %vla = alloca i32, i64 2
  call void @llvm.dbg.declare(metadata i32* %vla, metadata !1, metadata !DIExpression())

Instcombine will turn it into
  %vla1 = alloca [2 x i32]
  %vla1.sub = getelementptr inbounds [2 x i32], [2 x i32]* %vla, i64 0, i64 0
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1.sub, metadata !19, metadata !DIExpression())

If the GEP can be eliminated, then the dbg.declare will be salvaged
and we should get
  %vla1 = alloca [2 x i32]
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1, metadata !19, metadata !DIExpression())

The problem was that salvageDebugInfo did not recognize dbg.declare
as being indirect (%vla1 points to the value, it does not hold the
value), so we incorrectly got
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1, metadata !19, metadata !DIExpression(DW_OP_stack_value))

I also made sure that llvm::salvageDebugInfo and
DIExpression::prependOpcodes do not add DW_OP_stack_value to
the DIExpression in case no new operands are added to the
DIExpression. That way we avoid to, unneccessarily, turn a
register location expression into an implicit location expression
in some situations (see test11 in test/Transforms/LICM/sinking.ll).

Reviewers: aprantl, vsk

Reviewed By: aprantl, vsk

Subscribers: JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D48837

llvm-svn: 336191
2018-07-03 11:29:00 +00:00
Benjamin Kramer
82b5d98341 Revert "[X86][SSE] Blend any v8i16/v4i32 shift with 2 shift unique values"
This reverts commit r336113. It causes crashes.

llvm-svn: 336189
2018-07-03 11:15:17 +00:00
John Brawn
81942f0468 [llvm-exegesis] Adjust AArch64 unit test
The signature of setRegToConstant changed in r336171, so adjust the AArch64
unit test in a similar way to how the X86 unit test was changed in that commit.

llvm-svn: 336188
2018-07-03 10:52:20 +00:00
John Brawn
11da94da63 [llvm-exegesis] Add an AArch64 target
The target does just enough to be able to run llvm-exegesis in latency mode for
at least some opcodes.

Differential Revision: https://reviews.llvm.org/D48780

llvm-svn: 336187
2018-07-03 10:10:29 +00:00
Sander de Smalen
bc76d6bc5b [AArch64][SVE] Asm: Support for saturing ADD/SUB instructions.
The variants added are:
    signed Saturating ADD/SUB (immediate)  e.g. sqadd z0.h, z0.h, #42
  unsigned Saturating ADD/SUB (immediate)  e.g. uqadd z0.h, z0.h, #42
    signed Saturating ADD/SUB (vectors)    e.g. sqadd z0.h, z0.h, z1.h
  unsigned Saturating ADD/SUB (vectors)    e.g. uqadd z0.h, z0.h, z1.h

llvm-svn: 336186
2018-07-03 09:48:22 +00:00
Petar Jovanovic
e27e377ca1 [MIPS GlobalISel] Lower arguments using stack
Lower more than 4 arguments using stack. This patch targets MIPS32.
It supports only functions with arguments of type i32.

Patch by Petar Avramovic.

Differential Revision: https://reviews.llvm.org/D47934

llvm-svn: 336185
2018-07-03 09:31:48 +00:00
Chandler Carruth
a61218ea75 [PM/LoopUnswitch] Fix PR37651 by correctly invalidating SCEV when
unswitching loops.

Original patch trying to address this was sent in D47624, but that
didn't quite handle things correctly. There are two key principles used
to select whether and how to invalidate SCEV-cached information about
loops:

1) We must invalidate any info SCEV has cached before unswitching as we
   may change (or destroy) the loop structure by the act of unswitching,
   and make it hard to recover everything we want to invalidate within
   SCEV.

2) We need to invalidate all of the loops whose CFGs are mutated by the
   unswitching. Notably, this isn't the *entire* loop nest, this is
   every loop contained by the outermost loop reached by an exit block
   relevant to the unswitch.

And we need to do this even when doing trivial unswitching.

I've added more focused tests that directly check that SCEV starts off
with imprecise information and after unswitching (and simplifying
instructions) re-querying SCEV will produce precise information. These
tests also specifically work to check that an *outer* loop's information
becomes precise.

