Commit Graph

86 Commits

Author SHA1 Message Date
Arthur Eubanks 70dc3b811e [AggressiveInstCombine] Remove legacy PM pass
As part of legacy PM optimization pipeline removal.

This shouldn't be used in codegen pipelines so it should be ok to remove.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D137116
2022-11-15 14:35:15 -08:00
Sebastian Peryt 46fc75ab28 [NFC][2/n] Remove PrunePH pass
Second patch in the series to remove legacy PM and
associated -enable-new-pm=0 flag targets pass that
has not been ported to new PM - PruneEH.
Discussion about this can be found in D44415.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D134686
2022-09-26 18:38:04 -07:00
Nikita Popov 217e85761c [ArgPromotion] Remove legacy PM support
Support for the legacy pass manager in ArgPromotion causes
complications in D125485. As the legacy pass manager for middle-end
optimizations is unsupported, drop ArgPromotion from the legacy
pipeline, rather than introducing additional complexity to deal
with it.

Differential Revision: https://reviews.llvm.org/D128536
2022-06-27 09:42:17 +02:00
Florian Hahn fb4113ef0c
[Passes] Remove legacy LoopUnswitch pass.
The legacy LoopUnswitch pass is only used in the legacy pass manager
pipeline, which is deprecated.

The NewPM replacement is SimpleLoopUnswitch and I think it is time to
remove the legacy LoopUnswitch code.

Fixes #31000.

Reviewed By: aeubanks, Meinersbur, asbirlea

Differential Revision: https://reviews.llvm.org/D124376
2022-04-29 10:30:49 +01:00
Chuanqi Xu 483efc9ad0 [Pipelines] Remove Legacy Passes in Coroutines
The legacy passes are deprecated now and would be removed in near
future. This patch tries to remove legacy passes in coroutines.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D123918
2022-04-21 10:59:11 +08:00
Arthur Eubanks 2e6ac54cf4 [LegacyPM] Remove ThinLTO/LTO pipelines
Using the legacy PM for the optimization pipeline was deprecated in 13.0.0.
Following recent changes to remove non-core features of the legacy
PM/optimization pipeline, remove the (Thin)LTO pipelines.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D123882
2022-04-18 10:09:41 -07:00
Mats Larsen ad523cc398
[NFC][Docs] Add missing Doxygen group comments for LLVM-C
The LLVM-C API is relatively small so we've previously added doxygen tags
so it's easier to navigate the LLVM-C web docs. Over the years, more
headers were added without proper doxygen tags, effectively hiding them
from the main LLVM-C doxygen page. This patch adds comments to headers
which did not have them.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D112474
2021-11-07 12:23:17 +01:00
Ben Langmuir 2f53fcc831 Fix compilation errors in C API when using C compiler
* Cannot use sizeof() on another union member
* nullptr vs NULL
* () vs (void)

Incidentally, fix an incorrect comment about memory ownership on the
argument to __orc_rt_CreateCWrapperFunctionResultFromOutOfBandError,
which is copied, not moved.
2021-08-24 10:12:32 -07:00
Chuanqi Xu 8a1727ba51 [Coroutines] Run coroutine passes by default
This patch make coroutine passes run by default in LLVM pipeline. Now
the clang and opt could handle IR inputs containing coroutine intrinsics
without special options.
It should be fine. On the one hand, the coroutine passes seems to be stable
since there are already many projects using coroutine feature.
On the other hand, the coroutine passes should do nothing for IR who doesn't
contain coroutine intrinsic.

Test Plan: check-llvm

Reviewed by: lxfind, aeubanks

Differential Revision: https://reviews.llvm.org/D105877
2021-07-15 14:33:40 +08:00
Mats Larsen 0c557db617 [NewPM] Add C bindings for new pass manager
This patch contains the bare minimum to run the new Pass Manager from the LLVM-C APIs. It does not feature PGOOptions, PassPlugins or Debugify in its current state. Bugzilla: PR48499

