Commit Graph

3096 Commits

Author SHA1 Message Date
Hal Finkel
2bd0acd250 Add local CPU detection for Linux PPC.
This functionality mirrors that available on PPC/Darwin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158314 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-11 15:43:13 +00:00
Hal Finkel
622382fc5e Add POWER6 and POWER7 CPU types to the PPC backend.
No functional change; these will be used by upcoming scheduler enhancements.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158313 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-11 15:43:08 +00:00
Hal Finkel
71ffcfe9f8 Enable ILP scheduling for all nodes by default on PPC.
Over the entire test-suite, this has an insignificantly negative average
performance impact, but reduces some of the worst slowdowns from the
anti-dep. change (r158294).

Largest speedups:
SingleSource/Benchmarks/Stanford/Quicksort - 28%
SingleSource/Benchmarks/Stanford/Towers - 24%
SingleSource/Benchmarks/Shootout-C++/matrix - 23%
MultiSource/Benchmarks/SciMark2-C/scimark2 - 19%
MultiSource/Benchmarks/MiBench/automotive-bitcount/automotive-bitcount - 15%
(matrix and automotive-bitcount were both in the top-5 slowdown list from the
anti-dep. change)

Largest slowdowns:
MultiSource/Benchmarks/McCat/03-testtrie/testtrie - 28%
MultiSource/Benchmarks/mediabench/gsm/toast/toast - 26%
MultiSource/Benchmarks/MiBench/automotive-susan/automotive-susan - 21%
SingleSource/Benchmarks/CoyoteBench/lpbench - 20%
MultiSource/Applications/d/make_dparser - 16%

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158296 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-10 19:32:29 +00:00
Hal Finkel
01a90f4f8f Use critical anti-dep. breaking on all PPC targets, but also add other register classes.
Using 'all' instead of 'critical' would be better because it would make it easier to
satisfy the bundling constraints, but, as noted in the FIXME, that is currently not
possible with the crs.

This yields an average 1% speedup over the entire test suite (on Power 7). Largest speedups:
SingleSource/Benchmarks/Shootout-C++/moments - 40%
MultiSource/Benchmarks/McCat/03-testtrie/testtrie - 28%
SingleSource/Benchmarks/BenchmarkGame/nsieve-bits - 26%
SingleSource/Benchmarks/McGill/misr - 23%
MultiSource/Applications/JM/ldecod/ldecod - 22%

Largest slowdowns:
SingleSource/Benchmarks/Shootout-C++/matrix - -29%
SingleSource/Benchmarks/Shootout-C++/ary3 - -22%
MultiSource/Benchmarks/BitBench/uuencode/uuencode - -18%
SingleSource/Benchmarks/Shootout-C++/ary - -17%
MultiSource/Benchmarks/MiBench/automotive-bitcount/automotive-bitcount - -15%

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158294 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-10 11:15:36 +00:00
Hal Finkel
0a3e33b633 Improve ext/trunc patterns on PPC64.
The PPC64 backend had patterns for i32 <-> i64 extensions and truncations that
would leave self-moves in the final assembly. Replacing those patterns with ones
based on the SUBREG builtins yields better-looking code.

Thanks to Jakob and Owen for their suggestions in this matter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158283 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-09 22:10:19 +00:00
Hal Finkel
8bf75ed41c Enable tail merging on PPC.
Tail merging had been disabled on PPC because it would disturb bundling decisions
made during pre-RA scheduling on the 970 cores. Now, however, all bundling decisions
are made during post-RA scheduling, and tail merging is generally beneficial (the
average test-suite speedup is insignificantly positive).

Largest test-suite speedups:
MultiSource/Benchmarks/mediabench/gsm/toast/toast - 30%
MultiSource/Benchmarks/BitBench/uuencode/uuencode - 23%
SingleSource/Benchmarks/Shootout-C++/ary - 21%
SingleSource/Benchmarks/Stanford/Queens - 17%

Largest slowdowns:
MultiSource/Benchmarks/MiBench/security-sha/security-sha - 24%
MultiSource/Benchmarks/McCat/03-testtrie/testtrie - 22%
MultiSource/Applications/JM/ldecod/ldecod - 14%
MultiSource/Benchmarks/mediabench/g721/g721encode/encode - 9%

This is improved by using full (instead of just critical) anti-dependency breaking,
but doing so still causes miscompiles and so cannot yet be enabled by default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158259 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-09 03:14:50 +00:00
Hal Finkel
16b16ac840 Remove the TODO statement in the PPC README re: CTR loops
As Chris points out, this can now be removed!