However, the testing here is still a bit imperfect. Crafting test cases
that reliably fail to be analyzed by SCEV before unswitching and succeed
afterward proved ... very, very hard. It took me several hours and
careful work to build these, and I'm not optimistic about necessarily
coming up with more to cover more elaborate possibilities. Fortunately,
the code pattern we are testing here in the pass is really
straightforward and reliable.

Thanks to Max Kazantsev for the initial work on this as well as the
review, and to Hal Finkel for helping me talk through approaches to test
this stuff even if it didn't come to much.

Differential Revision: https://reviews.llvm.org/D47624

llvm-svn: 336183
2018-07-03 09:13:27 +00:00
Sander de Smalen
3392be5c6f [AArch64][SVE] Asm: Support for vector element FP compare.
Contains the following variants:

- Compare with (elements from) other vector
  instructions: fcmeq, fcmgt, fcmge, fcmne, fcmuo.
  aliases: fcmle, fcmlt.

  e.g. fcmle   p0.h, p0/z, z0.h, z1.h => fcmge p0.h, p0/z, z1.h, z0.h

- Compare absolute values with (absolute values from) other vector.
  instructions: facge, facgt.
  aliases: facle, faclt.

  e.g. facle   p0.h, p0/z, z0.h, z1.h => facge   p0.h, p0/z, z1.h, z0.h

- Compare vector elements with #0.0
  instructions: fcmeq, fcmgt, fcmge, fcmle, fcmlt, fcmne.

  e.g. fcmle   p0.h, p0/z, z0.h, #0.0

llvm-svn: 336182
2018-07-03 09:07:23 +00:00
Chandler Carruth
bccbda628d [ADT] Disable the single callback optimization on Windows.
It appears that the function pointer we use there isn't reliably 4-byte
aligned. I have no idea why or how we could correct this, so for now we
just regress the Windows performance some.

Someone with access to Windows could try working on a fix. At the very
least we could use a double indirection rather than a table, but maybe
there is some way to fully restore this optimization. I don't want to
play too much with this when I don't have access to the platform and
this at least should restore the last bots.

llvm-svn: 336178
2018-07-03 08:19:10 +00:00
Shiva Chen
95e2a3f024 [DebugInfo] Fix PR37395.
DbgLabelInst has no address as its operands.

Differential Revision: https://reviews.llvm.org/D46738

Patch by Hsiangkai Wang.

llvm-svn: 336176
2018-07-03 07:56:04 +00:00
Chandler Carruth
a02b81d85f [Support] This sanity check in the test only works with certain versions
of libstdc++, not just certain versions of GCC. The original macros
broke when using Clang + libstdc++4.9 sadly.

Sadly, testing for versions of libstdc++ has been extremely problematic
in the past, so I'm just narrowing this down to Windows and when using
libc++ as that seems at least very unlikely to keep build bots broken.

llvm-svn: 336174
2018-07-03 07:51:01 +00:00
Max Kazantsev
e6a4692668 [InstCombine] Delay foldICmpUsingKnownBits until simple transforms are done
This patch changes order of transform in InstCombineCompares to avoid
performing transforms based on ranges which produce complex bit arithmetics
before more simple things (like folding with constants) are done. See PR37636
for the motivating example.

Differential Revision: https://reviews.llvm.org/D48584
Reviewed By: spatel, lebedev.ri

llvm-svn: 336172
2018-07-03 06:23:57 +00:00
Clement Courbet
ea6e30ac41 [llvm-exegesis] ExegisX86Target::setRegToConstant() should depend on the subtarget features.
Summary: This fixes PR38008.

