Commit Graph

3711 Commits

Author SHA1 Message Date
Tobias Grosser b94863001a [ScopInfo] Do not use the set dimension ids to carry loop information
isl does not guarantee that set dimension ids will be preserved, so using them
to carry information is not a good idea. Furthermore, the loop information can
be derived without problem from the statement itself. As this even requires
less code than propagating loop information on set dimension ids, starting from
this commit we just derive the loop information in collectSurroundingLoops
directly from the IR.

Interestingly this also results in a couple of isl sets to take a simpler
representation.

llvm-svn: 326664
2018-03-03 19:27:54 +00:00
Philip Pfaffe 4d50ab86e6 Revert "[Acc] Fix for PR33208"
This reverts commit r326643. Fix didn't really fix anything.

llvm-svn: 326656
2018-03-03 15:34:49 +00:00
Philip Pfaffe a8f7cc8ec9 [Acc] Fix for PR33208
During codegen, Polly attempts to clear all loops from ScalarEvolution
and LoopInfo, and it does so one block at a time. This causes undefined
behaviour, since this way a loop header might be removed from a loop
before the entire loop is erased, causing ScalarEvolution to run into an
error.

Instead, just delete the entire loop atomically. This fixes currently
failing testcases.

llvm-svn: 326643
2018-03-03 10:47:37 +00:00
Tobias Grosser de6b342e90 isl: "isl_schedule_get_map: handle trees with divergent filter node parameters"
Also un-revert (isl_pw_*_alloc: add missing check for compatible spaces, Wed Sep
6 12:18:04 2017 +0200).

This patch is a proposed fix to avoid asserts due to stricter space checking
within isl, which resulted in failures when converting a schedule tree to
a schedule map.

llvm-svn: 326073
2018-02-26 09:26:41 +00:00
Tobias Grosser 718d04c653 Use isl::manage_copy to simplify calls to isl::manage(isl_.._copy())
As part of this cleanup a couple of unnecessary isl::manage(obj.copy()) pattern
are eliminated as well.

We checked for all potential cleanups by scanning for:

  "grep -R isl::manage\( lib/ | grep copy"

llvm-svn: 325558
2018-02-20 07:26:58 +00:00
Tobias Grosser fa8079d0dc Update isl to isl-0.18-1047-g4a20ef8
This update:

  - Removes several deprecated functions (e.g., isl_band).
  - Improves the pretty-printing of sets by detecting modulos and "false"
    equalities.
  - Minor improvements to coalescing and increased robustness of the isl
    scheduler.

This update does not yet include isl commit isl-0.18-90-gd00cb45
(isl_pw_*_alloc: add missing check for compatible spaces, Wed Sep 6 12:18:04
2017 +0200), as this additional check is too tight and unfortunately causes
two test case failures in Polly. A patch has been submitted to isl and will be
included in the next isl update for Polly.

llvm-svn: 325557
2018-02-20 07:26:42 +00:00
Tobias Grosser 85476dc45a Fix broken isl-noexceptions.h path in update-isl script
llvm-svn: 325556
2018-02-20 07:24:58 +00:00
Tobias Grosser ba4257b187 Update isl C++ bindings to latest version of isl
llvm-svn: 325555
2018-02-20 07:24:55 +00:00
Tobias Grosser 5f62fafadd Do not call band_list().dump()
This is in preparation for the removal of band_list from isl.

llvm-svn: 325554
2018-02-20 07:24:40 +00:00
Michael Kruse a6716d9d81 [ScopBuilder] scalar-indep: Fix mutually referencing PHIs.
Two or more PHIs mutually using each other directly or indirectly as
incoming value could cause that a PHI WRITE be added before the PHI READ
(i.e. it overwrites the current incoming value with the next incoming
value before it being read).

Fix by ensuring that the PHI WRITE and PHI READ are in the same statement.

This should fix the miscompile of SingleSource/Benchmark/Misc/whetstone
from the test-suite.

llvm-svn: 324934
2018-02-12 21:09:40 +00:00
Michael Kruse a43ba2d84f [ScopBuilder] Make -polly-stmt-granularity=scalar-indep the default.
Splitting basic blocks into multiple statements if there are now
additional scalar dependencies gives more freedom to the scheduler, but
more statements also means higher compile-time complexity. Switch to
finer statement granularity, the additional compile time should be
limited by the number of operations quota.