TODO: check if the associated section on viterbi's inner loop can also be removed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158224 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-08 20:02:09 +00:00
Hal Finkel
7255d2a808 Enable PPC CTR loop formation by default.
Thanks to Jakob's help, this now causes no new test suite failures!

Over the entire test suite, this gives an average 1% speedup. The largest speedups are:
SingleSource/Benchmarks/Misc/pi - 108%
SingleSource/Benchmarks/CoyoteBench/lpbench - 54%
MultiSource/Benchmarks/Prolangs-C/unix-smail/unix-smail - 50%
SingleSource/Benchmarks/Shootout/ary3 - 32%
SingleSource/Benchmarks/Shootout-C++/matrix - 30%

The largest slowdowns are:
MultiSource/Benchmarks/mediabench/gsm/toast/toast - -30%
MultiSource/Benchmarks/Prolangs-C/bison/mybison - -25%
MultiSource/Benchmarks/BitBench/uuencode/uuencode - -22%
MultiSource/Applications/d/make_dparser - -14%
SingleSource/Benchmarks/Shootout-C++/ary - -13%

In light of these slowdowns, additional profiling work is obviously needed!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158223 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-08 19:19:53 +00:00
Hal Finkel
7e5631202a Mark the PPC CTRRC and CTRRC8 register classes as non-allocatable.
Marking these classes as non-alocatable allows CTR loop generation to
work correctly with the block placement passes, etc. These register
classes are currently used only by some unused TCRETURN patterns.
In future cleanup, these will be removed.

Thanks again to Jakob for suggesting this fix to the CTR loop problem!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158221 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-08 19:02:08 +00:00
Hal Finkel
09fdc7baae Disable the PPC CTR-Loops pass by default.
The pass itself works well, but the something in the Machine* infrastructure
does not understand terminators which define registers. Without the ability
to use the block-placement pass, etc. this causes performance regressions (and
so is turned off by default). Turning off the analysis turns off the problems
with the Machine* infrastructure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158206 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-08 15:38:25 +00:00
Hal Finkel
daa03ec604 Fix a bug in the new PPC CTR-Loops pass.
The code which tests for an induction operation cannot assume that any
ADDI instruction will have a register operand because the operand could
also be a frame index; for example:
    %vreg16<def> = ADDI8 <fi#0>, 0; G8RC:%vreg16

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158205 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-08 15:38:23 +00:00
Hal Finkel
99f823f943 Add the PPCCTRLoops pass: a PPC machine-code-level optimization pass to form CTR-based loop branching code.
This pass is derived from the Hexagon HardwareLoops pass. The only significant enhancement over the Hexagon
pass is that PPCCTRLoops will also attempt to delete the replaced add and compare operations if they are
no longer otherwise used. Also, invalid preheader DebugLoc is not used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158204 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-08 15:38:21 +00:00
Roman Divacky
3e77af4318 PPC32 uses R2 as the TLS register. Fix the copy and paste.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158004 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-05 17:14:17 +00:00
Roman Divacky
fd42ed676e Implement local-exec TLS on PowerPC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157935 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-04 17:36:38 +00:00
Hal Finkel
77a9e0f318 Fix a copy-and-paste duplication error in the PPC 440 and A2 schedules (no functionality change).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157912 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-04 02:39:52 +00:00
Hal Finkel
77838f9ca9 Enable generating PPC pre-increment (r+imm) instructions by default.
It seems that this no longer causes test suite failures on PPC64 (after r157159),
and often gives a performance benefit, so it can be enabled by default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157911 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-04 02:21:00 +00:00
Justin Holewinski
d2ea0e10cb Change interface for TargetLowering::LowerCallTo and TargetLowering::LowerCall
to pass around a struct instead of a large set of individual values.  This
cleans up the interface and allows more information to be added to the struct
for future targets without requiring changes to each and every target.

NV_CONTRIB

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157479 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-25 16:35:28 +00:00
Hal Finkel
2e8e5c0eca Add a missing PPC 64-bit stwu pattern.
This seems to fix the remaining compile-time failures on PPC64 when
compiling with -enable-ppc-preinc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157159 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-20 17:11:24 +00:00
Hal Finkel
b8f2f29467 Add a FIXME about access to negative stack-pointer offsets on PPC32.
The current code will generate a prologue which starts with something like:
        mflr 0
        stw 31, -4(1)
        stw 0, 4(1)
        stwu 1, -16(1)

But under the PPC32 SVR4 ABI, access to negative offsets from R1 is not allowed.

This was pointed out by Peter Bergner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157133 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-19 21:52:55 +00:00
Jim Grosbach
918f55fe23 Allow MCCodeEmitter access to the target MCRegisterInfo.
Add the MCRegisterInfo to the factories and constructors.

