Commit Graph

88303 Commits

Author SHA1 Message Date
Eli Bendersky 738fbca845 Fix bug in exception table allocation (PR13678)
Patch by Michael Muller.

llvm-svn: 172214
2013-01-11 16:33:30 +00:00
Tim Northover 3a51aab390 Simplify writing floating types to assembly.
This removes previous special cases for each floating-point type in favour of a
shared codepath.

llvm-svn: 172189
2013-01-11 10:36:13 +00:00
Dmitry Vyukov d08bd13ac8 llvm-symbolizer: add DATA command that allows to symbolize global variables.
Example:
>DATA bin/clang 0x26e8e40
<llvm::SparcSubTypeKV
<40799808 416
The last line is address and size of the object.

llvm-svn: 172180
2013-01-11 07:16:20 +00:00
Nadav Rotem 853fe0acb9 ARM Cost Model: We need to detect the max bitwidth of types in the loop in order to select the max vectorization factor.
We don't have a detailed analysis on which values are vectorized and which stay scalars in the vectorized loop so we use
another method. We look at reduction variables, loads and stores, which are the only ways to get information in and out
of loop iterations. If the data types are extended and truncated then the cost model will catch the cost of the vector
zext/sext/trunc operations.

llvm-svn: 172178
2013-01-11 07:11:59 +00:00
Michael Gottesman 5284bd013f Converted test dont-tce-tail-marked-call.ll to use FileCheck.
llvm-svn: 172172
2013-01-11 04:16:35 +00:00
Michael Gottesman 93a0d49c7e This commit is a 4x squash commit consisting of 4x functions converted to use FileCheck instead of grep.
Messages:
Converted test case trivial_codegen_tailcall.ll to use FileCheck.
Converted test return_constant.ll to use FileCheck instead of grep.
Converted test reorder_load.ll to use FileCheck instead of grep.
Converted test intervening-inst.ll to use FileCheck instead of grep.

llvm-svn: 172171
2013-01-11 04:12:53 +00:00
NAKAMURA Takumi 2abe564806 Revert r172153, "llvm/lib/MC/MCParser/AsmParser.cpp: [ms-inline-asm] Fix a couple of undefined behaviors. Operand->needAddressOf() is not initialized at !Operand->isReg()."
It has been redundant since r172157.

llvm-svn: 172166
2013-01-11 02:50:09 +00:00
Jordan Rose ceb1dbb41f SMDiagnostic: don't emit ranges if there are /any/ multibyte characters.
Right now, only OS X has a way to determine the column width of a string
(PR14910). Until we have a good way to deal with this, we just won't
print carets, source ranges, or fixits for SMDiagnostic if the source line
has multibyte characters in it.

llvm-svn: 172164
2013-01-11 02:37:55 +00:00
Sean Silva 92a44897a2 docs: Fix long standing linking antipattern.
Before we learned about :doc:, we used :ref: and put a dummy link at the
top of each page. Don't do that anymore.

This fixes PR14891 as a special case.

llvm-svn: 172162
2013-01-11 02:28:08 +00:00
Sean Silva 216ff2ff29 docs: fix misleading description.
PR14890

llvm-svn: 172160
2013-01-11 01:54:16 +00:00
Michael Ilseman 6c6d715c15 Support for half intrinsics. Pushes MMX into slower encoding path.
llvm-svn: 172159
2013-01-11 01:45:05 +00:00
NAKAMURA Takumi 7f25427686 X86AsmParser.cpp: Fix up r172148, to add initializer in another CreateMem().
llvm-svn: 172157
2013-01-11 01:13:54 +00:00
Dmitri Gribenko 12e2f2a573 Add a new portability macro LLVM_FUNCTION_NAME, that expands to __func__, if
supported.

llvm-svn: 172156
2013-01-11 01:13:51 +00:00
Jakub Staszak 01fa2d8f13 LoopPass.h doesn't require Function.h. Remove unneeded #include.
llvm-svn: 172155
2013-01-11 01:03:32 +00:00
NAKAMURA Takumi 84f349397c llvm/lib/MC/MCParser/AsmParser.cpp: [ms-inline-asm] Fix a couple of undefined behaviors. Operand->needAddressOf() is not initialized at !Operand->isReg().
llvm-svn: 172153
2013-01-11 00:37:35 +00:00
Jakub Staszak ab3d878f35 Remove heavy and unused #inclues from X86TargetObjectFile.cpp.
llvm-svn: 172151
2013-01-10 23:43:56 +00:00
Eli Bendersky 4d21fa05f7 Rename enumerations s/VK/DK/ to conform to naming convention
llvm-svn: 172149
2013-01-10 23:40:56 +00:00
Chad Rosier 8c2a9c744e [ms-inline asm] Make sure we set a default value for AddressOf. Follow on to
r172121.