The regression tests are written for the -polly-stmt-granularity=bb
setting, therefore we add that flag to those tests that break with the
new default. Some of the tests only fail because the statements are
named differently due to a basic block resulting in multiple statements,
but which are removed during simplification of statements without
side-effects. Previous commits tried to reduce this effect, but it is
not completely avoidable.

Differential Revision: https://reviews.llvm.org/D42151

llvm-svn: 324169
2018-02-03 06:59:47 +00:00
Michael Kruse 217704f7a8 [ScopInfo] Allow epilogues to be the main statement of a BB.
Do not add a "_last" suffix to the statement name if there is no (other)
main statement for a basic block. In other words, it becomes the main
statement itself. This further reduces the statement naming difference
between -polly-stmt-granularity=bb and
-polly-stmt-granularity=scalar-indep.

llvm-svn: 324168
2018-02-03 05:43:00 +00:00
Michael Kruse 1a745a4ef6 Run clang-format after r324003. NFC.
llvm-svn: 324112
2018-02-02 18:11:58 +00:00
Benjamin Kramer e65c7bbe8a Update polly for r323999.
llvm-svn: 324003
2018-02-01 20:49:53 +00:00
Daniel Neilson 77a98366ce Change memcpy/memove/memset to have dest and source alignment attributes.
Summary:
  This change is step four in the series of changes to remove alignment argument from
memcpy/memmove/memset in favour of alignment attributes. Steps:

Step 1) Remove alignment parameter and create alignment parameter attributes for
memcpy/memmove/memset. ( rL322965, rC322964, rL322963 )
Step 2) Expand the IRBuilder API to allow creation of memcpy/memmove with differing
source and dest alignments. ( rL323597 )
Step 3) Update Clang to use the new IRBuilder API. ( rC323617 )
Step 4) Update Polly to use the new IRBuilder API.
Step 5) Update LLVM passes that create memcpy/memmove calls to use the new IRBuilder API,
and those that use use MemIntrinsicInst::[get|set]Alignment() to use [get|set]DestAlignment()
and [get|set]SourceAlignment() instead.
Step 6) Remove the single-alignment IRBuilder API for memcpy/memmove, and the
MemIntrinsicInst::[get|set]Alignment() methods.

Reference
   http://lists.llvm.org/pipermail/llvm-dev/2015-August/089384.html
   http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20151109/312083.html

Reviewers: jdoerfert, grosser, bollu

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41677

llvm-svn: 323618
2018-01-28 18:13:57 +00:00
Michael Kruse a230f22f4b [ScopBuilder] Prefer PHI Write accesses in the statement the incoming value is defined.
Theoretically, a PHI write can be added to any statement that represents
the incoming basic block. We previously always chose the last because
the incoming value's definition is guaranteed to be defined.

With this patch the PHI write is added to the statement that defines the
incoming value. It avoids the requirement for a scalar dependency between
the defining statement and the statement containing the write. As such the
logic for -polly-stmt-granularity=scalar-indep that ensures that there is
such scalar dependencies can be removed.

Differential Revision: https://reviews.llvm.org/D42147

llvm-svn: 323284
2018-01-23 23:56:36 +00:00
Michael Kruse 1ed2bc5266 [VirtualInst] Derive correct use kind of PHI operands. NFC.
VirtualUse::create is only called for MemoryKind::Value, but its
consistency nonetheless checked in verifyUses(). PHI uses are always
inter-stmt dependencies, which was not considered by the constructor
method. The virtual and non-virtual execution paths were the same, such
that verifyUses did not encounter any inconsistencies.

llvm-svn: 323283
2018-01-23 23:56:25 +00:00
Dimitry Andric e6de5a100d Assume the shared library path variable is LD_LIBRARY_PATH on systems
except Darwin and Windows.  This prevents inserting an environment
variable with an empty name (which is illegal and leads to a Python
exception) on any of the BSDs.

llvm-svn: 323041
2018-01-20 14:35:05 +00:00
Daniel Neilson 751a2cebc5 Change memcpy/memove/memset to have dest and source alignment attributes (Step 1).
Summary:
 Upstream LLVM is changing the the prototypes of the @llvm.memcpy/memmove/memset
intrinsics. This change updates the polly tests for this change.

 The @llvm.memcpy/memmove/memset intrinsics currently have an explicit argument
which is required to be a constant integer. It represents the alignment of the
dest (and source), and so must be the minimum of the actual alignment of the
two.