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D102136
2021-05-17 11:45:47 -07:00
Nico Weber 0b33977872 Revert "[NewPM] Add C bindings for new pass manager"
This reverts commit cd220a0678.
Doesn't build.
2021-05-17 13:59:12 -04:00
Mats Larsen cd220a0678 [NewPM] Add C bindings for new pass manager
This patch contains the bare minimum to run the new Pass Manager from the LLVM-C APIs. It does not feature PGOOptions, PassPlugins or Debugify in its current state. Bugzilla: PR48499

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D102136
2021-05-17 10:48:45 -07:00
Arthur Eubanks 96f0b57568 [Bindings] Add LLVMAddInstructionSimplifyPass
Reviewed By: sroland

Differential Revision: https://reviews.llvm.org/D86764
2020-09-01 12:38:49 -07:00
Arthur Eubanks 486ed88533 [ConstProp] Remove ConstantPropagation
As discussed in
http://lists.llvm.org/pipermail/llvm-dev/2020-July/143801.html.

Currently no users outside of unit tests.

Replace all instances in tests of -constprop with -instsimplify.
Notable changes in tests:
* vscale.ll - @llvm.sadd.sat.nxv16i8 is evaluated by instsimplify, use a fake intrinsic instead
* InsertElement.ll - insertelement undef is removed by instsimplify in @insertelement_undef
llvm/test/Transforms/ConstProp moved to llvm/test/Transforms/InstSimplify/ConstProp

Reviewed By: lattner, nikic

Differential Revision: https://reviews.llvm.org/D85159
2020-08-26 15:51:30 -07:00
Florian Hahn 599955eb56 Recommit "[IPConstProp] Remove and move tests to SCCP."
This reverts commit 59d6e814ce.

The cause for the revert (3 clang tests running opt -ipconstprop) was
fixed by removing those lines.
2020-08-02 22:23:54 +01:00
Florian Hahn 59d6e814ce Revert "[IPConstProp] Remove and move tests to SCCP."
This reverts commit e77624a3be.

Looks like some clang tests manually invoke -ipconstprop via opt.....
2020-07-30 13:06:54 +01:00
Florian Hahn e77624a3be [IPConstProp] Remove and move tests to SCCP.
As far as I know, ipconstprop has not been used in years and ipsccp has
been used instead. This has the potential for confusion and sometimes
leads people to spend time finding & reporting bugs as well as
updating it to work with the latest API changes.

This patch moves the tests over to SCCP. There's one functional difference
I am aware of: ipconstprop propagates for each call-site individually, so
for functions that are called with different constant arguments it can sometimes
produce better results than ipsccp (at much higher compile-time cost).But
IPSCCP can be thought to do so as well for internal functions and as mentioned
earlier, the pass seems unused in practice (and there are no plans on working
towards enabling it anytime).

Also discussed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2020-July/143773.html

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D84447
2020-07-30 12:36:27 +01:00
Ayke van Laethem 2a7a989c3e
[LLVM-C] Add bindings for addCoroutinePassesToExtensionPoints
This patch adds bindings to C and Go for
addCoroutinePassesToExtensionPoints, which is used to add coroutine
passes to the correct locations in PassManagerBuilder.

Differential Revision: https://reviews.llvm.org/D51642
2020-02-24 20:15:51 +01:00
Brian Gesiak 2fcf7691df [Coroutines] Rename "legacy" passes (NFC)
A series of patches beginning with https://reviews.llvm.org/D71898
propose to add an implementation of the coroutine passes to the new pass
manager. As part of these changes, the coroutine passes that implement
the legacy pass manager interface are renamed, to `<PassName>Legacy`.
This mirrors similar changes that have been made to many other passes in
LLVM as they've been transitioned to support both old and new pass
managers.

This commit splits out the renaming portion of that patch and commits it
in advance as an NFC (no functional change intended) commit. It renames:

* `CoroEarly` => `CoroEarlyLegacy`
* `CoroSplit` => `CoroSplitLegacy`
* `CoroElide` => `CoroElideLegacy`
* `CoroCleanup` => `CoroCleanupLegacy`
2020-01-01 21:41:16 -05:00
Duncan P. N. Exon Smith 8c48405069 Wrap C APIs with pragmas enforcing -Werror=strict-prototypes
Force `-Werror=strict-prototypes` so that C API tests fail to compile if
we add a non-prototype declaration.  This should help avoid regressions
like bddecba4b3 was fixing.

https://reviews.llvm.org/D70285
rdar://problem/57203137
2019-11-19 13:18:43 -08:00
Joerg Sonnenberger 9681ea9560 Reapply r374743 with a fix for the ocaml binding
Add a pass to lower is.constant and objectsize intrinsics

This pass lowers is.constant and objectsize intrinsics not simplified by
earlier constant folding, i.e. if the object given is not constant or if
not using the optimized pass chain. The result is recursively simplified
and constant conditionals are pruned, so that dead blocks are removed
even for -O0. This allows inline asm blocks with operand constraints to
work all the time.

