Commit Graph

266 Commits

Author SHA1 Message Date
Rafael Espindola
044302d718 Remove an always true argument.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208557 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-12 13:30:10 +00:00
Elena Demikhovsky
1cec507d6d AVX-512: changes in intrinsics
1) Changed gather and scatter intrinsics. Now they are aligned with GCC built-ins. There is no more non-masked form. Masked intrinsic receives -1 if all lanes are executed.
2) I changed the function that works with intrinsics inside X86ISelLowering.cpp. I put all intrinsics in one table. I did it for INTRINSICS_W_CHAIN and plan to put all intrinsics from WO_CHAIN set to the same table in order to avoid the long-long "switch". (I wanted to use static map initialization that allowed by C++11 but I wasn't able to compile it on VS2012).
3) I added gather/scatter prefetch intrinsics.
4) I fixed MRMm encoding for masked instructions.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208522 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-12 07:18:51 +00:00
Rafael Espindola
930ca98433 Fix pr19645.
The fix itself is fairly simple: move getAccessVariant to MCValue so that we
replace the old weak expression evaluation with the far more general
EvaluateAsRelocatable.

This then requires that EvaluateAsRelocatable stop when it finds a non
trivial reference kind. And that in turn requires the ELF writer to look
harder for weak references.

Last but not least, this found a case where we were being bug by bug
compatible with gas and accepting an invalid input. I reported pr19647
to track it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207920 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-03 19:57:04 +00:00
Saleem Abdulrasool
6c76c959e4 MC: create X86WinCOFFStreamer for target specific behaviour
This introduces a target specific streamer, X86WinCOFFStreamer, which handles
the target specific behaviour (e.g. WinEH).  This is mostly to ensure that
differences between ARM and X86 remain disjoint and do not accidentally cross
boundaries.  This is the final staging change for enabling object emission for
Windows on ARM.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207344 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-27 03:48:12 +00:00
Saleem Abdulrasool
64b5470866 X86: convert object streamer selection to a switch
Change the object streamer selection to a switch from a series of if conditions.
Rather than defaulting to ELF, require that an ELF format is requested.  The
Windows/!ELF is maintained as MachO would have been selected first and will
still provide a MachO format.  Add an assertion that if COFF is requested that
the target platform is Windows as only WinCOFF object emission is currently
supported.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207200 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-25 06:29:36 +00:00
Craig Topper
c848b1bbcf [C++] Use 'nullptr'. Target edition.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207197 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-25 05:30:21 +00:00
David Blaikie
45966fa1f1 Spread some const around for non-mutating uses of MCSymbolData.
I discovered this const-hole while attempting to coalesnce the Symbol
and SymbolMap data structures. There's some pending issues with that,
but I figured this change was easy to flush early.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207124 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-24 16:59:40 +00:00
Chandler Carruth
42e8630239 [Modules] Fix potential ODR violations by sinking the DEBUG_TYPE
definition below all of the header #include lines, lib/Target/...
edition.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206842 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-22 02:41:26 +00:00
Chandler Carruth
58f58c97f0 [cleanup] Lift using directives, DEBUG_TYPE definitions, and even some
system headers above the includes of generated '.inc' files that
actually contain code. In a few targets this was already done pretty
consistently, but it wasn't done *really* consistently anywhere. It is
strictly cleaner IMO and necessary in a bunch of places where the
DEBUG_TYPE is referenced from the generated code. Consistency with the
necessary places trumps. Hopefully the build bots are OK with the
movement of intrin.h...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206838 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-22 02:03:14 +00:00
Rafael Espindola
bc26ff9180 Handle _GLOBAL_OFFSET_TABLE_ in 64 bit mode.
With this MC is able to handle _GLOBAL_OFFSET_TABLE_ in 64 bit mode, which is
needed for medium and large code models.

This fixes pr19470.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206793 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-21 21:15:45 +00:00
Rafael Espindola
67f71d14f2 clang-format this function.
No functionality change, it will just make the next patch easier to read.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206792 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-21 21:00:58 +00:00
Jim Grosbach
fdf3f439eb X86: Nuke one more CPU autodetect blurb.
Missed one in r206094. This brings MC and TargetMachine back into sync.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206220 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-14 22:23:30 +00:00
NAKAMURA Takumi
accaa640cf LLVMBuild.txt: Add missing dependencies.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205962 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-10 11:16:47 +00:00
NAKAMURA Takumi
60db02b6fe X86MCAsmInfoGNUCOFF: Set PointerSize as 8 for targeting x64. It caused DW_LNE_set_address was misemitted on x64.
FIXME: I haven't investigate whether CalleeSaveStackSlotSize should be 8.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205772 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-08 15:28:50 +00:00
David Majnemer
2424511b6f X86: Split the relocation selection up
Before, we would have conditional operators where one side of the
operator would be of type RelocationTypeAMD64 and the other is of type
RelocationTypeI386.  GCC would noisly warn with -Wenum-compare
diagnostic.