llvm-svn: 172148
2013-01-10 23:39:07 +00:00
Eli Bendersky 930f73a0dd fix comments a bit
llvm-svn: 172146
2013-01-10 23:32:57 +00:00
Shuxin Yang c5c730b0e0 PR14904: Segmentation fault running pass 'Recognize loop idioms'
The root cause is mistakenly taking for granted that 
    "dyn_cast<Instruction>(a-Value)"
return a non-NULL instruction.

llvm-svn: 172145
2013-01-10 23:32:01 +00:00
Evan Cheng 098d7b76b0 CastInst::castIsValid should return true if the dest type is the same as
Value's current type. The casting is trivial even for aggregate type.

llvm-svn: 172143
2013-01-10 23:22:53 +00:00
NAKAMURA Takumi e46e8225f4 llvm/test/CodeGen/X86/ms-inline-asm.ll: Fixup; Globals doesn't have leading underscore in symbol on linux.
llvm-svn: 172139
2013-01-10 23:02:48 +00:00
Bob Wilson 81f6babd58 Update Apple's build script for llvmCore. <rdar://problem/12914321>
This change is basically just copying changes that we've used for Apple's
clang builds to the script used for building llvmCore. Besides cleaning it
up to use xcrun to locate the proper versions of tools, especially for cross
compiling, it fixes the build to work with newer versions of clang that
honor SDKROOT settings in the environment.

llvm-svn: 172138
2013-01-10 22:59:51 +00:00
Eli Bendersky ec9e3cff22 Remove a couple of if-else chains in parsing directives, replacing them by a
switch. Committed with Jim's and Chris's approval.

llvm-svn: 172136
2013-01-10 22:44:57 +00:00
Michael J. Spencer d857c1c9bf [llvm-objdump] Emit addresses with the correct number of leading 0's.
llvm-svn: 172130
2013-01-10 22:40:50 +00:00
Peter Collingbourne f7d65c43d0 [msan] Change va_start/va_copy shadow memset alignment to 8.
This fixes va_start/va_copy of a va_list field which happens to not
be laid out at a 16-byte boundary.

Differential Revision: http://llvm-reviews.chandlerc.com/D276

llvm-svn: 172128
2013-01-10 22:36:33 +00:00
Jakub Staszak acd9ab67dc Remove trailing spaces.
llvm-svn: 172125
2013-01-10 22:14:33 +00:00
Evan Cheng c8444b159a PR14896: Handle memcpy from constant string where the memcpy size is larger than the string size.
llvm-svn: 172124
2013-01-10 22:13:27 +00:00
Jakub Staszak a9286e931c Remove unneeded includes from FunctionLoweringInfo.h.
llvm-svn: 172123
2013-01-10 22:13:13 +00:00
Chad Rosier a4bc9437a2 [ms-inline asm] Add support for calling functions from inline assembly.
Part of rdar://12991541

llvm-svn: 172121
2013-01-10 22:10:27 +00:00
Jakub Staszak 56df644323 Remove unneeded #includes.
llvm-svn: 172118
2013-01-10 22:07:29 +00:00
Owen Anderson dbf0ca523d Teach InstCombine to hoist FABS and FNEG through FPTRUNC instructions. The application of these operations commutes with the truncation, so we should prefer to do them in the smallest size we can, to save register space, use smaller constant pool entries, etc.
llvm-svn: 172117
2013-01-10 22:06:52 +00:00
Jakub Staszak 929cf5615f Fix indent and remove unneeded #includes in MDBuilder.h.
llvm-svn: 172115
2013-01-10 22:00:36 +00:00
Jakub Staszak 63e77d5ffa Fix #includes after my last commit.
llvm-svn: 172114
2013-01-10 21:56:40 +00:00
Jakub Staszak 32738212f4 Rename LinkAllVMCore.h to LinkAllIR.h since VMCore directory was renamed to IR.
llvm-svn: 172112
2013-01-10 21:55:02 +00:00
Chris Lattner 045a73e62d remove the rest of the "written by" lines in the documentation. It is
against the developer policy to include this sort of thing as SVN blame
already captures this in a far more fine-grained way.