The new pass replaces the existing lowering in the codegen-prepare pass
and fallbacks in SDAG/GlobalISEL and FastISel. The latter now assert
on the intrinsics.

Differential Revision: https://reviews.llvm.org/D65280

llvm-svn: 374784
2019-10-14 16:15:14 +00:00
Dmitri Gribenko 1a21f98ac3 Revert "Add a pass to lower is.constant and objectsize intrinsics"
This reverts commit r374743. It broke the build with Ocaml enabled:
http://lab.llvm.org:8011/builders/clang-x86_64-debian-fast/builds/19218

llvm-svn: 374768
2019-10-14 12:22:48 +00:00
Joerg Sonnenberger e4300c392d Add a pass to lower is.constant and objectsize intrinsics
This pass lowers is.constant and objectsize intrinsics not simplified by
earlier constant folding, i.e. if the object given is not constant or if
not using the optimized pass chain. The result is recursively simplified
and constant conditionals are pruned, so that dead blocks are removed
even for -O0. This allows inline asm blocks with operand constraints to
work all the time.

The new pass replaces the existing lowering in the codegen-prepare pass
and fallbacks in SDAG/GlobalISEL and FastISel. The latter now assert
on the intrinsics.

Differential Revision: https://reviews.llvm.org/D65280

llvm-svn: 374743
2019-10-13 23:00:15 +00:00
Aditya Kumar a6d9d31279 [LLVM-C][Ocaml] Add MergeFunctions and DCE pass
MergeFunctions and DCE pass are missing from OCaml/C-api. This patch
adds them.

Differential Revision: https://reviews.llvm.org/D65071

Reviewers: whitequark, hiraditya, deadalnix

Reviewed By: whitequark

Subscribers: llvm-commits

Tags: #llvm

Authored by: kren1

llvm-svn: 373170
2019-09-29 16:06:22 +00:00
Robert Widmann fcf3c55a8c [LLVM-C] Improve Bindings to The Internalize Pass
Summary: Adds a binding to the internalize pass that allows the caller to pass a function pointer that acts as the visibility-preservation predicate.  Previously, one could only pass an unsigned value (not LLVMBool?) that directed the pass to consider "main" or not.

Reviewers: whitequark, deadalnix, harlanhaskins

Reviewed By: whitequark, harlanhaskins

Subscribers: kren1, hiraditya, llvm-commits, harlanhaskins

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62456

llvm-svn: 366777
2019-07-23 04:56:44 +00:00
Robert Widmann 2f1ebe6ee8 [LLVM-C] Expose the "Add Discriminators" Pass To LLVM-C
Summary: Add bindings to create a wrapped "Add Discriminators" pass.  Now that we have debug info support, this is a handy transform to have.

Reviewers: whitequark, deadalnix

Reviewed By: whitequark

Subscribers: dblaikie, aprantl, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58624

llvm-svn: 356272
2019-03-15 16:57:23 +00:00
Chandler Carruth 2946cd7010 Update the file headers across all of the LLVM projects in the monorepo
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00
whitequark 29b2980159 Revert "[LLVM-C] Add bindings for addCoroutinePassesToExtensionPoints"
This reverts commit c4baf7c2f06ff5459c4f5998ce980346e72bff97.

Broke the bots, and should really be in Transforms/Coroutines
instead.

llvm-svn: 343337
2018-09-28 16:45:18 +00:00
whitequark 937afbc365 [LLVM-C] Add bindings for addCoroutinePassesToExtensionPoints
Summary: This patch adds bindings to C and Go for addCoroutinePassesToExtensionPoints, which is used to add coroutine passes to the correct locations in PassManagerBuilder.