Instead, refactor the code so it is more like the X86 ELF object writer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205752 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-08 02:15:13 +00:00
Yaron Keren
358d68d383 Correct OS conditionals following r204977 and r204978.
Previously, MinGW OS was Triple::MinGW and Cygwin was Triple::Cygwin
and now it is Triple::Win32 with Environment being GNU or Cygwin.
So,

  TheTriple.getOS() == Triple::Win32 
  
is replaced by

  TheTriple.isWindowsMSVCEnvironment()

and

  (TheTriple.getOS() == Triple::MinGW32 || TheTriple.getOS() == Triple::Cygwin)
  
is replaced by

  TheTriple.isOSCygMing()




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205170 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-31 07:59:14 +00:00
Rafael Espindola
224dbf4aec Completely rewrite ELFObjectWriter::RecordRelocation.
I started trying to fix a small issue, but this code has seen a small fix too
many.

The old code was fairly convoluted. Some of the issues it had:

* It failed to check if a symbol difference was in the some section when
  converting a relocation to pcrel.
* It failed to check if the relocation was already pcrel.
* The pcrel value computation was wrong in some cases (relocation-pc.s)
* It was missing quiet a few cases where it should not convert symbol
  relocations to section relocations, leaving the backends to patch it up.
* It would not propagate the fact that it had changed a relocation to pcrel,
  requiring a quiet nasty work around in ARM.
* It was missing comments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205076 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-29 06:26:49 +00:00
Rafael Espindola
74dcb03fa9 Remove another unused argument.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204961 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-27 20:49:35 +00:00
Rafael Espindola
0c0cd3a4ee Remove unused argument.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204956 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-27 20:41:17 +00:00
Rafael Espindola
0a70f9b3b9 Look through variables when computing relocations.
Given

bar = foo + 4
	.long bar

MC would eat the 4. GNU as includes it in the relocation. The rule seems to be
that a variable that defines a symbol is used in the relocation and one that
does not define a symbol is evaluated and the result included in the relocation.

Fixing this unfortunately required some other changes:

* Since the variable is now evaluated, it would prevent the ELF writer from
  noticing the weakref marker the elf streamer uses. This patch then replaces
  that with a VariantKind in MCSymbolRefExpr.

* Using VariantKind then requires us to look past other VariantKind to see

	.weakref	bar,foo
	call	bar@PLT

  doing this also fixes

	zed = foo +2
	call zed@PLT

  so that is a good thing.

* Looking past VariantKind means that the relocation selection has to use
  the fixup instead of the target.

This is a reboot of the previous fixes for MC. I will watch the sanitizer
buildbot and wait for a build before adding back the previous fixes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204294 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-20 02:12:01 +00:00
Craig Topper
59ae7294ef Prune includes in X86 target.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204216 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-19 06:53:25 +00:00
Rafael Espindola
d1742f6136 Simplify a really complicated check for Arch == X86_64.
The function hasReliableSymbolDifference had exactly one use in the MachO
writer. It is also only true for X86_64. In fact, the comments refers to
"Darwin x86_64" and everything else, so this makes the code match the
comment.

If this is to be abstracted again, it should be a property of
TargetObjectWriter, like useAggressiveSymbolFolding.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203605 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-11 21:22:57 +00:00
Craig Topper
3b89e528c4 [C++11] Remove 'virtual' keyword from methods marked with 'override' keyword.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203444 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-10 05:29:18 +00:00
Craig Topper
124c86ee4a [C++11] Add 'override' keyword to virtual methods that override their base class.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203418 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-09 18:03:14 +00:00
David Majnemer
508e0c4d34 MC: Remove superfluous section attribute flag definitions
Summary:
llvm/MC/MCSectionMachO.h and llvm/Support/MachO.h both had the same
definitions for the section flags.  Instead, grab the definitions out of
support.

No functionality change.