 This change removes the alignment argument in favour of placing the alignment
attribute on the source and destination pointers of the memory intrinsic call.

 For example, code which used to read:
  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dest, i8* %src, i32 100, i32 4, i1 false)
will now read
  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %dest, i8* align 4 %src, i32 100, i1 false)

 At this time the source and destination alignments must be the same (Step 1).
Step 2 of the change, to be landed shortly, will relax that contraint and allow
the source and destination to have different alignments.

llvm-svn: 322963
2018-01-19 17:12:48 +00:00
Michael Kruse 9cfb0ac223 [ScopBuilder] Revise statement naming when there are multiple statements per BB.
The goal is to have -polly-stmt-granularity=bb and
-polly-stmt-granularity=scalar-indep to have the same names if there is
just one statement per basic block.

This fixes a fluke when Polybench's jacobi-2d is optimized differently
depending on the -polly-stmt-granularity option, although both options
create the same SCoP, just with different statement names.

The new naming scheme is:

With -polly-use-llvm-names=0:
Stmt<BBIdx as decimal><Idx within BB as letter>

With -polly-use-llvm-names=1:
Stmt_BBName_<Idx within BB as letter>

The <Idx within BB> suffix is omitted for the main statement of a BB. The
main statement is either the one containing the first store or call
(those cannot be removed by the simplifyer), or if there is no such
instruction, the first. If after simplification there is just a single
statement left, it should be the main statement and have the same names as
with -polly-stmt-granularity=bb.

Differential Revision: https://reviews.llvm.org/D42136

llvm-svn: 322852
2018-01-18 15:15:50 +00:00
Michael Kruse d6e2208671 [ScopInfo] Pass name to ScopStmt ctor. NFC.
This will give control of the statement's name to the caller.
Required to give -polly-stmt-granularity=scalar-indep more control
over the name of the generated statement in a follow-up commit.

llvm-svn: 322851
2018-01-18 15:15:38 +00:00
Eli Friedman a75d53c83f [polly] [ScopInfo] Don't use isl_val_get_num_si.
isl_val_get_num_si crashes on overflow, so don't use it on arbitrary
integers.

Testcase only crashes on platforms where long is 32 bits because of the
signature of isl_val_get_num_si; not sure if it's possible to write a
testcase which crashes if long is 64 bits.

There are a few other places in polly which use isl_val_get_num_si;
they probably need to be fixed as well. I don't think polly uses any
of the other "long" isl APIs in an unsafe manner.

Differential Revision: https://reviews.llvm.org/D42129

llvm-svn: 322766
2018-01-17 21:59:02 +00:00
Michael Kruse a0db63a195 [IslTools] dumpPw: Dump same structure pieces together.
Print same or similar structure elements together. Previously, the
value could take more importance that the space structure if visited
first in the space nest tree.

Before:
{
  Left[0] -> Right[i]: i >= 0;
  Left[1] -> AnotherRight[i];
  Left[2] -> Right[-1]
}

After:
{
  Left[0] -> Right[i]: i >= 0;
  Left[2] -> Right[-1];
  Left[1] -> AnotherRight[i]
}

llvm-svn: 322581
2018-01-16 18:39:42 +00:00
Michael Kruse 21de8adc36 [CMake] Use only keyword-version of target_link_library. NFC.
CMake insists that for each target, one uses only the non-keyword
version of target_link_library

    target_link_library(mytarget lib)

or the one with PUBLIC/PRIVATE/INTERFACE keyword:

    target_link_library(mytarget PUBLIC lib)

Otherwise, CMake fails with the error message:

  The keyword signature for target_link_libraries has already been used with
  the target "mytarget".  All uses of target_link_libraries with a target
  must be either all-keyword or all-plain.

Change all occurances of target_link_library to the newer keyworded
version to avoid such errors. Some already have been changed in r319840,
but might not be sufficient for all build configurations to build
the doxygen manual.

Reported-by: Tanya Lattner <tanyalattner@llvm.org>
llvm-svn: 322376
2018-01-12 16:09:18 +00:00
Hans Wennborg e525b18620 Docs, release notes: update version to 7.0.0
llvm-svn: 321731
2018-01-03 15:54:54 +00:00
Michael Kruse 271deb17b0 [CodeGen] Fix noalias annotations for memcpy/memmove.
Memory transfer instructions take two pointers. It is not defined to
which of those a noalias annotation applies. To ensure correctness,
do not add noalias annotations to memcpy/memmove instructions anymore.