Reviewers: gchatelet, RKSimon

Subscribers: tschuett, craig.topper, llvm-commits

Differential Revision: https://reviews.llvm.org/D48820

llvm-svn: 336171
2018-07-03 06:17:05 +00:00
Chandler Carruth
9fa2159032 [ADT] Try to work around a crash in MSVC.
Putting `sizeof(T) <= 16` into the parameter of a `std::conditional`
causes every version of MSVC I've tried to crash:

  https://godbolt.org/g/eqVULL

Really frustrating, but an extra layer of indirection through an
instantiated type gives a working way to access this computed constant.

llvm-svn: 336170
2018-07-03 05:46:20 +00:00
Craig Topper
a8d96c712a [X86] Add avx512vl command line to break-false-dep.ll
llvm-svn: 336169
2018-07-03 04:43:49 +00:00
Chandler Carruth
3b0beec122 [ADT] Switch another place to llvm::is_trivially_move_constructible.
I missed this the first time around, sorry.

llvm-svn: 336166
2018-07-03 04:07:26 +00:00
Jakub Kuderski
bb148a0677 Reappl "[Dominators] Add the DomTreeUpdater class"
Summary:
This patch is the first in a series of patches related to the [[ http://lists.llvm.org/pipermail/llvm-dev/2018-June/123883.html | RFC - A new dominator tree updater for LLVM ]].

This patch introduces the DomTreeUpdater class, which provides a cleaner API to perform updates on available dominator trees (none, only DomTree, only PostDomTree, both) using different update strategies (eagerly or lazily) to simplify the updating process.

—Prior to the patch—

   - Directly calling update functions of DominatorTree updates the data structure eagerly while DeferredDominance does updates lazily.
   - DeferredDominance class cannot be used when a PostDominatorTree also needs to be updated.
   - Functions receiving DT/DDT need to branch a lot which is currently necessary.
   - Functions using both DomTree and PostDomTree need to call the update function separately on both trees.
   - People need to construct an additional DeferredDominance class to use functions only receiving DDT.

—After the patch—

Patch by Chijun Sima <simachijun@gmail.com>.

Reviewers: kuhar, brzycki, dmgreen, grosser, davide

Reviewed By: kuhar, brzycki

Author: NutshellySima

Subscribers: vsk, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D48383

llvm-svn: 336163
2018-07-03 02:06:23 +00:00
Erik Pilkington
45cd87da32 Revert r336159, r336157. Some bots failed on qualified std::max_align_t, and other on unqualified max_align_t.
I'll take another stab at this tomorrow. Any ideas for fixing this would be appreciated!

http://lab.llvm.org:8011/builders/lld-x86_64-darwin13/builds/23071/steps/build_Lld/logs/stdio
http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/11185/steps/build-stage1-compiler/logs/stdio

llvm-svn: 336162
2018-07-03 01:30:53 +00:00
Chandler Carruth
a37bbe946c [Support] Fix llvm::unique_function when building with GCC 4.9 by
introducing llvm::trivially_{copy,move}_constructible type traits.

This uses a completely portable implementation of these traits provided
by Richard Smith. You can see it on compiler explorer in all its glory:

  https://godbolt.org/g/QEDZjW

I have transcribed it, clang-formatted it, added some comments, and made
the tests fit into a unittest file.

I have also switched llvm::unique_function over to use these new, much
more portable traits. =D

Hopefully this will fix the build bot breakage from my prior commit.

llvm-svn: 336161
2018-07-03 01:18:21 +00:00
Teresa Johnson
91ec4ddcd7 [ThinLTO] Fix printing of aliases for distributed backend indexes
Summary:
When we import an alias (which will import a copy of the aliasee), but
aren't going to import the aliasee directly, the distributed backend
index will not contain the aliasee summary. Handle this in the summary
assembly printer by printing "null" as the aliasee.

Reviewers: davidxl, dexonsmith

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, llvm-commits

Differential Revision: https://reviews.llvm.org/D48699

llvm-svn: 336160
2018-07-03 01:11:43 +00:00
Erik Pilkington
b64d68c851 Some buildbots were choking on std::max_align_t, try using the global alias.
llvm-svn: 336159
2018-07-03 00:48:27 +00:00
Erik Pilkington
96a2826f94 [demangler] Fix a MSVC alignment warning.
This should fix llvm.org/PR37944

llvm-svn: 336157
2018-07-03 00:23:18 +00:00
Chandler Carruth
8159ba335a [ADT] Add llvm::unique_function which is like std::function but
supporting move-only closures.

