Commit Graph

300952 Commits

Author SHA1 Message Date
Simon Pilgrim
c39a217412 Fix a clang::driver::ArgStringList usage I missed in rL344398. NFCI.
llvm-svn: 344400
2018-10-12 19:14:43 +00:00
Simon Pilgrim
1d6b938132 Regenerate test. NFCI.
llvm-svn: 344399
2018-10-12 19:03:54 +00:00
Simon Pilgrim
0e50d4c47b Consistently make llvm::opt::ArgStringList usage explicit to try and appease MSVC 2015 buildbots. NFCI.
llvm-svn: 344398
2018-10-12 18:55:36 +00:00
Jim Ingham
9082c1c0c1 Add "v" as well as "var" as an alias for "frame var".
<rdar://problem/40066460>

llvm-svn: 344397
2018-10-12 18:46:02 +00:00
Rui Ueyama
0f3a56c850 Replace assert() with llvm_unreachable because it's obviously a typo.
llvm-svn: 344395
2018-10-12 18:29:30 +00:00
Rui Ueyama
f3fad55787 Remove Type parameter from SymbolTable::insert(). NFC.
`Type` parameter was used only to check for TLS attribute mismatch,
but we can do that when we actually replace symbols, so we don't need
to type as an argument. This change should simplify the interface of
the symbol table a bit.

llvm-svn: 344394
2018-10-12 18:29:18 +00:00
Reid Kleckner
810687cb57 [codeview] Emit S_BUILDINFO and LF_BUILDINFO with cwd and source file
Summary: We can fill in the command line and compiler path later if we want.

Reviewers: zturner

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D53179

llvm-svn: 344393
2018-10-12 18:19:06 +00:00
Andrea Di Biagio
6c17e80265 [llvm-mca] Correctly set aliases for register writes introduced by optimized register moves.
This fixes a problem introduced by r344334. A write from a non-zero move
eliminated at register renaming stage was not correctly handled by the PRF. This
would have led to an assertion failure if the processor model declares a PRF
that enables non-zero move elimination.

llvm-svn: 344392
2018-10-12 18:18:53 +00:00
Jonathan Metzman
0b94e88007 [SanitizerCoverage] Prevent /OPT:REF from stripping constructors
Summary:
Linking with the /OPT:REF linker flag when building COFF files causes
the linker to strip SanitizerCoverage's constructors. Prevent this by
giving the constructors WeakODR linkage and by passing the linker a
directive to include sancov.module_ctor.

Include a test in compiler-rt to verify libFuzzer can be linked using
/OPT:REF

Reviewers: morehouse, rnk

Reviewed By: morehouse, rnk

Subscribers: rnk, morehouse, hiraditya

Differential Revision: https://reviews.llvm.org/D52119

llvm-svn: 344391
2018-10-12 18:11:47 +00:00
Simon Pilgrim
f45bbd4c12 Fix MCBTF string array initialization so its MSVC friendly. NFCI.
llvm-svn: 344390
2018-10-12 18:10:04 +00:00
Reid Kleckner
3185977105 Revert r344375 "[Driver] check for exit code from SIGPIPE"
This doesn't build on Windows.

llvm-svn: 344389
2018-10-12 18:08:11 +00:00
Jonas Toth
20ab6954a4 [Doc] fix second error in UsersManual
llvm-svn: 344388
2018-10-12 17:57:18 +00:00
Fangrui Song
d15d602654 [BPF] Use cstdint {,u}int*_t instead of linux/types.h __u32 __u16 ...
llvm-svn: 344387
2018-10-12 17:57:07 +00:00
Stella Stamenova
073d21fad0 [lldbsuite] Fix the filecheck functionality to work with Python 3
Summary: This is another string/byte conversion issue between Python 2 and 3. In Python 2, the subprocess communication expects a byte string, but in Python 3, it expects bytes. Since both versions are capable of using strings when universal_newlines is set to True AND filecheck operates on strings, force the use of strings.

