Commit Graph

426 Commits

Author SHA1 Message Date
Artem Dergachev 59428d182f [analyzer] Fix leak false positives on stuff put in C++/ObjC initializer lists.
The analyzer now realizes that C++ std::initializer_list objects and
Objective-C boxed structure/array/dictionary expressions can potentially
maintain a reference to the objects that were put into them. This avoids
false memory leak posivites and a few other issues.

This is a conservative behavior; for now, we do not model what actually happens
to the objects after being passed into such initializer lists.

rdar://problem/32918288
Differential Revision: https://reviews.llvm.org/D35216

llvm-svn: 314975
2017-10-05 08:43:32 +00:00
Peter Szecsi 0db84863d0 [StaticAnalyzer] LoopUnrolling: Keep track the maximum number of steps for each loop
This way the unrolling can be restricted for loops which will take at most a
given number of steps. It is defined as 128 in this patch and it seems to have
a good number for that purpose.

Differential Revision: https://reviews.llvm.org/D37181

llvm-svn: 311883
2017-08-28 10:50:28 +00:00
Peter Szecsi d91554bc91 [StaticAnalyzer] LoopUnrolling fixes
1. The LoopUnrolling feature needs the LoopExit included in the CFG so added this
dependency via the config options
2. The LoopExit element can be encountered even if we haven't encountered the 
block of the corresponding LoopStmt. So the asserts were not right.
3. If we are caching out the Node then we get a nullptr from generateNode which
case was not handled.


Differential Revision: https://reviews.llvm.org/D37103

llvm-svn: 311880
2017-08-28 10:21:24 +00:00
Peter Szecsi 3c3e1b0b54 [StaticAnalyzer] LoopUnrolling: Track a LoopStack in order to completely unroll specific loops
The LoopExit CFG information provides the opportunity to not mark the loops but
having a stack which tracks if a loop is unrolled or not. So in case of
simulating a loop we just add it and the information if it meets the
requirements to be unrolled to the top of the stack.

Differential Revision: https://reviews.llvm.org/D35684

llvm-svn: 311346
2017-08-21 16:32:57 +00:00
Peter Szecsi 4aa5e10fcc [StaticAnalyzer] Handle LoopExit CFGElement in the analyzer
This patch adds handling of the LoopExit CFGElements to the StaticAnalyzer.
This is reached by introducing a new ProgramPoint.
Tests will be added in a following commit.

Differential Revision: https://reviews.llvm.org/D35670

llvm-svn: 311344
2017-08-21 16:10:19 +00:00
Peter Szecsi 999a25ff72 [CFG] Add LoopExit information to CFG
This patch introduces a new CFG element CFGLoopExit that indicate when a loop
ends. It does not deal with returnStmts yet (left it as a TODO).
It hidden behind a new analyzer-config flag called cfg-loopexit (false by
default).
Test cases added.

The main purpose of this patch right know is to make loop unrolling and loop
widening easier and more efficient. However, this information can be useful for
future improvements in the StaticAnalyzer core too.

Differential Revision: https://reviews.llvm.org/D35668

llvm-svn: 311235
2017-08-19 11:19:16 +00:00
Peter Szecsi 8de103f2f0 [StaticAnalyzer] LoopUnrolling: Exclude cases where the counter is escaped before the loop
Adding escape check for the counter variable of the loop.
It is achieved by jumping back on the ExplodedGraph to its declStmt.

Differential Revision: https://reviews.llvm.org/D35657

llvm-svn: 311234
2017-08-19 10:24:52 +00:00
Peter Szecsi 657ac14816 [StaticAnalyzer] Completely unrolling specific loops with known bound option
This feature allows the analyzer to consider loops to completely unroll.
New requirements/rules (for unrolling) can be added easily via ASTMatchers.

Right now it is hidden behind a flag, the aim is to find the correct heuristic
and create a solution which results higher coverage % and more precise
analysis, thus can be enabled by default.

Right now the blocks which belong to an unrolled loop are marked by the
LoopVisitor which adds them to the ProgramState.
Then whenever we encounter a CFGBlock in the processCFGBlockEntrance which is
marked then we skip its investigating. That means, it won't be considered to
be visited more than the maximal bound for visiting since it won't be checked.

llvm-svn: 309006
2017-07-25 19:23:23 +00:00
Peter Szecsi 58a8b6b4af Revert "[StaticAnalyzer] Completely unrolling specific loops with known bound option"
Revert r308561 and r308558.