llvm-svn: 172109
2013-01-10 21:24:04 +00:00
Dmitri Gribenko 7b4fb9a65f Replace memcpys by a static_cast and an integral promotion.
llvm-svn: 172108
2013-01-10 21:21:32 +00:00
Dmitri Gribenko ba9d1b5fcd Fix coding style
llvm-svn: 172107
2013-01-10 21:10:44 +00:00
Jakub Staszak 6a3ef9c094 Unbreak tests after regression from r172081.
llvm-svn: 172105
2013-01-10 21:02:05 +00:00
Jordan Rose efd8f80ed5 Add basic fix-its to SMDiagnostic.
Like Clang's FixItHint, SMFixIt represents an insertion, replacement, or
removal of source text. One or more fix-its can be emitted as part of
a diagnostic, and will be printed below the source range line to show the
user how they can fix their code.

Currently, the only client of SMFixIt is clang-tblgen; thus, the tests for
this behavior live in clang/test/TableGen/tg-fixits.td. If/when SMFixIt is
adopted within LLVM itself, those tests should be moved to the LLVM suite.

llvm-svn: 172086
2013-01-10 18:50:15 +00:00
Jordan Rose f12e8a93ee TableGen: Keep track of superclass reference ranges.
def foo : bar;
          ~~~

This allows us to produce more precise diagnostics about a certain
superclass, and even provide fixits.

llvm-svn: 172085
2013-01-10 18:50:11 +00:00
Jordan Rose abdd99b5aa TableGen: record anonymous instantiations of classes.
llvm-svn: 172084
2013-01-10 18:50:05 +00:00
Jakob Stoklund Olesen f0615c71fa Allow hasProperty() to be called on bundle-internal instructions.
When calling hasProperty() on an instruction inside a bundle, it should
always behave as if IgnoreBundle was passed, and just return properties
for the current instruction.

Only attempt to aggregate bundle properties whan asked about the bundle
header.

The assertion fires on existing ARM test cases without this fix.

llvm-svn: 172082
2013-01-10 18:42:44 +00:00
David Greene 4162c2d31b Fix Alias Bug
Use memcpy to do type punning instead of a cast.  A cast or similar
operation through a union breaks strict aliasing rules.

llvm-svn: 172081
2013-01-10 18:17:54 +00:00
Nadav Rotem 6eae65cfac LoopVectorizer: Fix a bug in the vectorization of BinaryOperators. The BinaryOperator can be folded to an Undef, and we don't want to set NSW flags to undef vals.
PR14878

llvm-svn: 172079
2013-01-10 17:34:39 +00:00
Tim Northover b3cfb28e4d Remove locale-dependence of enum mangling and use existing function.
llvm-svn: 172077
2013-01-10 16:47:31 +00:00
Tim Northover 8f1c8ebb0d Make TableGen mangle operand method names before putting in enum.
The purpose of this patch is to allow PredicateMethods to be set to something
like "isUImm<8>", calling a C++ template method to reduce code duplication. For
this to work, the PredicateMethod must be mangled into a valid C++ identifier
for insertion into an enum.

llvm-svn: 172073
2013-01-10 15:17:36 +00:00
Joey Gouly 5fad3e9ad6 Fix a copy/paste error in the IR Linker, casting an ArrayType instead of a VectorType.
llvm-svn: 172054
2013-01-10 10:49:36 +00:00
Joey Gouly 58bf951dec Fix TryToShrinkGlobalToBoolean in GlobalOpt, so that it does not discard address spaces.
llvm-svn: 172051
2013-01-10 10:31:11 +00:00
Sean Silva 8e68b792b4 docs: fix broken link.
PR14889

llvm-svn: 172046
2013-01-10 06:39:37 +00:00
NAKAMURA Takumi acfc1f21d4 Signal.h: Add <cstdio> for FILE*, since r171989.
llvm-svn: 172044
2013-01-10 05:23:59 +00:00
Michael Gottesman a6cb018bb5 [ObjCARC Debug Message] Added debug message when we convert an autorelease into an autoreleaseRV.
llvm-svn: 172034
2013-01-10 02:03:50 +00:00
Douglas Gregor 056eafd420 Fix a race condition in the lock-file manager: once the lock file is
gone, check for the actual file we care about.