Reviewers: zturner, asmith, vsk

Reviewed By: zturner

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D53166

llvm-svn: 344386
2018-10-12 17:56:01 +00:00
Eric Liu
0916efc232 Disambiguate: s/make_unique/llvm::make_unique/. NFC
llvm-svn: 344385
2018-10-12 17:55:21 +00:00
Jonas Toth
f79f8eecce [clangd] NFC fix semicolon warning
llvm-svn: 344384
2018-10-12 17:47:43 +00:00
Jonas Toth
30f6c63107 [Doc] fix BB, add code-block type
llvm-svn: 344382
2018-10-12 17:44:01 +00:00
Fangrui Song
19b8fa5c5a [BPF] Don't include linux/types.h and fix style
llvm-svn: 344381
2018-10-12 17:41:12 +00:00
Jonas Toth
6042235450 [doc] fix markup in clang-tidy bugprone-not-null-terminated-result
llvm-svn: 344379
2018-10-12 17:36:04 +00:00
Zachary Turner
4b6f60073a Fix another error related to YAML quoting.
This one occured in polly, which I didn't build / test the first
time so I didn't catch it.

llvm-svn: 344378
2018-10-12 17:28:39 +00:00
Zachary Turner
5bba1cafbe Better support for POSIX paths in PDBs.
This a resubmission of a patch which was previously reverted
due to breaking several lld tests.  The issues causing those
failures have been fixed, so the patch is now resubmitted.

---Original Commit Message---

While it doesn't make a *ton* of sense for POSIX paths to be
in PDBs, it's possible to occur in real scenarios involving
cross compilation.

The tools need to be able to handle this, because certain types
of debugging scenarios are possible without a running process
and so don't necessarily require you to be on a Windows system.
These include post-mortem debugging and binary forensics (e.g.
using a debugger to disassemble functions and examine symbols
without running the process).

There's changes in clang, LLD, and lldb in this patch.  After
this the cross-platform disassembly and source-list tests pass
on Linux.

Furthermore, the behavior of LLD can now be summarized by a much
simpler rule than before: Unless you specify /pdbsourcepath and
/pdbaltpath, the PDB ends up with paths that are valid within
the context of the machine that the link is performed on.

Differential Revision: https://reviews.llvm.org/D53149

llvm-svn: 344377
2018-10-12 17:26:19 +00:00
Fangrui Song
2c31e12d62 [BPF] Some fixes after rL344366
* Move #include outside of namespaces
* Add missing #include
* Add out-of-line virtual destructor to BTFTypeEntry

designated initializers should also be fixed

llvm-svn: 344376
2018-10-12 17:23:25 +00:00
Nick Desaulniers
c7a3e4a478 [Driver] check for exit code from SIGPIPE
Summary:
D53000 adds a special exit code for SIGPIPE (writing to a closed
reader), and rather than print a fatal warning, skips printing the
error.  This can be seen commonly from piping into head, tee, or
split.

Fixes PR25349, rdar://problem/14285346, b/77310947.

Reviewers: jfb

Reviewed By: jfb

Subscribers: cfe-commits, thakis, srhines

Differential Revision: https://reviews.llvm.org/D53001

llvm-svn: 344375
2018-10-12 17:22:46 +00:00
Jonas Toth
78886233b3 [clang-tidy] New checker for not null-terminated result caused by strlen(), size() or equal length
New checker called bugprone-not-null-terminated-result. This check finds function calls where it is possible to cause a not null-terminated result. Usually the proper length of a string is strlen(src) + 1 or equal length of this expression, because the null terminator needs an extra space. Without the null terminator it can result in undefined behaviour when the string is read.

The following function calls are checked:
memcpy, wmemcpy, memcpy_s, wmemcpy_s, memchr, wmemchr, memmove, wmemmove, memmove_s, wmemmove_s, memset, wmemset, strerror_s, strncmp, wcsncmp, strxfrm, wcsxfrm

The following is a real-world example where the programmer forgot to increase the passed third argument, which is size_t length. That is why the length of the allocated memory is problematic too.

static char *StringCpy(const std::string &str) {
  char *result = reinterpret_cast<char *>(malloc(str.size()));
  memcpy(result, str.data(), str.size());
  return result;
}

After running the tool fix-it rewrites all the necessary code according to the given options. If it is necessary, the buffer size will be increased to hold the null terminator.

static char *StringCpy(const std::string &str) {
  char *result = reinterpret_cast<char *>(malloc(str.size() + 1));
  strcpy(result, str.data());
  return result;
}

Patch by Charusso.