Clang-ppc64be-linux seems to crash while running the test cases.

llvm-svn: 308592
2017-07-20 07:35:11 +00:00
Peter Szecsi cb387b11df This feature allows the analyzer to consider loops to completely unroll. New
requirements/rules (for unrolling) can be added easily via ASTMatchers.

The current implementation is hidden behind a flag.

Right now the blocks which belong to an unrolled loop are marked by the 
LoopVisitor which adds them to the ProgramState. Then whenever we encounter a
CFGBlock in the processCFGBlockEntrance which is marked then we skip its
investigating. That means, it won't be considered to be visited more than the
maximal bound for visiting since it won't be checked.

Differential Revision: https://reviews.llvm.org/D34260

llvm-svn: 308558
2017-07-19 23:50:00 +00:00
Matthias Gehre 351c218d15 CFG: Add CFGElement for automatic variables that leave the scope
Summary:
This mimics the implementation for the implicit destructors. The
generation of this scope leaving elements is hidden behind
a flag to the CFGBuilder, thus it should not affect existing code.

Currently, I'm missing a test (it's implicitly tested by the clang-tidy
lifetime checker that I'm proposing).
I though about a test using debug.DumpCFG, but then I would
have to add an option to StaticAnalyzer/Core/AnalyzerOptions
to enable the scope leaving CFGElement,
which would only be useful to that particular test.

Any other ideas how I could make a test for this feature?

Reviewers: krememek, jordan_rose

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D15031

llvm-svn: 307759
2017-07-12 07:04:19 +00:00
Galina Kistanova a65d5785d8 Added LLVM_FALLTHROUGH to address warning: this statement may fall through. NFC.
llvm-svn: 304644
2017-06-03 06:26:27 +00:00
Alexander Shaposhnikov 015da3534a [analyzer] Fix assert in ExprEngine::processSwitch
This diff replaces getTypeSize(CondE->getType())) 
with getIntWidth(CondE->getType())) in ExprEngine::processSwitch.
These calls are not equivalent for bool, see ASTContext.cpp
Add a test case.

Test plan:
make check-clang-analysis
make check-clang

Differential revision: https://reviews.llvm.org/D32328

llvm-svn: 300936
2017-04-21 01:05:26 +00:00
Artem Dergachev 647804a84a [analyzer] When creating a temporary object, properly copy the value into it.
Adjustments should be considered properly; we should copy the unadjusted object
over the whole temporary base region. If the unadjusted object is no longer
available in the Environment, invalidate the temporary base region, and then
copy the adjusted object into the adjusted sub-region of the temporary region.

This fixes a regression introduced by r288263, that caused various
false positives, due to copying only adjusted object into the adjusted region;
the rest of the base region therefore remained undefined.
Before r288263, the adjusted value was copied over the unadjusted region,
which is incorrect, but accidentally worked better due to how region store
disregards compound value bindings to non-base regions.

An additional test machinery is introduced to make sure that despite making
two binds, we only notify checkers once for both of them, without exposing
the partially copied objects.

This fix is a hack over a hack. The proper fix would be to model C++ temporaries
in the CFG, and after that dealing with adjustments would no longer be
necessary, and the values we need would no longer disappear from the
Environment.

rdar://problem/30658168

Differential Revision: https://reviews.llvm.org/D30534

llvm-svn: 298924
2017-03-28 15:43:26 +00:00
Eric Fiselier 20f25cb6df [coroutines] Add DependentCoawaitExpr and fix re-building CoroutineBodyStmt.
Summary:
The changes contained in this patch are:

1. Defines a new AST node `CoawaitDependentExpr` for representing co_await expressions while the promise type is still dependent.
2. Correctly detect and transform the 'co_await' operand to  `p.await_transform(<expr>)`  when possible.
3. Change the initial/final suspend points to build during the initial parse, so they have the correct operator co_await lookup results.
4.  Fix transformation of the CoroutineBodyStmt so that it doesn't re-build the final/initial suspends.


@rsmith: This change is a little big, but it's not trivial for me to split it up. Please let me know if you would prefer this submitted as multiple patches.