llvm-svn: 172033
2013-01-10 02:01:35 +00:00
Douglas Gregor 95585ab6a4 Fix a race condition in llvm::sys::path::unique_file: when we end up
failing to create the unique file because the path doesn't exist,
don't fail if someone else manages to create the path before we do.

llvm-svn: 172032
2013-01-10 01:58:46 +00:00
Jakob Stoklund Olesen 55a7be237e Support headerless bundles in MachineInstr::hasProperty().
This function can still work without a BUNDLE header instruction.

llvm-svn: 172029
2013-01-10 01:29:42 +00:00
Manman Ren 207bcbacca Stack Alignment: throw error if we can't satisfy the minimal alignment
requirement when creating stack objects in MachineFrameInfo.

Add CreateStackObjectWithMinAlign to throw error when the minimal alignment
can't be achieved and to clamp the alignment when the preferred alignment
can't be achieved. Same is true for CreateVariableSizedObject.
Will not emit error in CreateSpillStackObject or CreateStackObject.

As long as callers of CreateStackObject do not assume the object will be
aligned at the requested alignment, we should not have miscompile since
later optimizations which look at the object's alignment will have the correct
information.

rdar://12713765

llvm-svn: 172027
2013-01-10 01:10:10 +00:00
Michael J. Spencer 8c71e9265a [Object][Archive] Fix name handling with bsd style long names.
llvm-svn: 172026
2013-01-10 01:05:34 +00:00
Jakub Staszak 02a3c9b959 Fix include guards so they exactly match file names.
llvm-svn: 172025
2013-01-10 00:45:19 +00:00
Michael J. Spencer 04614ff6ba [Object][Archive] Apparently StringRef::getAsInteger for APInt accepts spaces.
llvm-svn: 172022
2013-01-10 00:07:38 +00:00
Bill Wendling 3b65187d2f Revert s/Raw/getBitMask/g name change. This is possibly causing LTO test hangings.
llvm-svn: 172020
2013-01-09 23:36:50 +00:00
Michael J. Spencer 751fd88eba [Object][Archive] Use uint64_t instead of APInt. It is significantly faster.
llvm-svn: 172015
2013-01-09 22:58:43 +00:00
Joel Jones 5459754d33 Fix description of ARMOperand
llvm-svn: 172011
2013-01-09 22:34:16 +00:00
Nadav Rotem b1791a75cd ARM Cost model: Use the size of vector registers and widest vectorizable instruction to determine the max vectorization factor.
llvm-svn: 172010
2013-01-09 22:29:00 +00:00
David Greene 9ff8d471d6 Disable -Wuninitialized for gcc
If the compiler is gcc, disable variants of -Wuninitialized depending
on the gcc version.  This gets a lot of false positive warnings out of
the build.

Generate a new configure for the gcc -Wno-uninitialized fix.

Pick up -Wno-uninitialized from configure

Add the option -Wno[-maybe]-uninitialized as determined by configure.

llvm-svn: 172006
2013-01-09 22:11:13 +00:00
Evan Cheng 5652a8df32 Fix a DAG combine bug visitBRCOND() is transforming br(xor(x, y)) to br(x != y).
It cahced XOR's operands before calling visitXOR() but failed to update the
operands when visitXOR changed the XOR node.

rdar://12968664

llvm-svn: 171999
2013-01-09 20:56:40 +00:00
Argyrios Kyrtzidis eb9ae76864 Move the internal PrintStackTrace function that is used for llvm::sys::PrintStackTraceOnErrorSignal(),
into a new function llvm::sys::PrintStackTrace, so that it's available to clients for logging purposes.

llvm-svn: 171989
2013-01-09 19:42:40 +00:00
Michael Gottesman c189a392ce [ObjCARC Debug Messages] This is a squashed commit of 3x debug message commits ala echristo's suggestion.
1. Added debug messages when in OptimizeIndividualCalls we move calls into predecessors and then erase the original call.
2. Added debug messages when in the process of moving calls in ObjCARCOpt::MoveCalls we create new RR and delete old RR.
3. Added a debug message when we visit a specific retain instruction in ObjCARCOpt::PerformCodePlacement.