Reviewers: whitequark, deadalnix

Reviewed By: whitequark

Subscribers: mehdi_amini, modocache, llvm-commits

Differential Revision: https://reviews.llvm.org/D51642

llvm-svn: 343336
2018-09-28 16:38:11 +00:00
whitequark e7e14f464c [LLVM-C][OCaml] Add UnifyFunctionExitNodes pass to C and OCaml APIs
Summary:
Adds LLVMAddUnifyFunctionExitNodesPass to expose
createUnifyFunctionExitNodesPass to the C and OCaml APIs.

Reviewers: whitequark, deadalnix

Reviewed By: whitequark

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D52212

llvm-svn: 342476
2018-09-18 13:36:03 +00:00
whitequark 1f50560e56 [LLVM-C][OCaml] Add LowerAtomic pass to C and OCaml APIs
Summary:
Adds LLVMAddLowerAtomicPass to expose createLowerAtomicPass in the C
and OCaml APIs.

Reviewers: whitequark, deadalnix

Reviewed By: whitequark

Subscribers: jfb, llvm-commits

Differential Revision: https://reviews.llvm.org/D52211

llvm-svn: 342475
2018-09-18 13:35:50 +00:00
Benjamin Kramer 837f93af7d [Aggressive InstCombine] Move C bindings to their own header file.
llvm-svn: 341461
2018-09-05 11:41:12 +00:00
whitequark c438ac2352 [LLVM-C] Add coroutine passes
Differential Revision: https://reviews.llvm.org/D50950

llvm-svn: 340147
2018-08-19 23:39:57 +00:00
David Green 963401d2be [UnrollAndJam] New Unroll and Jam pass
This is a simple implementation of the unroll-and-jam classical loop
optimisation.

The basic idea is that we take an outer loop of the form:

  for i..
    ForeBlocks(i)
    for j..
      SubLoopBlocks(i, j)
    AftBlocks(i)

Instead of doing normal inner or outer unrolling, we unroll as follows:

  for i... i+=2
    ForeBlocks(i)
    ForeBlocks(i+1)
    for j..
      SubLoopBlocks(i, j)
      SubLoopBlocks(i+1, j)
    AftBlocks(i)
    AftBlocks(i+1)
  Remainder Loop

So we have unrolled the outer loop, then jammed the two inner loops into
one. This can lead to a simpler inner loop if memory accesses can be shared
between the now jammed loops.

To do this we have to prove that this is all safe, both for the memory
accesses (using dependence analysis) and that ForeBlocks(i+1) can move before
AftBlocks(i) and SubLoopBlocks(i, j).

Differential Revision: https://reviews.llvm.org/D41953

llvm-svn: 336062
2018-07-01 12:47:30 +00:00
Fangrui Song afa95ee03d [LLVM-C] [OCaml] Remove LLVMAddBBVectorizePass
Summary: It was fully replaced back in 2014, and the implementation was removed 11 months ago by r306797.

Reviewers: hfinkel, chandlerc, whitequark, deadalnix

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47436

llvm-svn: 333378
2018-05-28 16:58:10 +00:00
David Green aee7ad0cde Revert 333358 as it's failing on some builders.
I'm guessing the tests reply on the ARM backend being built.

llvm-svn: 333359
2018-05-27 12:54:33 +00:00
David Green 3034281b43 [UnrollAndJam] Add a new Unroll and Jam pass
This is a simple implementation of the unroll-and-jam classical loop
optimisation.

The basic idea is that we take an outer loop of the form:

for i..
  ForeBlocks(i)
  for j..
    SubLoopBlocks(i, j)
  AftBlocks(i)

Instead of doing normal inner or outer unrolling, we unroll as follows:

for i... i+=2
  ForeBlocks(i)
  ForeBlocks(i+1)
  for j..
    SubLoopBlocks(i, j)
    SubLoopBlocks(i+1, j)
  AftBlocks(i)
  AftBlocks(i+1)
Remainder

So we have unrolled the outer loop, then jammed the two inner loops into
one. This can lead to a simpler inner loop if memory accesses can be shared
between the now-jammed loops.