Differential ID: https://reviews.llvm.org/D45050

llvm-svn: 344374
2018-10-12 17:22:36 +00:00
Erik Pilkington
92d8a29ca0 [CodeGen] Handle extern references to OBJC_CLASS_$_*
Some ObjC users declare a extern variable named OBJC_CLASS_$_Foo, then use it's
address as a Class. I.e., one could define isInstanceOfF:

BOOL isInstanceOfF(id c) {
  extern void OBJC_CLASS_$_F;
  return [c class] == (Class)&OBJC_CLASS_$_F;
}

This leads to asserts in clang CodeGen if there is an @implementation of F in
the same TU as an instance of this pattern, because CodeGen assumes that a
variable named OBJC_CLASS_$_* has the right type. This commit fixes the problem
by RAUWing the old (incorrectly typed) global with a new global, then removing
the old global.

rdar://45077269

Differential revision: https://reviews.llvm.org/D53154

llvm-svn: 344373
2018-10-12 17:22:10 +00:00
Nick Desaulniers
727891c918 [Support] exit with custom return code for SIGPIPE
Summary:
We tell the user to file a bug report on LLVM right now, and
SIGPIPE isn't LLVM's fault so our error message is wrong.

Allows frontends to detect SIGPIPE from writing to closed readers.
This can be seen commonly from piping into head, tee, or split.

Fixes PR25349, rdar://problem/14285346, b/77310947

Reviewers: jfb

Reviewed By: jfb

Subscribers: majnemer, kristina, llvm-commits, thakis, srhines

Differential Revision: https://reviews.llvm.org/D53000

llvm-svn: 344372
2018-10-12 17:22:07 +00:00
Shafik Yaghmour
aa30268539 Adding support to step into the callable wrapped by libc++ std::function
rdar://problem/14365983

Differential Revision: https://reviews.llvm.org/D52851

llvm-svn: 344371
2018-10-12 17:20:39 +00:00
Louis Dionne
e2441bd268 [NFC][libc++] Fix broken link in comment
llvm-svn: 344369
2018-10-12 17:12:41 +00:00
Rui Ueyama
2e9d40d5f4 [lld] Add more complete support for the INCLUDE command.
Patch by Ian Tessier.

This change adds INCLUDE support to the MEMORY and SECTION commands, and
to output sections, as per:

https://sourceware.org/binutils/docs/ld/File-Commands.html#File-Commands

Differential Revision: https://reviews.llvm.org/D52951

llvm-svn: 344368
2018-10-12 17:07:32 +00:00
Dan Albert
d0fbef9c75 [Driver] Add defaults for Android ARM FPUs.
Summary:
Android mandates that devices have at least vfpv3-d16 until
Marshmallow and NEON after that. Still honor the user's decision, but
raise the defaults for Android targets.

Reviewers: srhines, pirama, javed.absar, kristof.beyls, peter.smith

Reviewed By: peter.smith

Subscribers: peter.smith, rengolin, kristof.beyls, chrib, cfe-commits

Differential Revision: https://reviews.llvm.org/D53121

llvm-svn: 344367
2018-10-12 17:06:31 +00:00
Yonghong Song
6c2327a09e [BPF] Add BTF generation for BPF target
BTF is the debug format for BPF, a kernel virtual machine
and widely used for tracing, networking and security, etc ([1]).

Currently only instruction streams are passed to kernel,
the kernel verifier verifies them before execution. In order to
provide better visibility of bpf programs to user space
tools, some debug information, e.g., function names and
debug line information are desirable for kernel so tools
can get such information with better annotation
for jited instructions for performance or other reasons.

The dwarf is too complicated in kernel and for BPF.
Hence, BTF is designed to be the debug format for BPF ([2]).
Right now, pahole supports BTF for types, which
are generated based on dwarf sections in the ELF file.

In order to annotate performance metrics for jited bpf insns,
it is necessary to pass debug line info to the kernel.
Furthermore, we want to pass the actual code to the
kernel because of the following reasons:

. bpf program typically is small so storage overhead
  should be small.
. in bpf land, it is totally possible that
  an application loads the bpf program into the
  kernel and then that application quits, so
  holding debug info by the user space application
  is not practical.
. having source codes directly kept by kernel
  would ease deployment since the original source
  code does not need ship on every hosts and
  kernel-devel package does not need to be
  deployed even if kernel headers are used.