Reviewers: rsmith, GorNishanov

Reviewed By: rsmith

Subscribers: ABataev, rsmith, mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D26057

llvm-svn: 297093
2017-03-06 23:38:15 +00:00
Aleksei Sidorin f82a63277a [Analyzer] Terminate analysis on OpenMP code instead of assertion crash
* ExprEngine assumes that OpenMP statements should never appear in CFG.
  However, current CFG doesn't know anything about OpenMP and passes
  such statements as CFG nodes causing "UNREACHABLE executed!" crashes.
  Since there is no OpenMP implementation in ExprEngine or CFG,
  we stop the analysis on OpenMP statements to avoid crashes.

This fixes PR31835.

Differential Revision: https://reviews.llvm.org/D30565

llvm-svn: 296884
2017-03-03 16:58:53 +00:00
Devin Coughlin bfa8e28dbb [analyzer] pr32088: Don't destroy the temporary if its initializer causes return.
In the following code involving GNU statement-expression extension:
  struct S {
    ~S();
  };

  void foo() {
    const S &x = ({ return; S(); });
  }
function 'foo()' returns before reference x is initialized. We shouldn't call
the destructor for the temporary object lifetime-extended by 'x' in this case,
because the object never gets constructed in the first place.

The real problem is probably in the CFG somewhere, so this is a quick-and-dirty
hotfix rather than the perfect solution.

A patch by Artem Dergachev!

rdar://problem/30759076

Differential Revision: https://reviews.llvm.org/D30499

llvm-svn: 296646
2017-03-01 17:48:39 +00:00
Anna Zaks b570195c3a [analyzer] Add LocationContext as a parameter to checkRegionChanges
This patch adds LocationContext to checkRegionChanges and removes
wantsRegionChangeUpdate as it was unused.

A patch by Krzysztof Wiśniewski!

Differential Revision: https://reviews.llvm.org/D27090

llvm-svn: 291869
2017-01-13 00:50:57 +00:00
Artem Dergachev 1d4fb84d82 [analyzer] Don't dereference the array value when binding it to a reference.
This replaces the hack in r291754, which was fixing pr31592, which was
caused by r291754, with a more appropriate solution.

rdar://problem/28832541
Differential revision: https://reviews.llvm.org/D28602

llvm-svn: 291781
2017-01-12 18:00:03 +00:00
Kelvin Li da68118729 [OpenMP] Sema and parsing for 'target teams distribute simd’ pragma
This patch is to implement sema and parsing for 'target teams distribute simd’ pragma.
    
Differential Revision: https://reviews.llvm.org/D28252

llvm-svn: 291579
2017-01-10 18:08:18 +00:00
Gabor Horvath 3d57457298 [analyzer] Add checker for iterators dereferenced beyond their range.
Patch by: Adam Balogh!

Differential Revision: https://reviews.llvm.org/D25660

llvm-svn: 291430
2017-01-09 09:52:32 +00:00
Kelvin Li 1851df563d [OpenMP] Sema and parsing for 'target teams distribute parallel for simd’ pragma
This patch is to implement sema and parsing for 'target teams distribute parallel for simd’ pragma.

Differential Revision: https://reviews.llvm.org/D28202

llvm-svn: 290862
2017-01-03 05:23:48 +00:00
Kelvin Li 80e8f56284 [OpenMP] Sema and parsing for 'target teams distribute parallel for’ pragma
This patch is to implement sema and parsing for 'target teams distribute parallel for’ pragma.

Differential Revision: https://reviews.llvm.org/D28160

llvm-svn: 290725
2016-12-29 22:16:30 +00:00
Kelvin Li 83c451e998 [OpenMP] Sema and parsing for 'target teams distribute' pragma
This patch is to implement sema and parsing for 'target teams distribute' pragma.

Differential Revision: https://reviews.llvm.org/D28015

llvm-svn: 290508
2016-12-25 04:52:54 +00:00
Kelvin Li bf594a5600 [OpenMP] Sema and parsing for 'target teams' pragma
This patch is to implement sema and parsing for 'target teams' pragma.

Differential Revision: https://reviews.llvm.org/D27818

llvm-svn: 290038
2016-12-17 05:48:59 +00:00
Richard Smith 30e304e2a6 Remove custom handling of array copies in lambda by-value array capture and
copy constructors of classes with array members, instead using
ArrayInitLoopExpr to represent the initialization loop.