To do this we have to prove that this is all safe, both for the memory
accesses (using dependence analysis) and that ForeBlocks(i+1) can move before
AftBlocks(i) and SubLoopBlocks(i, j).

Differential Revision: https://reviews.llvm.org/D41953

llvm-svn: 333358
2018-05-27 12:11:21 +00:00
David Blaikie a27771b62f InstCombine: Fix layering by not including Scalar.h in InstCombine
(notionally Scalar.h is part of libLLVMScalarOpts, so it shouldn't be
included by InstCombine which doesn't/shouldn't need to depend on
ScalarOpts)

llvm-svn: 330669
2018-04-24 00:48:59 +00:00
Craig Topper 1bcb258ba3 [AggressiveInstCombine] Add aggressive inst combiner to the LLVM C API.
I just tried to copy what was done for regular InstCombine. Hopefully I didn't miss anything.

llvm-svn: 330668
2018-04-24 00:39:29 +00:00
David Blaikie c90289b5d3 llvm-c: Split Utils out of Scalar.h
To fix layering (so that Scalar.h, a libScalarOpts header, isn't
included from Utils - which libScalarOpts depends on).

llvm-svn: 328839
2018-03-29 22:31:38 +00:00
Sanjay Patel b049173157 [SimplifyCFG] use pass options and remove the latesimplifycfg pass
This is no-functional-change-intended.

This is repackaging the functionality of D30333 (defer switch-to-lookup-tables) and 
D35411 (defer folding unconditional branches) with pass parameters rather than a named
"latesimplifycfg" pass. Now that we have individual options to control the functionality,
we could decouple when these fire (but that's an independent patch if desired). 

The next planned step would be to add another option bit to disable the sinking transform
mentioned in D38566. This should also make it clear that the new pass manager needs to
be updated to limit simplifycfg in the same way as the old pass manager.

Differential Revision: https://reviews.llvm.org/D38631

llvm-svn: 316835
2017-10-28 18:43:07 +00:00
Matthew Simpson cb58558c2f Add CalledValuePropagation pass
This patch adds a new pass for attaching !callees metadata to indirect call
sites. The pass propagates values to call sites by performing an IPSCCP-like
analysis using the generic sparse propagation solver. For indirect call sites
having a small set of possible callees, the attached metadata indicates what
those callees are. The metadata can be used to facilitate optimizations like
intersecting the function attributes of the possible callees, refining the call
graph, performing indirect call promotion, etc.

Differential Revision: https://reviews.llvm.org/D37355

llvm-svn: 316576
2017-10-25 13:40:08 +00:00
Chandler Carruth 3545a9e1f9 Remove the BBVectorize pass.
It served us well, helped kick-start much of the vectorization efforts
in LLVM, etc. Its time has come and past. Back in 2014:
http://lists.llvm.org/pipermail/llvm-dev/2014-November/079091.html

Time to actually let go and move forward. =]

I've updated the release notes both about the removal and the
deprecation of the corresponding C API.

llvm-svn: 306797
2017-06-30 07:09:08 +00:00
Joerg Sonnenberger fa7367428a Split the SimplifyCFG pass into two variants.
The first variant contains all current transformations except
transforming switches into lookup tables. The second variant
contains all current transformations.

The switch-to-lookup-table conversion results in code that is more
difficult to analyze and optimize by other passes. Most importantly,
it can inhibit Dead Code Elimination. As such it is often beneficial to
only apply this transformation very late. A common example is inlining,
which can often result in range restrictions for the switch expression.

Changes in execution time according to LNT:
SingleSource/Benchmarks/Misc/fp-convert +3.03%
MultiSource/Benchmarks/ASC_Sequoia/CrystalMk/CrystalMk -11.20%
MultiSource/Benchmarks/Olden/perimeter/perimeter -10.43%
and a couple of smaller changes. For perimeter it also results 2.6%
a smaller binary.

Differential Revision: https://reviews.llvm.org/D30333

llvm-svn: 298799
2017-03-26 06:44:08 +00:00
Davide Italiano 7e274e02ae [GVN] Initial check-in of a new global value numbering algorithm.
The code have been developed by Daniel Berlin over the years, and
the new implementation goal is that of addressing shortcomings of
the current GVN infrastructure, i.e. long compile time for large
testcases, lack of phi predication, no load/store value numbering
etc...