The only reliable time to get the source code is
during compilation time. This will result in both more
accurate information and easier deployment as
stated in the above.

Another consideration is for JIT. The project like bcc
use MCJIT to compile a C program into bpf insns and
load them to the kernel ([3]). The generated BTF sections
will be readily available for such cases as well.

This patch implemented generation of BTF info in llvm
compiler. The BTF related sections will be generated
when both -target bpf and -g are specified. Two sections
are generated:
  .BTF contains all the type and string information, and
  .BTF.ext contains the func_info and line_info.

The separation is related to how two sections are used
differently in bpf loader, e.g., linux libbpf ([4]).
The .BTF section can be loaded into the kernel directly
while .BTF.ext needs loader manipulation before loading
to the kernel. The format of the each section is roughly
defined in llvm:include/llvm/MC/MCBTFContext.h and
from the implementation in llvm:lib/MC/MCBTFContext.cpp.
A later example also shows the contents in each section.

The type and func_info are gathered during CodeGen/AsmPrinter
by traversing dwarf debug_info. The line_info is
gathered in MCObjectStreamer before writing to
the object file. After all the information is gathered,
the two sections are emitted in MCObjectStreamer::finishImpl.

With cmake CMAKE_BUILD_TYPE=Debug, the compiler can
dump out all the tables except insn offset, which
will be resolved later as relocation records.
The debug type "btf" is used for BTFContext dump.

Dwarf tests the debug info generation with
llvm-dwarfdump to decode the binary sections and
check whether the result is expected. Currently
we do not have such a tool yet. We will implement
btf dump functionality in bpftool ([5]) as the bpftool is
considered the recommended tool for bpf introspection.
The implementation for type and func_info is tested
with linux kernel test cases. The line_info is visually
checked with dump from linux kernel libbpf ([4]) and
checked with readelf dumping section raw data.

Note that the .BTF and .BTF.ext information will not
be emitted to assembly code and there is no assembler
support for BTF either.

In the below, with a clang/llvm built with CMAKE_BUILD_TYPE=Debug,
Each table contents are shown for a simple C program.

  -bash-4.2$ cat -n test.c
     1  struct A {
     2    int a;
     3    char b;
     4  };
     5
     6  int test(struct A *t) {
     7    return t->a;
     8  }
  -bash-4.2$ clang -O2 -target bpf -g -mllvm -debug-only=btf -c test.c
  Type Table:
  [1] FUNC name_off=1 info=0x0c000001 size/type=2
        param_type=3
  [2] INT name_off=12 info=0x01000000 size/type=4
        desc=0x01000020
  [3] PTR name_off=0 info=0x02000000 size/type=4
  [4] STRUCT name_off=16 info=0x04000002 size/type=8
        name_off=18 type=2 bit_offset=0
        name_off=20 type=5 bit_offset=32
  [5] INT name_off=22 info=0x01000000 size/type=1
        desc=0x02000008

  String Table:
  0 :
  1 : test
  6 : .text
  12 : int
  16 : A
  18 : a
  20 : b
  22 : char
  27 : test.c
  34 : int test(struct A *t) {
  58 :   return t->a;

  FuncInfo Table:
  sec_name_off=6
        insn_offset=<Omitted> type_id=1

  LineInfo Table:
  sec_name_off=6
        insn_offset=<Omitted> file_name_off=27 line_off=34 line_num=6 column_num=0
        insn_offset=<Omitted> file_name_off=27 line_off=58 line_num=7 column_num=3
  -bash-4.2$ readelf -S test.o
  ......
    [12] .BTF              PROGBITS         0000000000000000  0000028d
       00000000000000c1  0000000000000000           0     0     1
    [13] .BTF.ext          PROGBITS         0000000000000000  0000034e
       0000000000000050  0000000000000000           0     0     1
    [14] .rel.BTF.ext      REL              0000000000000000  00000648
       0000000000000030  0000000000000010          16    13     8
  ......
  -bash-4.2$

The latest linux kernel ([6]) can already support .BTF with type information.
The [7] has the reference implementation in linux kernel side
to support .BTF.ext func_info. The .BTF.ext line_info support is not
implemented yet. If you have difficulty accessing [6], you can
manually do the following to access the code:

  git clone https://github.com/yonghong-song/bpf-next-linux.git
  cd bpf-next-linux
  git checkout btf

The change will push to linux kernel soon once this patch is landed.