llvm-svn: 171988
2013-01-09 19:23:24 +00:00
Jakob Stoklund Olesen 6922e9ca7e Don't print bundle flags.
The bundle flags are used by MachineBasicBlock::print(), they don't need
to clutter up individual MachineInstrs.

llvm-svn: 171986
2013-01-09 18:35:09 +00:00
Jakob Stoklund Olesen 68d752bf6b Don't require BUNDLE headers in MachineInstr::getBundleSize().
It is possible to build MI bundles that don't begin with a BUNDLE
header. Add support for such bundles, counting all instructions inside
the bundle.

llvm-svn: 171985
2013-01-09 18:28:16 +00:00
Benjamin Kramer 130fcde3e5 LICM: Hoist insertvalue/extractvalue out of loops.
Fixes PR14854.

llvm-svn: 171984
2013-01-09 18:12:03 +00:00
Sergei Larin 3b46d7ea26 Fix a typo in MachineInstr::unbundleFromSucc() method.
llvm-svn: 171983
2013-01-09 17:54:33 +00:00
Adhemerval Zanella 1ae2248e14 PowerPC: EH adjustments
This patch adjust the r171506 to make all DWARF enconding pc-relative
for PPC64. It also adds the R_PPC64_REL32 relocation handling in MCJIT
(since the eh_frame will not generate PIC-relative relocation) and also
adds the emission of stubs created by the TTypeEncoding.

llvm-svn: 171979
2013-01-09 17:08:15 +00:00
Shankar Easwaran 9f64604e74 add hexagon flags in ELF.h
llvm-svn: 171977
2013-01-09 16:34:46 +00:00
David Tweed f42bdf7c77 For some LLVM-as-library uses it is convenient to create a
subclass of TargetMachine which "forwards" all operations to an
existing internal TargetMachine member variable. In the usage context the
specific-machine class derived from TargetMachine is not visible,
only a reference to the generic base class TargetMachine. Although
getSubtargetImpl() is public in specific-machine classes derived from
TargetMachine, the TargetMachine class unfortunately has
getSubtargetImpl() protected (and accessing non-const members makes
abusing getSubtarget() unsuitable). Making it public in the base class
allows this forwarding pattern.

llvm-svn: 171976
2013-01-09 16:21:47 +00:00
Dmitri Gribenko 06358bd078 Configure: if we compile with clang, check that it is not broken
Some linux distibutions (for example, Mageia 2, Fedora 17) ship Clang that is
essentially broken for the end user.  Clang can not find or compile libstdc++
headers.

The issue is that our configure prefers clang over gcc, thus selecting a broken
Clang when a working GCC is available.

Now we detect this issue by compiling a simple program.  If it does not
compile, configure stops with an error suggesting the user to select a
different compiler.

llvm-svn: 171975
2013-01-09 15:25:30 +00:00
Tim Northover ab7689ecee Check whether MCInst operand isImm before calling getImm.
When processing possible aliases, TableGen assumes that if an operand *can* be
an immediate, then it always *will* be. This is incorrect for the AArch64
backend. This patch inserts a check in the generated code to make sure isImm is
true first.

llvm-svn: 171972
2013-01-09 13:32:04 +00:00
Tim Northover f1450d8d7c Refactor to expose RTLIB calls to targets.
fp128 is almost but not quite completely illegal as a type on AArch64. As a
result it needs to have a register class (for argument passing mainly), but all
operations need to be lowered to runtime calls. Currently there's no way for
targets to do this (without duplicating code), as the relevant functions are
hidden in SelectionDAG. This patch changes that.

llvm-svn: 171971
2013-01-09 13:18:15 +00:00
Manuel Klimek 652b9ab7df Incrase the number of parameters for AlignedCharArrayUnion.
We need this to correctly fix ASTMatchers/ASTTypeTraits.h in clang.

llvm-svn: 171965
2013-01-09 10:39:16 +00:00
Bill Wendling f927ad34e7 Alter the hasing computation when inserting into the folding set.
llvm-svn: 171960
2013-01-09 09:26:23 +00:00
Nadav Rotem 3f5825c6c1 add -march to the test
llvm-svn: 171956
2013-01-09 07:04:23 +00:00
Sean Silva cc951b284b tblgen: use an early return to reduce indentation.
llvm-svn: 171954
2013-01-09 05:28:12 +00:00
Nadav Rotem 977e0be4a0 Efficient lowering of vector sdiv when the divisor is a splatted power of two constant.
PR 14848. The lowered sequence is based on the existing sequence the target-independent
DAG Combiner creates for the scalar case.