This exposed a bug in the static analyzer where it was unable to differentiate
between zero-initialized and unknown array values, which has also been fixed
here.

llvm-svn: 289618
2016-12-14 00:03:17 +00:00
Richard Smith 410306bf6e Add two new AST nodes to represent initialization of an array in terms of
initialization of each array element:

 * ArrayInitLoopExpr is a prvalue of array type with two subexpressions:
   a common expression (an OpaqueValueExpr) that represents the up-front
   computation of the source of the initialization, and a subexpression
   representing a per-element initializer
 * ArrayInitIndexExpr is a prvalue of type size_t representing the current
   position in the loop

This will be used to replace the creation of explicit index variables in lambda
capture of arrays and copy/move construction of classes with array elements,
and also C++17 structured bindings of arrays by value (which inexplicably allow
copying an array by value, unlike all of C++'s other array declarations).

No uses of these nodes are introduced by this change, however.

llvm-svn: 289413
2016-12-12 02:53:20 +00:00
Kelvin Li 7ade93f5e2 [OpenMP] Sema and parsing for 'teams distribute parallel for' pragma
This patch is to implement sema and parsing for 'teams distribute parallel for' pragma.
    
Differential Revision: https://reviews.llvm.org/D27345

llvm-svn: 289179
2016-12-09 03:24:30 +00:00
Kelvin Li 579e41ced2 [OpenMP] Sema and parsing for 'teams distribute parallel for simd' pragma
This patch is to implement sema and parsing for 'teams distribute parallel for simd' pragma.

Differential Revision: https://reviews.llvm.org/D27084

llvm-svn: 288294
2016-11-30 23:51:03 +00:00
Artem Dergachev 28ee2d1b09 [analyzer] Construct temporary objects of correct types, destroy them properly.
When constructing a temporary object region, which represents the result of
MaterializeTemporaryExpr, track down the sub-expression for which the temporary
is necessary with a trick similar to the approach used in CodeGen, namely
by using Expr::skipRValueSubobjectAdjustments().

Then, create the temporary object region with type of that sub-expression.
That type would propagate further in a path-sensitive manner.

During destruction of lifetime-extened temporaries, consult the type of
the temporary object region, rather than the type of the lifetime-extending
variable, in order to call the correct destructor (fixes pr17001) and,
at least, not to crash by trying to call a destructor of a plain type
(fixes pr19539).

rdar://problem/29131302
rdar://problem/29131576

Differential Revision: https://reviews.llvm.org/D26839

llvm-svn: 288263
2016-11-30 19:02:44 +00:00
Anna Zaks 1485992eb3 [analyzer] Remove unused check::RegionChanges::wantsRegionChangeUpdate callback
Remove the check::RegionChanges::wantsRegionChangeUpdate callback as it is no
longer used (since checkPointerEscape has been added).

A patch by Krzysztof Wiśniewski!

Differential Revision: https://reviews.llvm.org/D26759

llvm-svn: 287175
2016-11-16 22:59:01 +00:00
Dominic Chen 3f8c3fa72f [analyzer] Rename assumeWithinInclusiveRange*()
Summary: The name is slightly confusing, since the constraint is not necessarily within the range unless `Assumption` is true. Split out renaming for ConstraintManager.h from D26061

Reviewers: zaks.anna, dcoughlin

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D26644

llvm-svn: 286927
2016-11-15 01:54:41 +00:00
Kelvin Li 4e325f77a9 Re-apply patch r279045.
llvm-svn: 285066
2016-10-25 12:50:55 +00:00
Daniel Marjamaki d99ebc03f4 [analyzer] Don't merge different return nodes in ExplodedGraph
Returns when calling an inline function should not be merged in the ExplodedGraph unless they are same.

Differential Revision: https://reviews.llvm.org/D25326

llvm-svn: 283554
2016-10-07 14:21:08 +00:00
Anna Zaks fb859a934a [analyzer] Add PostStmt callback for ArraySubscriptExpr
A patch by Jan Smets!