Most of the core optimizations for std::function are here plus
a potentially novel one that detects trivially movable and destroyable
functors and implements those with fewer indirections.

This is especially useful as we start trying to add concurrency
primitives as those often end up with move-only types (futures,
promises, etc) and wanting them to work through lambdas.

As further work, we could add better support for things like const-qualified
operator()s to support more algorithms, and r-value ref qualified operator()s
to model call-once. None of that is here though.

We can also provide our own llvm::function that has some of the optimizations
used in this class, but with copy semantics instead of move semantics.

This is motivated by increasing usage of things like executors and the task
queue where it is useful to embed move-only types like a std::promise within
a type erased function. That isn't possible without this version of a type
erased function.

Differential Revision: https://reviews.llvm.org/D48349

llvm-svn: 336156
2018-07-02 23:57:29 +00:00
Teresa Johnson
de152c8016 Remove absolute path in test
My test change in r336148 accidentally included an absolute path, clean
that up to fix bot failures.

llvm-svn: 336151
2018-07-02 23:02:07 +00:00
Lang Hames
8b63c11e19 [ORC] Verify modules when running LLLazyJIT in LLI, and deal with fallout.
The verifier identified several modules that were broken due to incorrect
linkage on declarations. To fix this, CompileOnDemandLayer2::extractFunction
has been updated to change decls to external linkage.

llvm-svn: 336150
2018-07-02 22:30:18 +00:00
Teresa Johnson
cacd7a240a [ThinLTO] Fix printing of module paths for distributed backend indexes
Summary:
In the individual index files emitted for distributed ThinLTO backends,
the module path ids are not contiguous. Assign slots to module paths in
order to handle this better and also to get contiguous numbering in the
summary assembly.

Reviewers: davidxl, dexonsmith

Subscribers: mehdi_amini, inglorion, eraman, llvm-commits, steven_wu

Differential Revision: https://reviews.llvm.org/D48698

llvm-svn: 336148
2018-07-02 22:09:23 +00:00
Heejin Ahn
e0c76f2551 [WebAssembly] Support for atomic stores
Summary: Add support for atomic store instructions.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D48839

llvm-svn: 336145
2018-07-02 21:22:59 +00:00
Vadzim Dambrouski
2c8cd025cf [ARM] Fix PR37382: Don't optimize mul.with.overflow on thumbv6m.
Reviewers: efriedma, rogfer01, javed.absar

Reviewed By: efriedma, rogfer01

Subscribers: kristof.beyls, chrib, llvm-commits

Differential Revision: https://reviews.llvm.org/D48846

llvm-svn: 336144
2018-07-02 21:05:26 +00:00
Andrea Di Biagio
9758b05b3b [llvm-mca] Clear the content of map VariantDescriptors in InstrBuilder before we start analyzing a new CodeBlock. NFCI.
Different CodeBlocks don't overlap. The same MCInst cannot appear in more than
one code block because all blocks are instantiated before the simulation is run.

We should always clear the content of map VariantDescriptors before every
simulation, since VariantDescriptors cannot possibly store useful information
for the next blocks. It is also "safer" to clear its content because `MCInst*`
is used as the key type for map VariantDescriptors.

llvm-svn: 336142
2018-07-02 20:39:57 +00:00
Tim Shen
379ae77a60 [SCEV] Strengthen StrengthenNoWrapFlags (reapply r334428).
Summary:
Comment on Transforms/LoopVersioning/incorrect-phi.ll: With the change
SCEV is able to prove that the loop doesn't wrap-self (due to zext i16
to i64), disabling the entire loop versioning pass. Removed the zext and
just use i64.

Reviewers: sanjoy

Subscribers: jlebar, hiraditya, javed.absar, bixia, llvm-commits

Differential Revision: https://reviews.llvm.org/D48409

llvm-svn: 336140
2018-07-02 20:01:54 +00:00
Dan Gohman
8b8fb7355f [WebAssembly] Fix fast-isel optimization of branch conditions.
LLVM doesn't guarantee anything about the high bits of a register holding
an i1 value at the IR level, so don't translate LLVM IR i1 values directly
into WebAssembly conditional branch operands. WebAssembly's conditional
branches do demand all 32 bits be valid.