Reviewers: grosbach, Bigcheese, rafael

Reviewed By: rafael

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2998

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203211 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-07 07:36:05 +00:00
Saleem Abdulrasool
4eb048a6f1 Support: split object format out of environment
This is a preliminary setup change to support a renaming of Windows target
triples.  Split the object file format information out of the environment into a
separate entity.  Unfortunately, file format was previously treated as an
environment with an unknown OS.  This is most obvious in the ARM subtarget where
the handling for macho on an arbitrary platform switches to AAPCS rather than
APCS (as per Apple's needs).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203160 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-06 20:47:11 +00:00
Elena Demikhovsky
f4623cee34 AVX-512: fixed comressed displacement - by Robert Khazanov
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203096 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-06 08:15:35 +00:00
Saleem Abdulrasool
86e85c1115 X86: 80-column
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202863 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-04 17:11:46 +00:00
Craig Topper
629b96cb4f Switch all uses of LLVM_OVERRIDE to just use 'override' directly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202621 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-02 09:09:27 +00:00
Craig Topper
fa0cf99585 Remove special FP opcode maps and instead add enough MRM_XX formats to handle all the FP operations. This increases format by 1 bit, but decreases opcode map by 1 bit so the TSFlags size doesn't change.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201649 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-19 08:25:02 +00:00
Craig Topper
52fb0a59d0 Reduce size of map field in X86 TSFlags since it now requires less bits.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201646 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-19 07:29:07 +00:00
Craig Topper
75116bc27e Put some of the X86 formats in a more logical order.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201645 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-19 06:59:13 +00:00
Craig Topper
82a644adf2 Remove A6/A7 opcode maps. They can all be handled with a TB map, opcode of 0xa6/0xa7, and adding MRM_C0/MRM_E0 forms. Removes 376K from the disassembler tables.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201641 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-19 05:34:21 +00:00
Craig Topper
7d2bb38164 Add an x86 prefix encoding for instructions that would decode to a different instruction with 0xf2/f3/66 were in front of them, but don't themselves have a prefix. For now this doesn't change any bbehavior, but plan to use it to fix some bugs in the disassembler.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201538 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-18 00:21:49 +00:00
Daniel Sanders
38c6b58eec Re-commit: Demote EmitRawText call in AsmPrinter::EmitInlineAsm() and remove hasRawTextSupport() call
Summary:
AsmPrinter::EmitInlineAsm() will no longer use the EmitRawText() call for
targets with mature MC support. Such targets will always parse the inline
assembly (even when emitting assembly). Targets without mature MC support
continue to use EmitRawText() for assembly output.

The hasRawTextSupport() check in AsmPrinter::EmitInlineAsm() has been replaced
with MCAsmInfo::UseIntegratedAs which when true, causes the integrated assembler
to parse inline assembly (even when emitting assembly output). UseIntegratedAs
is set to true for targets that consider any failure to parse valid assembly
to be a bug. Target specific subclasses generally enable the integrated
assembler in their constructor. The default value can be overridden with
-no-integrated-as.

All tests that rely on inline assembly supporting invalid assembly (for example,
those that use mnemonics such as 'foo' or 'hello world') have been updated to
disable the integrated assembler.

Changes since review (and last commit attempt):
- Fixed test failures that were missed due to configuration of local build.
  (fixes crash.ll and a couple others).
- Fixed tests that happened to pass because the local build was on X86
  (should fix 2007-12-17-InvokeAsm.ll)
- mature-mc-support.ll's should no longer require all targets to be compiled.
  (should fix ARM and PPC buildbots)
- Object output (-filetype=obj and similar) now forces the integrated assembler
  to be enabled regardless of default setting or -no-integrated-as.
  (should fix SystemZ buildbots)

Reviewers: rafael

Reviewed By: rafael

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2686



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201333 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-13 14:44:26 +00:00
Daniel Sanders
7580df334e Revert r201237+r201238: Demote EmitRawText call in AsmPrinter::EmitInlineAsm() and remove hasRawTextSupport() call
It introduced multiple test failures in the buildbots.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201241 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-12 15:39:20 +00:00
Daniel Sanders
57edb9588b Demote EmitRawText call in AsmPrinter::EmitInlineAsm() and remove hasRawTextSupport() call
Summary:
AsmPrinter::EmitInlineAsm() will no longer use the EmitRawText() call for targets with mature MC support. Such targets will always parse the inline assembly (even when emitting assembly). Targets without mature MC support continue to use EmitRawText() for assembly output.

The hasRawTextSupport() check in AsmPrinter::EmitInlineAsm() has been replaced with MCAsmInfo::UseIntegratedAs which when true, causes the integrated assembler to parse inline assembly (even when emitting assembly output). UseIntegratedAs is set to true for targets that consider any failure to parse valid assembly to be a bug. Target specific subclasses generally enable the integrated assembler in their constructor. The default value can be overridden with -no-integrated-as.