Differential Revision: https://reviews.llvm.org/D25009

llvm-svn: 283253
2016-10-04 20:49:31 +00:00
Alexander Shaposhnikov 6956d29034 [analyzer] Fix ExprEngine::VisitMemberExpr
AST may contain intermediate ParenExpr nodes
between MemberExpr and ArrayToPointerDecay.
This diff adjusts the check in ExprEngine::VisitMemberExpr accordingly.
Test plan: make -j8 check-clang-analysis

Differential revision: https://reviews.llvm.org/D24484

llvm-svn: 281373
2016-09-13 19:17:20 +00:00
Aleksei Sidorin 29afb1937b [analyzer] ExprEngine: remove second call to PreStmt<CastExpr>
This patch also introduces AnalysisOrderChecker which is intended for testing
of callback call correctness.

Differential Revision: https://reviews.llvm.org/D23804

llvm-svn: 280367
2016-09-01 13:55:38 +00:00
Diana Picus 8b44bbc077 Revert "[OpenMP] Sema and parsing for 'teams distribute simd’ pragma"
This reverts commit r279003 as it breaks some of our buildbots (e.g.
clang-cmake-aarch64-quick, clang-x86_64-linux-selfhost-modules).

The error is in OpenMP/teams_distribute_simd_ast_print.cpp:
clang: /home/buildslave/buildslave/clang-cmake-aarch64-quick/llvm/include/llvm/ADT/DenseMap.h:527:
bool llvm::DenseMapBase<DerivedT, KeyT, ValueT, KeyInfoT, BucketT>::LookupBucketFor(const LookupKeyT&, const BucketT*&) const
[with LookupKeyT = clang::Stmt*; DerivedT = llvm::DenseMap<clang::Stmt*, long unsigned int>;
      KeyT = clang::Stmt*; ValueT = long unsigned int;
      KeyInfoT = llvm::DenseMapInfo<clang::Stmt*>;
      BucketT = llvm::detail::DenseMapPair<clang::Stmt*, long unsigned int>]:
Assertion `!KeyInfoT::isEqual(Val, EmptyKey) && !KeyInfoT::isEqual(Val, TombstoneKey) &&
"Empty/Tombstone value shouldn't be inserted into map!"' failed.

llvm-svn: 279045
2016-08-18 09:25:07 +00:00
Kelvin Li 0e3bde8216 [OpenMP] Sema and parsing for 'teams distribute simd’ pragma
This patch is to implement sema and parsing for 'teams distribute simd’ pragma.

This patch is originated by Carlo Bertolli.

Differential Revision: https://reviews.llvm.org/D23528

llvm-svn: 279003
2016-08-17 23:13:03 +00:00
Kelvin Li 0253287633 [OpenMP] Sema and parsing for 'teams distribute' pragma
This patch is to implement sema and parsing for 'teams distribute' pragma.

Differential Revision: https://reviews.llvm.org/D23189

llvm-svn: 277818
2016-08-05 14:37:37 +00:00
Artem Dergachev 7929bf22fb [analyzer] Pring LocationContext in ExplodedGraph dumps.
Remove some FIXMEs in the surrounding code,
which have been addressed long time ago
by introducing checker-specific tags.

Differential Revision: https://reviews.llvm.org/D22622

llvm-svn: 276557
2016-07-24 08:15:58 +00:00
Kelvin Li 986330c190 [OpenMP] Sema and parsing for 'target simd' pragma
This patch is to implement sema and parsing for 'target simd' pragma.

Differential Revision: https://reviews.llvm.org/D22479

llvm-svn: 276203
2016-07-20 22:57:10 +00:00
Mehdi Amini 9670f847b8 [NFC] Header cleanup
Summary: Removed unused headers, replaced some headers with forward class declarations

Patch by: Eugene <claprix@yandex.ru>

Differential Revision: https://reviews.llvm.org/D20100

llvm-svn: 275882
2016-07-18 19:02:11 +00:00
Erik Pilkington 29099ded0c [ObjC] Implement @available in the Parser and AST
This patch adds a new AST node: ObjCAvailabilityCheckExpr, and teaches the
Parser and Sema to generate it. This node represents an availability check of
the form:

  @available(macos 10.10, *);

Which will eventually compile to a runtime check of the host's OS version. This
is the first patch of the feature I proposed here:
http://lists.llvm.org/pipermail/cfe-dev/2016-July/049851.html

Differential Revision: https://reviews.llvm.org/D22171

llvm-svn: 275654
2016-07-16 00:35:23 +00:00
Kelvin Li a579b9196c [OpenMP] Sema and parsing for 'target parallel for simd' pragma
This patch is to implement sema and parsing for 'target parallel for simd' pragma.