Fixes PR38019.

llvm-svn: 336138
2018-07-02 19:45:57 +00:00
Krzysztof Parzyszek
2a0fcfa9bf [X86] Add phony registers for high halves of regs with low halves
Add registers still missing after r328016 (D43353):
- for bits 15-8  of SI, DI, BP, SP (*H), and R8-R15 (*BH),
- for bits 31-16 of R8-R15 (*WH).

Thanks to Craig Topper for pointing it out.

llvm-svn: 336134
2018-07-02 19:05:09 +00:00
Alina Sbirlea
00ebfcda42 Replace "Replacable" with "Replaceable". [NFC]
llvm-svn: 336133
2018-07-02 18:53:40 +00:00
Fangrui Song
d9ba18363e Replace unused output filenames with /dev/null in tests
Similar to rLLD336129

llvm-svn: 336131
2018-07-02 18:16:44 +00:00
Farhana Aleen
d3e3e16e60 [SLP] Recognize min/max pattern using instructions producing same values.
Summary: It is common to have the following min/max pattern during the intermediate stages of SLP since we only optimize at the end. This patch tries to catch such patterns and allow more vectorization.

         %1 = extractelement <2 x i32> %a, i32 0
         %2 = extractelement <2 x i32> %a, i32 1
         %cond = icmp sgt i32 %1, %2
         %3 = extractelement <2 x i32> %a, i32 0
         %4 = extractelement <2 x i32> %a, i32 1
         %select = select i1 %cond, i32 %3, i32 %4

Author: FarhanaAleen

Reviewed By: ABataev, RKSimon, spatel

Differential Revision: https://reviews.llvm.org/D47608

llvm-svn: 336130
2018-07-02 17:55:31 +00:00
Sanjay Patel
a9bbbc0114 [InstCombine] reverse canonicalization of add --> or to allow more shuffle folding
This extends D48485 to allow another pair of binops (add/or) to be combined either
with or without a leading shuffle:
or X, C --> add X, C (when X and C have no common bits set)

Here, we need value tracking to determine that the 'or' can be reversed into an 'add',
and we've added general infrastructure to allow extending to other opcodes or moving 
to where other passes could use that functionality.

Differential Revision: https://reviews.llvm.org/D48662

llvm-svn: 336128
2018-07-02 17:42:29 +00:00
Francis Visoiu Mistrih
bb4cf24f14 [MC] Error on a .zerofill directive in a non-virtual section
On darwin, all virtual sections have zerofill type, and having a
.zerofill directive in a non-virtual section is not allowed. Instead of
asserting, show a nicer error.

In order to use the equivalent of .zerofill in a non-virtual section,
the usage of .zero of .space is required.

This patch replaces the assert with an error.

Differential Revision: https://reviews.llvm.org/D48517

llvm-svn: 336127
2018-07-02 17:29:43 +00:00
Dave Lee
1320ae98e2 nm: Add -no-weak flag for hiding weak symbols
Summary:
This adds a new -no-weak flag to nm to hide weak symbols in its output.
This also adds a -W alias for this which is analogous to -U.

Patch by Keith Smiley

Reviewers: kastiglione, enderby, compnerd

Reviewed By: kastiglione

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D48751

llvm-svn: 336126
2018-07-02 17:24:37 +00:00
Simon Pilgrim
e88119cb37 [SLPVectorizer][X86] Begin adding alternate tests for call operators
Alternate opcode handling only supports binary operators, these tests demonstrate a missed opportunity to vectorize ceil/floor calls

llvm-svn: 336125
2018-07-02 17:23:45 +00:00
Vedant Kumar
92c2c28ada Tighten up a test for -check-debugify, NFC
Use an -implicit-check-not to make sure an error which should not occur
in fact does not occur before the first CHECK line.

Suggested by Paul Robinson in post-commit feedback for r335897.

llvm-svn: 336123
2018-07-02 17:08:36 +00:00