Patch by Zvi Rackover.

llvm-svn: 171953
2013-01-09 05:14:33 +00:00
Sean Silva cb1a75e730 tblgen: Factor out common code.
llvm-svn: 171951
2013-01-09 04:49:14 +00:00
Eric Christopher bf7bc4966c Last in the series of removing unnecessary '0' arguments for
address space. Reordered the EmitULEB128IntValue arguments to
make this easier.

llvm-svn: 171949
2013-01-09 03:52:05 +00:00
Andrew Trick 9f0b95f260 MIsched: add an ILP window property to machine model.
This was an experimental option, but needs to be defined
per-target. e.g. PPC A2 needs to aggressively hide latency.

I converted some in-order scheduling tests to A2. Hal is working on
more test cases.

llvm-svn: 171946
2013-01-09 03:36:49 +00:00
NAKAMURA Takumi d7678c6af5 [Object, DebugInfo] Make DWARFContext BE-aware.
test/DebugInfo/member-pointers.ll would not fail in targetting BE any more.

llvm-svn: 171943
2013-01-09 02:45:05 +00:00
Sean Silva 45e4147345 TableGen/LangRef: link bang operators into the productionlist
Now BangOperator should be nicely hyperlinked.

Pointed out by Joel Jones.

llvm-svn: 171942
2013-01-09 02:20:31 +00:00
Sean Silva 543fd7f8be TableGen/LangRef: discuss specific C-like escapes
Suggested by Joel Jones.

llvm-svn: 171941
2013-01-09 02:20:30 +00:00
Sean Silva dce94d3bd2 docs: Fix mention of DefmID to MultiClassID.
llvm-svn: 171940
2013-01-09 02:20:24 +00:00
Sean Silva 0657b40b3c Inline this into its only caller.
It's clearer and additionally this gets rid of the usage of `DefmID`,
which doesn't really correspond to anything in the language (it was just
used in the name of this parsing function which parsed a `MultiClassID`
and returned that multiclass's record).

This area of the code still needs a lot of work.

llvm-svn: 171938
2013-01-09 02:17:14 +00:00
Sean Silva 28f3721aa0 tblgen: Reuse function that is 2 lines above.
llvm-svn: 171937
2013-01-09 02:17:13 +00:00
Sean Silva 710c3ae5e6 fix copy-paste-o
llvm-svn: 171936
2013-01-09 02:11:57 +00:00
Sean Silva c95fe2804d docs: Bring TableGen syntax a bit closer to reality.
It's not just def's but actually a limited subset of Object's that are
allowed inside a multiclass.

Spotted by Joel Jones.

llvm-svn: 171935
2013-01-09 02:11:55 +00:00
Eric Christopher e3ab3d0e2c These functions have default arguments of 0 for the last arg. Use
them.

llvm-svn: 171933
2013-01-09 01:57:54 +00:00
Eric Christopher ce0cfce775 These functions have default arguments of 0 for the last arg. Use
them and add one where it seemed obvious that we wanted one.

llvm-svn: 171932
2013-01-09 01:35:34 +00:00
Nadav Rotem 4c66f87e8e ARM Cost Model: Add a basic vectorization unrolling test.
llvm-svn: 171931
2013-01-09 01:29:07 +00:00
Nadav Rotem 30a65bc39e Remove the -licm pass from the loop vectorizer test because the loop vectorizer does it now.
llvm-svn: 171930
2013-01-09 01:20:59 +00:00
Nadav Rotem b696c36fcd Cost Model: Move the 'max unroll factor' variable to the TTI and add initial Cost Model support on ARM.
llvm-svn: 171928
2013-01-09 01:15:42 +00:00
Jakob Stoklund Olesen 5e111fe533 Add a getBundleEnd() function to go with the existing getBundleStart().
This is easier implemented now that bundle flags are symmetric.

llvm-svn: 171927
2013-01-09 01:02:19 +00:00
Shuxin Yang 9ca562e34e Add comment to the definition of Constant::isZeroValue().
(There already has a concise comment to the declaration.)

Thank Eric Christopher for his feedback!

llvm-svn: 171926
2013-01-09 00:53:25 +00:00