References:
[1]. https://www.kernel.org/doc/Documentation/networking/filter.txt
[2]. https://lwn.net/Articles/750695/
[3]. https://github.com/iovisor/bcc
[4]. https://github.com/torvalds/linux/tree/master/tools/lib/bpf
[5]. https://github.com/torvalds/linux/tree/master/tools/bpf/bpftool
[6]. https://github.com/torvalds/linux
[7]. https://github.com/yonghong-song/bpf-next-linux/tree/btf

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

Differential Revision: https://reviews.llvm.org/D52950

llvm-svn: 344366
2018-10-12 17:01:46 +00:00
Michal Gorny
e67b68f341 [tests] Readd Python binding tests to check-all
Now that both issues found out during the last iteration have been
fixed, reenable the Python binding tests on buildbots.

llvm-svn: 344365
2018-10-12 16:55:44 +00:00
Michal Gorny
4fc27bd937 [python] [tests] Remove cdb lookup failure test
Remove the test checking for compilation db lookup failure.
Since r342228, JSONCompilationDatabasePlugin infers compile commands for
missing files, therefore making the lookup always succeed.

Differential Revision: https://reviews.llvm.org/D53202

llvm-svn: 344364
2018-10-12 16:55:39 +00:00
Sam McCall
cbf497f452 [clangd] Return Command objects from onCodeAction, rather than ad-hoc JSON. NFC
llvm-svn: 344363
2018-10-12 16:51:48 +00:00
Zachary Turner
359544acc7 Fix one additional test broken by the YAML quoting change.
llvm-svn: 344362
2018-10-12 16:41:37 +00:00
Sanjay Patel
e28c8ecd72 [x86] add and use fast horizontal vector math subtarget feature
This is the planned follow-up to D52997. Here we are reducing horizontal vector math codegen 
by default. AMD Jaguar (btver2) should have no difference with this patch because it has 
fast-hops. (If we want to set that bit for other CPUs, let me know.)

The code changes are small, but there are many test diffs. For files that are specifically 
testing for hops, I added RUNs to distinguish fast/slow, so we can see the consequences 
side-by-side. For files that are primarily concerned with codegen other than hops, I just 
updated the CHECK lines to reflect the new default codegen.

To recap the recent horizontal op story:

1. Before rL343727, we were producing hops for all subtargets for a variety of patterns. 
   Hops were likely not optimal for all targets though.
2. The IR improvement in r343727 exposed a hole in the backend hop pattern matching, so 
   we reduced hop codegen for all subtargets. That was bad for Jaguar (PR39195).
3. We restored the hop codegen for all targets with rL344141. Good for Jaguar, but 
   probably bad for other CPUs.
4. This patch allows us to distinguish when we want to produce hops, so everyone can be 
   happy. I'm not sure if we have the best predicate here, but the intent is to undo the 
   extra hop-iness that was enabled by r344141.

Differential Revision: https://reviews.llvm.org/D53095

llvm-svn: 344361
2018-10-12 16:41:02 +00:00
Nick Desaulniers
47bab69a2e [MC][ELF] fix newly added test
Summary:
Reland of
- r344197 "[MC][ELF] compute entity size for explicit sections"
- r344206 "[MC][ELF] Fix section_mergeable_size.ll"
after being reverted in r344278 due to build breakages from not
specifying a target triple.

Move test from test/CodeGen/Generic/ to test/MC/ELF/.
Add explicit target triple so we don't try to run
this test on non ELF targets.

Reported: https://reviews.llvm.org/D53056#1261707

Reviewers: fhahn, rnk, espindola, NoQ

Reviewed By: fhahn, rnk

Subscribers: NoQ, MaskRay, rengolin, emaste, arichardson, llvm-commits, pirama, srhines

Differential Revision: https://reviews.llvm.org/D53146

llvm-svn: 344360
2018-10-12 16:35:44 +00:00
Zachary Turner
9f169afab2 Make YAML quote forward slashes.
If you have the string /usr/bin, prior to this patch it would not
be quoted by our YAML serializer.  But a string like C:\src would
be, due to the presence of a backslash.  This makes the quoting
rules of basically every single file path different depending on
the path syntax (posix vs. Windows).