Patch by Tom Stellard <Tom.Stellard@amd.com>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156828 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-15 17:35:52 +00:00
Roman Divacky
d9b41b339d Mark .opd @progbits, thus avoiding a warning from asm.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156494 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-09 18:24:23 +00:00
Jakob Stoklund Olesen
397fc4874e Add an MF argument to TRI::getPointerRegClass() and TII::getRegClass().
The getPointerRegClass() hook can return register classes that depend on
the calling convention of the current function (ptr_rc_tailcall).

So far, we have been able to infer the calling convention from the
subtarget alone, but as we add support for multiple calling conventions
per target, that no longer works.

Patch by Yiannis Tsiouris!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156328 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-07 22:10:26 +00:00
Jakob Stoklund Olesen
338607ae0d Remove the SubRegClasses field from RegisterClass descriptions.
This information in now computed by TableGen.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156152 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-04 03:30:34 +00:00
Bill Wendling
7c4ce30ea6 Change the PassManager from a reference to a pointer.
The TargetPassManager's default constructor wants to initialize the PassManager
to 'null'. But it's illegal to bind a null reference to a null l-value. Make the
ivar a pointer instead.
PR12468


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155902 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-01 08:27:43 +00:00
Preston Gurd
6a8c7bf8e7 This patch fixes a problem which arose when using the Post-RA scheduler
on X86 Atom. Some of our tests failed because the tail merging part of
the BranchFolding pass was creating new basic blocks which did not
contain live-in information. When the anti-dependency code in the Post-RA
scheduler ran, it would sometimes rename the register containing
the function return value because the fact that the return value was
live-in to the subsequent block had been lost. To fix this, it is necessary
to run the RegisterScavenging code in the BranchFolding pass.

This patch makes sure that the register scavenging code is invoked
in the X86 subtarget only when post-RA scheduling is being done.
Post RA scheduling in the X86 subtarget is only done for Atom.

This patch adds a new function to the TargetRegisterClass to control
whether or not live-ins should be preserved during branch folding.
This is necessary in order for the anti-dependency optimizations done
during the PostRASchedulerList pass to work properly when doing
Post-RA scheduling for the X86 in general and for the Intel Atom in particular.

The patch adds and invokes the new function trackLivenessAfterRegAlloc()
instead of using the existing requiresRegisterScavenging().
It changes BranchFolding.cpp to call trackLivenessAfterRegAlloc() instead of
requiresRegisterScavenging(). It changes the all the targets that
implemented requiresRegisterScavenging() to also implement
trackLivenessAfterRegAlloc().  

It adds an assertion in the Post RA scheduler to make sure that post RA
liveness information is available when it is needed.

It changes the X86 break-anti-dependencies test to use –mcpu=atom, in order
to avoid running into the added assertion.

Finally, this patch restores the use of anti-dependency checking
(which was turned off temporarily for the 3.1 release) for
Intel Atom in the Post RA scheduler.

Patch by Andy Zhang!

Thanks to Jakob and Anton for their reviews.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155395 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-23 21:39:35 +00:00
Gabor Greif
413ca0d34b effectively back out my last change (r155190)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155195 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-20 11:41:38 +00:00
Gabor Greif
c77d6781d5 fix obviously bogus (IMO) operand index of the load in asserts
(load only has one operand) and smuggle in some whitespace changes too

