Commit Graph

102 Commits

Author SHA1 Message Date
David Blaikie 17364d4e05 DebugInfo+DeadArgElimination: Ensure llvm::Function*s from debug info are updated even when DAE removes both varargs and non-varargs arguments on the same function.
After some stellar (& inspired) help from Reid Kleckner providing a test
case for some rather unstable undefined behavior showing up as
assertions produced by r214761, I was able to fix this issue in DAE
involving the application of both varargs removal, followed by normal
argument removal.

Indeed I introduced this same bug into ArgumentPromotion (r212128) by
copying the code from DAE, and when I fixed the bug in ArgPromo
(r213805) and commented in that patch that I didn't need to address the
same issue in DAE because it was a single pass. Turns out it's two pass,
one for the varargs and one for the normal arguments, so the same fix is
needed (at least during varargs removal). So here it is.

(the observable/net effect of this bug, even when it didn't result in
assertion failure, is that debug info would describe the DAE'd function
in the abstract, but wouldn't provide high/low_pc, variable locations,
line table, etc (it would appear as though the function had been
entirely optimized away), see the original PR14016 for details of the
general problem)

I'm not recommitting the assertion just yet, as there's been another
regression of it since I last tried. It might just be a few test cases
weren't adequately updated after Adrian or Duncan's recent schema
changes.

llvm-svn: 219210
2014-10-07 15:10:23 +00:00
Duncan P. N. Exon Smith 176b691d32 Revert "Revert "DI: Fold constant arguments into a single MDString""
This reverts commit r218918, effectively reapplying r218914 after fixing
an Ocaml bindings test and an Asan crash.  The root cause of the latter
was a tightened-up check in `DILexicalBlock::Verify()`, so I'll file a
PR to investigate who requires the loose check (and why).

Original commit message follows.

--

This patch addresses the first stage of PR17891 by folding constant
arguments together into a single MDString.  Integers are stringified and
a `\0` character is used as a separator.

Part of PR17891.

Note: I've attached my testcases upgrade scripts to the PR.  If I've
just broken your out-of-tree testcases, they might help.

llvm-svn: 219010
2014-10-03 20:01:09 +00:00
Duncan P. N. Exon Smith 786cd049fc Revert "DI: Fold constant arguments into a single MDString"
This reverts commit r218914 while I investigate some bots.

llvm-svn: 218918
2014-10-02 22:15:31 +00:00
Duncan P. N. Exon Smith 571f97bd90 DI: Fold constant arguments into a single MDString
This patch addresses the first stage of PR17891 by folding constant
arguments together into a single MDString.  Integers are stringified and
a `\0` character is used as a separator.

Part of PR17891.

Note: I've attached my testcases upgrade scripts to the PR.  If I've
just broken your out-of-tree testcases, they might help.

llvm-svn: 218914
2014-10-02 21:56:57 +00:00
Adrian Prantl 87b7eb9d0f Move the complex address expression out of DIVariable and into an extra
argument of the llvm.dbg.declare/llvm.dbg.value intrinsics.

Previously, DIVariable was a variable-length field that has an optional
reference to a Metadata array consisting of a variable number of
complex address expressions. In the case of OpPiece expressions this is
wasting a lot of storage in IR, because when an aggregate type is, e.g.,
SROA'd into all of its n individual members, the IR will contain n copies
of the DIVariable, all alike, only differing in the complex address
reference at the end.

By making the complex address into an extra argument of the
dbg.value/dbg.declare intrinsics, all of the pieces can reference the
same variable and the complex address expressions can be uniqued across
the CU, too.
Down the road, this will allow us to move other flags, such as
"indirection" out of the DIVariable, too.

The new intrinsics look like this:
declare void @llvm.dbg.declare(metadata %storage, metadata %var, metadata %expr)
declare void @llvm.dbg.value(metadata %storage, i64 %offset, metadata %var, metadata %expr)

This patch adds a new LLVM-local tag to DIExpressions, so we can detect
and pretty-print DIExpression metadata nodes.

What this patch doesn't do:

This patch does not touch the "Indirect" field in DIVariable; but moving
that into the expression would be a natural next step.

http://reviews.llvm.org/D4919
rdar://problem/17994491

Thanks to dblaikie and dexonsmith for reviewing this patch!

Note: I accidentally committed a bogus older version of this patch previously.
llvm-svn: 218787
2014-10-01 18:55:02 +00:00
Adrian Prantl b458dc2eee Revert r218778 while investigating buldbot breakage.
"Move the complex address expression out of DIVariable and into an extra"

llvm-svn: 218782
2014-10-01 18:10:54 +00:00
Adrian Prantl 25a7174e7a Move the complex address expression out of DIVariable and into an extra
argument of the llvm.dbg.declare/llvm.dbg.value intrinsics.