The caused a miscompile with test-suite's MultiSource/Applications/obsequi.
Since r321138, the MemCpyOpt pass would remove memcpy/memmove calls if
known to copy uninitialized memory. In that case, it was initialized
by another memcpy, but the annotation for the target pointer said
it would not alias. The annotation was actually meant for the source
pointer, which was was an alloca and could not alias with the target
pointer.

llvm-svn: 321371
2017-12-22 17:44:53 +00:00
Michael Kruse 5c2441901f Fix isl out-of-quota errors affecting later quota guards.
If an out-of-quota error occurred, the last error would be
isl_error_quota unless a different error occured. We typically check
whether the max-operations occured by comparing to that error value
after leaving the quota guard. This would check whether there ever
was a quota-error, not just in the last quota guards.

The observable bug occurred if the max-operations limit was reached in
DeLICM, and if -polly-dependences-computout=0, DependenceInfo would
think that the quota for computing dependencies was the reason,
i.e., fail the operation even if the calculation itself was successful.

Fix by reseting the last error to isl_error_none when entering a
quota guard, signaling that no quota error occured unless in the
guard's scope.

llvm-svn: 321329
2017-12-22 01:10:31 +00:00
Michael Kruse 5f0e8a46cf [ScopBuilder] Split statements on encountering store instructions.
Introduce -polly-stmt-granularity=store option.

Contributed-by: Nandini Singhal <cs15mtech01004@iith.ac.in>

Differential Revision: https://reviews.llvm.org/D37337

llvm-svn: 320360
2017-12-11 12:51:24 +00:00
Michael Kruse 188b437fcb [ScopBuilder] Fix typo. NFC.
Contributed-by: Nandini Singhal <cs15mtech01004@iith.ac.in>

Differential Revision: https://reviews.llvm.org/D41047

llvm-svn: 320336
2017-12-10 22:56:32 +00:00
Philip Pfaffe 0969462c52 [NFC] Fix formatting
llvm-svn: 319973
2017-12-06 22:01:08 +00:00
Philip Pfaffe d98dbeeb71 Port SCEVAffinator to the isl c++ bindings
Summary: Straight forward port of SCEVAffinator

Reviewers: grosser, bollu, Meinersbur

Reviewed By: Meinersbur

Subscribers: pollydev, llvm-commits

Differential Revision: https://reviews.llvm.org/D40803

llvm-svn: 319958
2017-12-06 21:02:22 +00:00
Shoaib Meenai d806af3499 [CMake] Use PRIVATE in target_link_libraries for executables
We currently use target_link_libraries without an explicit scope
specifier (INTERFACE, PRIVATE or PUBLIC) when linking executables.
Dependencies added in this way apply to both the target and its
dependencies, i.e. they become part of the executable's link interface
and are transitive.

Transitive dependencies generally don't make sense for executables,
since you wouldn't normally be linking against an executable. This also
causes issues for generating install export files when using
LLVM_DISTRIBUTION_COMPONENTS. For example, clang has a lot of LLVM
library dependencies, which are currently added as interface
dependencies. If clang is in the distribution components but the LLVM
libraries it depends on aren't (which is a perfectly legitimate use case
if the LLVM libraries are being built static and there are therefore no
run-time dependencies on them), CMake will complain about the LLVM
libraries not being in export set when attempting to generate the
install export file for clang. This is reasonable behavior on CMake's
part, and the right thing is for LLVM's build system to explicitly use
PRIVATE dependencies for executables.

Unfortunately, CMake doesn't allow you to mix and match the keyword and
non-keyword target_link_libraries signatures for a single target; i.e.,
if a single call to target_link_libraries for a particular target uses
one of the INTERFACE, PRIVATE, or PUBLIC keywords, all other calls must
also be updated to use those keywords. This means we must do this change
in a single shot. I also fully expect to have missed some instances; I
tested by enabling all the projects in the monorepo (except dragonegg),
and configuring both with and without shared libraries, on both Darwin
and Linux, but I'm planning to rely on the buildbots for other
configurations (since it should be pretty easy to fix those).

Even after this change, we still have a lot of target_link_libraries
calls that don't specify a scope keyword, mostly for shared libraries.
I'm thinking about addressing those in a follow-up, but that's a
separate change IMO.