The current code just implements the "core" GVN algorithm, although
other pieces (load coercion, phi handling, predicate system) are
already implemented in a branch out of tree. Once the core is stable,
we'll start adding pieces on top of the base framework.
The test currently living in test/Transform/NewGVN are a copy
of the ones in GVN, with proper `XFAIL` (missing features in NewGVN).
A flag will be added in a future commit to enable NewGVN, so that
interested parties can exercise this code easily.

Differential Revision:  https://reviews.llvm.org/D26224

llvm-svn: 290346
2016-12-22 16:03:48 +00:00
Geoff Berry fcb186ca9d [EarlyCSE] Change C API pass interface for EarlyCSE w/ MemorySSA
Previous change broke the C API for creating an EarlyCSE pass w/
MemorySSA by adding a bool parameter to control whether MemorySSA was
used or not.  This broke the OCaml bindings.  Instead, change the old C
API entry point back and add a new one to request an EarlyCSE pass with
MemorySSA.

llvm-svn: 280379
2016-09-01 15:07:46 +00:00
Geoff Berry 8d84605f25 [EarlyCSE] Optionally use MemorySSA. NFC.
Summary:
Use MemorySSA, if requested, to do less conservative memory dependency
checking.

This change doesn't enable the MemorySSA enhanced EarlyCSE in the
default pipelines, so should be NFC.

Reviewers: dberlin, sanjoy, reames, majnemer

Subscribers: mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D19821

llvm-svn: 280279
2016-08-31 19:24:10 +00:00
David Majnemer cbf614a93b Remove the ScalarReplAggregates pass
Nearly all the changes to this pass have been done while maintaining and
updating other parts of LLVM.  LLVM has had another pass, SROA, which
has superseded ScalarReplAggregates for quite some time.

Differential Revision: http://reviews.llvm.org/D21316

llvm-svn: 272737
2016-06-15 00:19:09 +00:00
Eric Christopher a6b96004b5 Reorganize the C API headers to improve build times.
Type specific declarations have been moved to Type.h and error handling
routines have been moved to ErrorHandling.h. Both are included in Core.h
so nothing should change for projects directly including the headers,
but transitive dependencies may be affected.

llvm-svn: 255965
2015-12-18 01:46:52 +00:00
Hal Finkel 2bb61ba2fe [BDCE] Add a bit-tracking DCE pass
BDCE is a bit-tracking dead code elimination pass. It is based on ADCE (the
"aggressive DCE" pass), with the added capability to track dead bits of integer
valued instructions and remove those instructions when all of the bits are
dead.

Currently, it does not actually do this all-bits-dead removal, but rather
replaces the instruction's uses with a constant zero, and lets instcombine (and
the later run of ADCE) do the rest. Because we essentially get a run of ADCE
"for free" while tracking the dead bits, we also do what ADCE does and removes
actually-dead instructions as well (this includes instructions newly trivially
dead because all bits were dead, but not all such instructions can be removed).

The motivation for this is a case like:

int __attribute__((const)) foo(int i);
int bar(int x) {
  x |= (4 & foo(5));
  x |= (8 & foo(3));
  x |= (16 & foo(2));
  x |= (32 & foo(1));
  x |= (64 & foo(0));
  x |= (128& foo(4));
  return x >> 4;
}

As it turns out, if you order the bit-field insertions so that all of the dead
ones come last, then instcombine will remove them. However, if you pick some
other order (such as the one above), the fact that some of the calls to foo()
are useless is not locally obvious, and we don't remove them (without this
pass).

I did a quick compile-time overhead check using sqlite from the test suite
(Release+Asserts). BDCE took ~0.4% of the compilation time (making it about
twice as expensive as ADCE).

I've not looked at why yet, but we eliminate instructions due to having
all-dead bits in:
External/SPEC/CFP2006/447.dealII/447.dealII
External/SPEC/CINT2006/400.perlbench/400.perlbench
External/SPEC/CINT2006/403.gcc/403.gcc
MultiSource/Applications/ClamAV/clamscan
MultiSource/Benchmarks/7zip/7zip-benchmark

llvm-svn: 229462
2015-02-17 01:36:59 +00:00