Previously, DIVariable was a variable-length field that has an optional
reference to a Metadata array consisting of a variable number of
complex address expressions. In the case of OpPiece expressions this is
wasting a lot of storage in IR, because when an aggregate type is, e.g.,
SROA'd into all of its n individual members, the IR will contain n copies
of the DIVariable, all alike, only differing in the complex address
reference at the end.

By making the complex address into an extra argument of the
dbg.value/dbg.declare intrinsics, all of the pieces can reference the
same variable and the complex address expressions can be uniqued across
the CU, too.
Down the road, this will allow us to move other flags, such as
"indirection" out of the DIVariable, too.

The new intrinsics look like this:
declare void @llvm.dbg.declare(metadata %storage, metadata %var, metadata %expr)
declare void @llvm.dbg.value(metadata %storage, i64 %offset, metadata %var, metadata %expr)

This patch adds a new LLVM-local tag to DIExpressions, so we can detect
and pretty-print DIExpression metadata nodes.

What this patch doesn't do:

This patch does not touch the "Indirect" field in DIVariable; but moving
that into the expression would be a natural next step.

http://reviews.llvm.org/D4919
rdar://problem/17994491

Thanks to dblaikie and dexonsmith for reviewing this patch!

llvm-svn: 218778
2014-10-01 17:55:39 +00:00
Reid Kleckner 3715461b48 musttail: Don't eliminate varargs packs if there is a forwarding call
Also clean up and beef up this grep test for the feature.

llvm-svn: 216425
2014-08-26 00:59:51 +00:00
David Majnemer c4ab61cb2f IR: Change inalloca's grammar a bit
The grammar for LLVM IR is not well specified in any document but seems
to obey the following rules:

 - Attributes which have parenthesized arguments are never preceded by
   commas.  This form of attribute is the only one which ever has
   optional arguments.  However, not all of these attributes support
   optional arguments: 'thread_local' supports an optional argument but
   'addrspace' does not.  Interestingly, 'addrspace' is documented as
   being a "qualifier".  What constitutes a qualifier?  I cannot find a
   definition.

 - Some attributes use a space between the keyword and the value.
   Examples of this form are 'align' and 'section'.  These are always
   preceded by a comma.

 - Otherwise, the attribute has no argument.  These attributes do not
   have a preceding comma.

Sometimes an attribute goes before the instruction, between the
instruction and it's type, or after it's type.  'atomicrmw' has
'volatile' between the instruction and the type while 'call' has 'tail'
preceding the instruction.

With all this in mind, it seems most consistent for 'inalloca' on an
'inalloca' instruction to occur before between the instruction and the
type.  Unlike the current formulation, there would be no preceding
comma.  The combination 'alloca inalloca' doesn't look particularly
appetizing, perhaps a better spelling of 'inalloca' is down the road.

llvm-svn: 203376
2014-03-09 06:41:58 +00:00
Nico Rieck 7647178738 Fix broken CHECK lines
llvm-svn: 201479
2014-02-16 07:31:05 +00:00
Reid Kleckner d47a59a4f8 inalloca: Don't remove dead arguments in the presence of inalloca args
It disturbs the layout of the parameters in memory and registers,
leading to problems in the backend.

The plan for optimizing internal inalloca functions going forward is to
essentially SROA the argument memory and demote any captured arguments
(things that aren't trivially written by a load or store) to an indirect
pointer to a static alloca.

llvm-svn: 200717
2014-02-03 20:42:49 +00:00
Manman Ren 409558f81e Debug Info: update testing cases to specify the debug info version number.
We are going to drop debug info without a version number or with a different
version number, to make sure we don't crash when we see bitcode files with
different debug info metadata format.

llvm-svn: 195504
2013-11-22 21:49:45 +00:00
Shuxin Yang 1cab418ce2 Fix a bug in Dead Argument Elimination.
If a function seen at compile time is not necessarily the one linked to
the binary being built, it is illegal to change the actual arguments
passing to it. 

  e.g. 
   --------------------------
   void foo(int lol) {
     // foo() has linkage satisifying isWeakForLinker()
     // "lol" is not used at all.
   }

   void bar(int lo2) {
      // xform to foo(undef) is illegal, as compiler dose not know which
      // instance of foo() will be linked to the the binary being built.
      foo(lol2); 
   }
  -----------------------------

  Such functions can be captured by isWeakForLinker(). NOTE that
mayBeOverridden() is insufficient for this purpose as it dosen't include
linkage types like AvailableExternallyLinkage and LinkOnceODRLinkage.
Take link_odr* as an example, it indicates a set of *EQUIVALENT* globals
that can be merged at link-time. However, the semantic of 
*EQUIVALENT*-functions includes parameters. Changing parameters breaks
the assumption.