While technically not required by the YAML specification to quote
forward slashes, when the behavior of paths is inconsistent it
makes it difficult to portably write FileCheck lines that will
work with either kind of path.

Differential Revision: https://reviews.llvm.org/D53169

llvm-svn: 344359
2018-10-12 16:31:20 +00:00
Zachary Turner
9c544199cf Revert "Make YAML quote forward slashes."
This reverts commit b86c16ad8c97dadc1f529da72a5bb74e9eaed344.

This is being reverted because I forgot to write a useful
commit message, so I'm going to resubmit it with an actual
commit message.

llvm-svn: 344358
2018-10-12 16:31:08 +00:00
Zachary Turner
ec234052a6 Make YAML quote forward slashes.
llvm-svn: 344357
2018-10-12 16:24:09 +00:00
Alexey Bataev
9bfe91da3d [OPENMP][NVPTX]Reduce memory usage in orphaned functions.
if the function has globalized variables and called in context of
target/teams/distribute regions, it does not need to globalize 32
copies of the same variables for memory coalescing, it is enough to
have just one copy, because there is parallel region.
Patch does this by adding call for `__kmpc_parallel_level` function and
checking its return value. If the code sees that the parallel level is
0, then only one variable is allocated, not 32.

llvm-svn: 344356
2018-10-12 16:04:20 +00:00
Simon Pilgrim
c046b6856e Pull out repeated value types. NFCI.
llvm-svn: 344355
2018-10-12 15:49:19 +00:00
Simon Pilgrim
b926fd7b36 Pull out repeated value types. NFCI.
llvm-svn: 344354
2018-10-12 15:48:47 +00:00
Sanjay Patel
f5b1892348 [AArch64][x86] add tests for trunc disguised as vector ops (PR39016); NFC
These correspond to the IR transform from:
D52439

llvm-svn: 344353
2018-10-12 15:22:14 +00:00
Simon Pilgrim
0a3bb81974 Fix MSVC 2015 ambiguous symbol warning introduced by rL344337. NFCI.
llvm-svn: 344352
2018-10-12 15:16:25 +00:00
Guillaume Chatelet
946fb0517a [llvm-exegesis][NFC] Simplify code at the cost of small code duplication
Reviewers: courbet

Subscribers: tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D53198

llvm-svn: 344351
2018-10-12 15:12:22 +00:00
Eric Liu
55ab86b72b Fix unused variable warning after r344348
llvm-svn: 344350
2018-10-12 15:01:11 +00:00
Simon Pilgrim
b8339c0167 [SelectionDAG] Move VectorLegalizer::ExpandCTLZ codegen into SelectionDAGLegalize
Generalize SelectionDAGLegalize's CTLZ expansion to handle vectors - lets VectorLegalizer::ExpandCTLZ to just pass the expansion on instead of repeating the same codegen.

llvm-svn: 344349
2018-10-12 14:45:57 +00:00
Simon Pilgrim
78b5a3c3ef [X86][SSE] LowerVectorCTPOP - pull out repeated byte sum stage.
Pull out repeated byte sum stage for popcount of vector elements > 8bits.

This allows us to simplify the LUT/BITMATH popcnt code to always assume vXi8 vectors, and also improves avx512bitalg codegen which only has access to vpopcntb/vpopcntw.

llvm-svn: 344348
2018-10-12 14:18:47 +00:00
Hiroshi Inoue
9552dd187a [PowerPC] avoid masking already-zero bits in BitPermutationSelector
The current BitPermutationSelector generates a code to build a value by tracking two types of bits: ConstZero and Variable.
ConstZero means a bit we need to mask off and Variable is a bit we copy from an input value.

This patch add third type of bits VariableKnownToBeZero caused by AssertZext node or zero-extending load node.
VariableKnownToBeZero means a bit comes from an input value, but it is known to be already zero. So we do not need to mask them.
VariableKnownToBeZero enhances flexibility to group bits, since we can avoid redundant masking for these bits.

This patch also renames "HasZero" to "NeedMask" since now we may skip masking even when we have zeros (of type VariableKnownToBeZero).

Differential Revision: https://reviews.llvm.org/D48025

llvm-svn: 344347
2018-10-12 14:02:20 +00:00