All tests that rely on inline assembly supporting invalid assembly (for example, those that use mnemonics such as 'foo' or 'hello world') have been updated to disable the integrated assembler.

Reviewers: rafael

Reviewed By: rafael

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2686

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201237 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-12 14:44:54 +00:00
Craig Topper
ced2756280 Recommit r201059 and r201060 with hopefully a fix for its original failure.
Original commits messages:

Add MRMXr/MRMXm form to X86 for use by instructions which treat the 'reg' field of modrm byte as a don't care value. Will allow for simplification of disassembler code.

Simplify a bunch of code by removing the need for the x86 disassembler table builder to know about extended opcodes. The modrm forms are sufficient to convey the information.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201065 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-10 06:55:41 +00:00
Bob Wilson
70ff3e91f7 Revert r201059 and r201060.
r201059 appears to cause a crash in a bootstrapped build of clang. Craig
isn't available to look at it right now, so I'm reverting it while he
investigates.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201064 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-10 05:28:30 +00:00
Craig Topper
d8fdb19a7f Add MRMXr/MRMXm form to X86 for use by instructions which treat the 'reg' field of modrm byte as a don't care value. Will allow for simplification of disassembler code.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201059 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-10 00:50:34 +00:00
Rafael Espindola
cc94d006f8 don't set HasReliableSymbolDifference for ELF.
It is only used in MachObjectWriter.cpp. Another leftover from early days
of ELF in MC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200895 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-06 01:06:31 +00:00
Rafael Espindola
b03e2929d3 doesSectionRequireSymbols is meaningless on ELF, remove.
This is a nop. doesSectionRequireSymbols is only used from
isSymbolLinkerVisible. isSymbolLinkerVisible only use from ELF was in

if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
  return false;

if (Symbol.isTemporary())
  return false;

If the symbol is a temporary this code returns false and it is irrelevant if
we take the first if or not. If the symbol is not a temporary,
Asm.isSymbolLinkerVisible returns true without ever calling
doesSectionRequireSymbols.

This was an horrible leftover from when support for ELF was first added.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200894 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-06 00:54:53 +00:00
Elena Demikhovsky
1ee5ca7005 AVX-512: fixed a bug in EVEX encoding (the bug appeared after r200624)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200837 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-05 13:03:01 +00:00
Craig Topper
6b6dfa5c5a Merge x86 HasOpSizePrefix/HasOpSize16Prefix into a 2-bit OpSize field with 0 meaning no 0x66 prefix in any mode. Rename Opsize16->OpSize32 and OpSize->OpSize16. The classes now refer to their operand size rather than the mode in which they need a 0x66 prefix. Hopefully can merge REX_W into this as OpSize64.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200626 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-02 09:25:09 +00:00
Craig Topper
1415ca1781 Merge HasVEXPrefix/HasEVEXPrefix/HasXOPPrefix into a 2-bit 'encoding' field in TSFlags.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200624 91177308-0d34-0410-b5e6-96231b3b80d8
2014-02-02 07:08:01 +00:00
Craig Topper
f0b161d774 Separate x86 opcode maps and 0x66/0xf2/0xf3 prefixes from each other in the TSFlags. This greatly simplifies the switch statements in the disassembler tables and the code emitters.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200522 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-31 08:47:06 +00:00
Craig Topper
45b8e5fa49 Move REP out of the Prefix field of the X86 format. Give it its own bit. It had special handling anyway and this enables a future patch.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200520 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-31 07:00:55 +00:00
Craig Topper
2bb06b0002 Move address override handling in X86MCCodeEmitter to a place where it works for VEX encoded instructions too. This allows 32-bit addressing to work in 64-bit mode.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200516 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-31 05:33:45 +00:00
David Woodhouse
93f81d9b33 [x86] Fix signed relocations for i64i32imm operands
These should end up (in ELF) as R_X86_64_32S relocs, not R_X86_64_32.
Kill the horrid and incomplete special case and FIXME in
EncodeInstruction() and set things up so it can infer the signedness
from the ImmType just like it can the size and whether it's PC-relative.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200495 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-30 22:20:41 +00:00
Rafael Espindola
efdbec8b0a Simplify the handling of iterators in ObjectFile.
None of the object file formats reported error on iterator increment. In
retrospect, that is not too surprising: no object format stores symbols or
sections in a linked list or other structure that requires chasing pointers.
As a consequence, all error checking can be done on begin() and end().

This reduces the text segment of bin/llvm-readobj in my machine from 521233 to
518526 bytes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200442 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-30 02:49:50 +00:00