Differential Revision: https://reviews.llvm.org/D40823

llvm-svn: 319840
2017-12-05 21:49:56 +00:00
Siddharth Bhat c0f5f4deae Update to latest clang-format. [NFC]
Differential Revision: https://reviews.llvm.org/D40791

llvm-svn: 319718
2017-12-05 00:06:09 +00:00
Philip Pfaffe f6f8b25e58 [NFC] In GPGPU testcases, replace numeric registers in CHECK directives.
Using numeric registers is flaky, since as soon as one additional
instruction is generated by us, all the tests need to be adapted.

llvm-svn: 319544
2017-12-01 14:16:39 +00:00
Philip Pfaffe 4fe21814d1 Handle Top-Level-Regions in polly::isHoistableLoad
Summary:
This can be seen as a follow-up on my previous differential [D33411](https://reviews.llvm.org/D33411).
We received a bug report where this error was triggered. I have tried my best to recreate the issue in a minimal lit testcase which is also part of this differential.

I only handle return instructions as predecessors to a virtual TLR-exit right now. From inspecting the codebase, it seems `unreachable` instructions may also be of interest here. If requested, I can extend my patches to consider them as well. I would also apply this on `ScopHelper.cpp::isErrorBlock` (see D33411), of course.

Reviewers: philip.pfaffe, bollu

Reviewed By: bollu

Subscribers: Meinersbur, pollydev, llvm-commits

Tags: #polly

Differential Revision: https://reviews.llvm.org/D40492

llvm-svn: 319431
2017-11-30 13:06:10 +00:00
Michael Kruse bfb8fa5a16 Update format after clang-format change. NFC.
In r319314 clang-format changed its reflowing logic.

llvm-svn: 319426
2017-11-30 12:05:48 +00:00
Ben Hamilton 85db2bf7b6 [polly] Set up .arcconfig to point to new Diffusion PLO repository
Summary: We want to automatically copy the appropriate mailing list
for review requests to the polly repository.

For context, see the proposal and discussion here:

http://lists.llvm.org/pipermail/cfe-dev/2017-November/056032.html

Similar to D40179, I set up a new Diffusion repository with callsign
"PLO" for polly:

https://reviews.llvm.org/source/polly/

This explicitly updates polly's .arcconfig to point to the new C
repository in Diffusion, which will let us use Herald rule H270.

llvm-svn: 319056
2017-11-27 17:34:03 +00:00
Davide Italiano b0c7dee0b6 [MaximalStaticExpansion] Simplify this code a bit. NFCI.
llvm-svn: 318988
2017-11-25 23:01:31 +00:00
Michael Kruse 163cacb469 [CodeGen] Detect empty domain because of parameters context.
Isl does not allow generating isl_ast_expr from an isl_pw_aff that has an
empty domain (i.e. has no pieces). We already detected the case if the
isl_pw_aff comes with an empty domain.

isl_ast_build also considers the domain empty if it is disjoint with the
parameter context (e.g. parameters values that we exclude by runtime
versioning).

Intersect the access relation domain with the parameter context to
also detect such practically empty access domains. The effective
pointer used in the generated code is unimportand because it will never
be executed.

This fixes llvm.org/PR35362

llvm-svn: 318806
2017-11-21 22:11:10 +00:00
Michael Kruse 58166b13e0 Run polly-update-format. NFC.
polly-check-format has been failing since at least r318517,
due to more than one cause.

llvm-svn: 318795
2017-11-21 19:25:26 +00:00
Philip Pfaffe 00fd43b327 Port ScopInfo to the isl cpp bindings
Summary:
Most changes are mechanical, but in one place I changed the program semantics
by fixing a likely bug:

In `Scop::hasFeasibleRuntimeContext()`, I'm now explicitely handling the
error-case. Before, when the call to `addNonEmptyDomainConstraints()`
returned a null set, this (probably) accidentally worked because
isl_bool_error converts to true. I'm checking for nullptr now.