NB: I am obviously testing the water here, and believe that the unguarded
    cast is still wrong, but why is the getZExtValue of the load's operand
    tested against zero here? Any review is appreciated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155190 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-20 08:58:49 +00:00
Craig Topper
c909950c38 Convert some uses of XXXRegisterClass to &XXXRegClass. No functional change since they are equivalent.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155186 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-20 06:31:50 +00:00
Gabor Greif
a4b00b2db7 zap tabs
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155128 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-19 15:16:31 +00:00
Jay Foad
ef1a3a25b3 Remove unused CCIfSubtarget.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154921 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-17 11:29:05 +00:00
Rafael Espindola
26c8dcc692 Always compute all the bits in ComputeMaskedBits.
This allows us to keep passing reduced masks to SimplifyDemandedBits, but
know about all the bits if SimplifyDemandedBits fails. This allows instcombine
to simplify cases like the one in the included testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154011 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-04 12:51:34 +00:00
Anton Korobeynikov
9cd5e7a478 Make PPCCompilationCallbackC function to be static, so there will be no need to issue call via
PLT when LLVM is built as shared library. This mimics the X86 backend towards the approach.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153938 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-03 06:59:28 +00:00
Hal Finkel
70272aac56 The binutils for the IBM BG/P are too old to support CFI.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153886 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-02 19:09:04 +00:00
Roman Divacky
466958c2a0 Implement the SVR4 byval alignment for aggregates. Fixing a FIXME.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153876 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-02 15:49:30 +00:00
Benjamin Kramer
c97ef618d2 Move getOpcodeName from the various target InstPrinters into the superclass MCInstPrinter.
All implementations used the same code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153866 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-02 08:32:38 +00:00
Craig Topper
7c0b3c1fb6 Remove getInstructionName from MCInstPrinter implementations in favor of using the instruction name table from MCInstrInfo. Reduces static data in the InstPrinter implementations.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153863 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-02 07:01:04 +00:00
Craig Topper
17463b3ef1 Make MCInstrInfo available to the MCInstPrinter. This will be used to remove getInstructionName and the static data it contains since the same tables are already in MCInstrInfo.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153860 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-02 06:09:36 +00:00
Hal Finkel
b66e943d4c Fix some 80-col. violations I introduced with the A2 PPC64 core.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153852 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 21:20:14 +00:00
Hal Finkel
19aa2b5015 Enable prefetch generation on PPC64.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153851 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 20:08:17 +00:00
Hal Finkel
730acfb413 Add LdStSTD* itin. for the PPC64 A2 core.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153850 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 20:08:08 +00:00
Hal Finkel
3f31d492a5 Set the default PPC node scheduling preference to ILP (for the embedded cores).
The 440 and A2 cores have detailed itineraries, and this allows them to be
fully used to maximize throughput.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153845 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 19:23:08 +00:00
Hal Finkel
800125f3a3 Add ppc440 itin. entries for LdStSTD*
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153844 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 19:23:04 +00:00
Hal Finkel
97c9d4c64c Use full anti-dep. breaking with post-ra sched. on the embedded ppc cores.
Post-RA scheduling gives a significant performance improvement on
the embedded cores, so turn it on. Using full anti-dep. breaking is
important for FP-intensive blocks, so turn it on (just on the
embedded cores for now; this should also be good on the 970s because
post-ra scheduling is all that we have for now, but that should have
more testing first).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153843 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 19:22:57 +00:00
Hal Finkel
4d989ac93c Add instruction itinerary for the PPC64 A2 core.
This adds a full itinerary for IBM's PPC64 A2 embedded core. These
cores form the basis for the CPUs in the new IBM BG/Q supercomputer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153842 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 19:22:40 +00:00
Hal Finkel
20b529b3f9 Split the LdStGeneral PPC itin. class into LdStLoad and LdStStore.
Loads and stores can have different pipeline behavior, especially on
embedded chips. This change allows those differences to be expressed.
Except for the 440 scheduler, there are no functionality changes.
On the 440, the latency adjustment is only by one cycle, and so this
probably does not affect much. Nevertheless, it will make a larger
difference in the future and this removes a FIXME from the 440 itin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153821 91177308-0d34-0410-b5e6-96231b3b80d8
2012-04-01 04:44:16 +00:00
Hal Finkel
5b00ceaeea Fix dynamic linking on PPC64.
Dynamic linking on PPC64 has had problems since we had to move the top-down
hazard-detection logic post-ra. For dynamic linking to work there needs to be
a nop placed after every call. It turns out that it is really hard to guarantee
that nothing will be placed in between the call (bl) and the nop during post-ra
scheduling. Previous attempts at fixing this by placing logic inside the
hazard detector only partially worked.

This is now fixed in a different way: call+nop codegen-only instructions. As far
as CodeGen is concerned the pair is now a single instruction and cannot be split.
This solution works much better than previous attempts.

The scoreboard hazard detector is also renamed to be more generic, there is currently
no cpu-specific logic in it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153816 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-31 14:45:15 +00:00
Craig Topper
c89c744b69 Remove unnecessary llvm:: qualifications
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153500 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-27 07:21:54 +00:00
Craig Topper
f1d0f7781e Prune some includes and forward declarations.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153429 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-26 06:58:25 +00:00
Hal Finkel
179a4ddd1f Fix small-integer VAARG on SVR4 ABI PPC64.
The PPC64 SVR4 ABI requires integer stack arguments, and thus the var. args., that
are smaller than 64 bits be zero extended to 64 bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153373 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-24 03:53:55 +00:00
Hal Finkel
f2f6182f6a PPC::DBG_VALUE must use Reg+Imm frame-index elimination even for large offsets. Fixes PR12203.
I don't have a small test case yet, but I'll try to construct one.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153240 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-22 05:28:19 +00:00