Differential Revision: http://reviews.llvm.org/D22096

llvm-svn: 275365
2016-07-14 02:54:56 +00:00
Devin Coughlin cad622742e [analyzer] Add rudimentary handling of AtomicExpr.
This proposed patch adds crude handling of atomics to the static analyzer.
Rather than ignore AtomicExprs, as we now do, this patch causes the analyzer
to escape the arguments. This is imprecise -- and we should model the
expressions fully in the future -- but it is less wrong than ignoring their
effects altogether.

This is rdar://problem/25353187

Differential Revision: http://reviews.llvm.org/D21667

llvm-svn: 274816
2016-07-08 00:53:18 +00:00
Kelvin Li 787f3fcc6b [OpenMP] Sema and parsing for 'distribute simd' pragma
Summary: This patch is an implementation of sema and parsing for the OpenMP composite pragma 'distribute simd'.

Differential Revision: http://reviews.llvm.org/D22007

llvm-svn: 274604
2016-07-06 04:45:38 +00:00
Kelvin Li 4a39add05e [OpenMP] Sema and parse for 'distribute parallel for simd'
Summary: This patch is an implementation of sema and parsing for the OpenMP composite pragma 'distribute parallel for simd'.

Differential Revision: http://reviews.llvm.org/D21977

llvm-svn: 274530
2016-07-05 05:00:15 +00:00
Richard Smith 5179eb7821 P0136R1, DR1573, DR1645, DR1715, DR1736, DR1903, DR1941, DR1959, DR1991:
Replace inheriting constructors implementation with new approach, voted into
C++ last year as a DR against C++11.

Instead of synthesizing a set of derived class constructors for each inherited
base class constructor, we make the constructors of the base class visible to
constructor lookup in the derived class, using the normal rules for
using-declarations.

For constructors, UsingShadowDecl now has a ConstructorUsingShadowDecl derived
class that tracks the requisite additional information. We create shadow
constructors (not found by name lookup) in the derived class to model the
actual initialization, and have a new expression node,
CXXInheritedCtorInitExpr, to model the initialization of a base class from such
a constructor. (This initialization is special because it performs real perfect
forwarding of arguments.)

In cases where argument forwarding is not possible (for inalloca calls,
variadic calls, and calls with callee parameter cleanup), the shadow inheriting
constructor is not emitted and instead we directly emit the initialization code
into the caller of the inherited constructor.

Note that this new model is not perfectly compatible with the old model in some
corner cases. In particular:
 * if B inherits a private constructor from A, and C uses that constructor to
   construct a B, then we previously required that A befriends B and B
   befriends C, but the new rules require A to befriend C directly, and
 * if a derived class has its own constructors (and so its implicit default
   constructor is suppressed), it may still inherit a default constructor from
   a base class

llvm-svn: 274049
2016-06-28 19:03:57 +00:00
Carlo Bertolli 9925f15661 Resubmission of http://reviews.llvm.org/D21564 after fixes.
[OpenMP] Initial implementation of parse and sema for composite pragma 'distribute parallel for'

This patch is an initial implementation for #distribute parallel for.
The main differences that affect other pragmas are:

The implementation of 'distribute parallel for' requires blocking of the associated loop, where blocks are "distributed" to different teams and iterations within each block are scheduled to parallel threads within each team. To implement blocking, sema creates two additional worksharing directive fields that are used to pass the team assigned block lower and upper bounds through the outlined function resulting from 'parallel'. In this way, scheduling for 'for' to threads can use those bounds.
As a consequence of blocking, the stride of 'distribute' is not 1 but it is equal to the blocking size. This is returned by the runtime and sema prepares a DistIncrExpr variable to hold that value.
As a consequence of blocking, the global upper bound (EnsureUpperBound) expression of the 'for' is not the original loop upper bound (e.g. in for(i = 0 ; i < N; i++) this is 'N') but it is the team-assigned block upper bound. Sema creates a new expression holding the calculation of the actual upper bound for 'for' as UB = min(UB, PrevUB), where UB is the loop upper bound, and PrevUB is the team-assigned block upper bound.

llvm-svn: 273884
2016-06-27 14:55:37 +00:00