Reviewers: grosser, Meinersbur, bollu

Reviewed By: Meinersbur

Subscribers: nemanjai, kbarton, pollydev, llvm-commits

Differential Revision: https://reviews.llvm.org/D39971

llvm-svn: 318632
2017-11-19 22:13:34 +00:00
Zhaoshi Zheng ceec175dff [NFC] Make r318597 compatible with clang-format
llvm-svn: 318561
2017-11-17 22:05:19 +00:00
Philip Pfaffe 2813ce228b [nfc] Iwyu: forward-declare/include raw_ostream in zone algo
llvm-svn: 318517
2017-11-17 11:34:29 +00:00
Philip Pfaffe 8dd0f479e8 [SI] Fix a potential use-after-free
Summary:
There is a potential use-after-free bug in Scop::buildSchedule(Region *,
LoopStackTy &, LoopInfo &).  Before, we took a reference to LoopStack.back()
which is a use after free, since back is popped off further below. This didn't
crash before by pure chance, since LoopStack is actually a vector, and the
memory isn't freed upon pop. I turned this into an iterator-based algorithm.

Reviewers: grosser, bollu, Meinersbur

Reviewed By: Meinersbur

Subscribers: llvm-commits, pollydev

Differential Revision: https://reviews.llvm.org/D39979

llvm-svn: 318415
2017-11-16 16:35:19 +00:00
Mandeep Singh Grang 02e789c9bf [polly] Remove redundant return [NFC]
Reviewers: grosser, bollu

Reviewed By: grosser

Subscribers: nemanjai, kbarton, llvm-commits

Tags: #polly

Differential Revision: https://reviews.llvm.org/D39916

llvm-svn: 317922
2017-11-10 20:33:08 +00:00
Michael Kruse 3a1e4bfb53 Update formatting to reflect change in clang-format. NFC.
clang-format has changed its algorithm
for sorting includes in r317794.

llvm-svn: 317808
2017-11-09 16:33:29 +00:00
Michael Kruse 4d3f3c7206 [ForwardOpTree] Limit isl operations of known content reload.
Put the analysis part of reloadKnownContent under an isl
max-operations quota scope, as has already been done for
forwardKnownLoad.

This should fix the aosp timeout of "GrTestUtils.cpp".

llvm-svn: 317495
2017-11-06 17:48:14 +00:00
Sanjay Patel 1b5114fa52 [Analysis] update to use new fast-math API - isFast()
llvm-svn: 317491
2017-11-06 16:52:31 +00:00
Florian Hahn 6720a089fd [Polly] Fix using order, as this caused a test failure (NFC)
Summary:
Without this patch, clang-format in check-polly fails for me, with current master:

```
FAILED: cd build/tools/polly && build/bin/clang-format -sort-includes -style=llvm llvm/tools/polly/include/polly/ScopPass.h | diff -u llvm/tools/polly/include/polly/ScopPass.h -
--- llvm/tools/polly/include/polly/ScopPass.h	2017-11-06 14:05:49.885345000 +0000
+++ -	2017-11-06 14:07:24.956241758 +0000
@@ -40,12 +40,12 @@
 } // namespace polly

 namespace llvm {
+using polly::SPMUpdater;
 using polly::Scop;
 using polly::ScopAnalysisManager;
 using polly::ScopAnalysisManagerFunctionProxy;
 using polly::ScopInfo;
 using polly::ScopStandardAnalysisResults;
-using polly::SPMUpdater;

 template <>
 class InnerAnalysisManagerProxy<ScopAnalysisManager, Function>::Result {
```

Reviewers: grosser, Meinersbur, bollu

Reviewed By: Meinersbur

Subscribers: llvm-commits, pollydev

Differential Revision: https://reviews.llvm.org/D39683

llvm-svn: 317478
2017-11-06 14:26:04 +00:00
Michael Kruse 68821a8b91 [ZoneAlgo/ForwardOpTree] Normalize PHIs to their known incoming values.
Represent PHIs by their incoming values instead of an opaque value of
themselves. This allows ForwardOpTree to "look through" the PHIs and
forward the incoming values since forwardings PHIs is currently not
supported.

This is particularly useful to cope with PHIs inserted by GVN LoadPRE.
The incoming values all resolve to a load from a single array element
which then can be forwarded.

It should in theory also reduce spurious conflicts in value mapping
(DeLICM), but I have not yet found a profitable case yet, so it is
not included here.

To avoid transitive closure and potentially necessary overapproximations
of those, PHIs that may reference themselves are excluded from
normalization and keep their opaque self-representation.

Differential Revision: https://reviews.llvm.org/D39333

llvm-svn: 317008
2017-10-31 16:11:46 +00:00