  Thank John McCall for help, especially for the explanation of subtle
difference between linkage types.

  rdar://11546243

llvm-svn: 192302
2013-10-09 17:21:44 +00:00
Manman Ren f2a88f3622 Debug Info Testing: update context from empty string to null.
Context should be either null or MDNode.

llvm-svn: 190267
2013-09-08 03:11:54 +00:00
Manman Ren deeafd8a58 Debug Info Testing: updated to use NULL instead of "i32 0" in a few fields.
Field 2 of DIType (Context), field 9 of DIDerivedType (TypeDerivedFrom),
field 12 of DICompositeType (ContainingType), fields 2, 7, 12 of DISubprogram
(Context, Type, ContainingType).

llvm-svn: 190205
2013-09-06 21:03:58 +00:00
Manman Ren 0ed70aeb85 Debug Info: add an identifier field to DICompositeType.
DICompositeType will have an identifier field at position 14. For now, the
field is set to null in DIBuilder.
For DICompositeTypes where the template argument field (the 13th field)
was optional, modify DIBuilder to make sure the template argument field is set.
Now DICompositeType has 15 fields.

Update DIBuilder to use NULL instead of "i32 0" for null value of a MDNode.
Update verifier to check that DICompositeType has 15 fields and the last
field is null or a MDString.

Update testing cases to include an extra field for DICompositeType.
The identifier field will be used by type uniquing so a front end can
genearte a DICompositeType with a unique identifer.

llvm-svn: 189282
2013-08-26 22:39:55 +00:00
Daniel Dunbar 9efbedfd35 [tests] Cleanup initialization of test suffixes.
- Instead of setting the suffixes in a bunch of places, just set one master
   list in the top-level config. We now only modify the suffix list in a few
   suites that have one particular unique suffix (.ml, .mc, .yaml, .td, .py).

 - Aside from removing the need for a bunch of lit.local.cfg files, this enables
   4 tests that were inadvertently being skipped (one in
   Transforms/BranchFolding, a .s file each in DebugInfo/AArch64 and
   CodeGen/PowerPC, and one in CodeGen/SI which is now failing and has been
   XFAILED).

 - This commit also fixes a bunch of config files to use config.root instead of
   older copy-pasted code.

llvm-svn: 188513
2013-08-16 00:37:11 +00:00
Manman Ren b75e0c92f3 Debug Info Finder|Verifier: handle DbgLoc attached to instructions.
Also remove checking of llvm.dbg.sp since it is not used in generating dwarf.

Current state of Finder:
DebugInfoFinder tries to list all debug info MDNodes used in a module. To
list debug info MDNodes used by an instruction, DebugInfoFinder provides
processDeclare, processValue and processLocation to handle DbgDeclareInst,
DbgValueInst and DbgLoc attached to instructions. processModule will go
through all DICompileUnits in llvm.dbg.cu and list debug info MDNodes
used by the CUs.

TODO:
1> Finder has a list of CUs, SPs, Types, Scopes and global variables. We
need to add a list of variables that are used by DbgDeclareInst and
DbgValueInst.
2> MDString fields should be null or isa<MDString> and MDNode fields should be
null or isa<MDNode>. We currently use empty string or int 0 to represent null.
3> Go though Verify functions and make sure that they check field types.
4> Clean up existing testing cases to remove llvm.dbg.sp and make sure each
testing case has a llvm.dbg.cu.

Re-apply r187609 with fix to pass ocaml binding. vmcore.ml generates a debug
location with scope being metadata !{}, in verifier we treat this as a null
scope.

llvm-svn: 187812
2013-08-06 19:38:43 +00:00
Eric Christopher cdc78961d3 Temporarily revert "Debug Info Finder|Verifier: handle DbgLoc attached to
instructions." in an attempt to bring back some bots.

This reverts commit r187609.

llvm-svn: 187638
2013-08-02 00:49:44 +00:00
Manman Ren 4c065e779c Debug Info Finder|Verifier: handle DbgLoc attached to instructions.
Also remove checking of llvm.dbg.sp since it is not used in generating dwarf.

Current state of Finder:
DebugInfoFinder tries to list all debug info MDNodes used in a module. To
list debug info MDNodes used by an instruction, DebugInfoFinder provides
processDeclare, processValue and processLocation to handle DbgDeclareInst,
DbgValueInst and DbgLoc attached to instructions. processModule will go
through all DICompileUnits in llvm.dbg.cu and list debug info MDNodes
used by the CUs.

TODO:
1> Finder has a list of CUs, SPs, Types, Scopes and global variables. We
need to add a list of variables that are used by DbgDeclareInst and
DbgValueInst.
2> MDString fields should be null or isa<MDString> and MDNode fields should be
null or isa<MDNode>. We currently use empty string or int 0 to represent null.
3> Go though Verify functions and make sure that they check field types.
4> Clean up existing testing cases to remove llvm.dbg.sp and make sure each
testing case has a llvm.dbg.cu.

llvm-svn: 187609
2013-08-01 20:52:39 +00:00
Manman Ren e9a52e18da Debug Info: update testing cases to pass verifier.
llvm-svn: 187362
2013-07-29 18:12:58 +00:00
Rafael Espindola cb9afe9ad7 Current batch of -disable-debug-info-verifier.
llvm-svn: 187130
2013-07-25 17:16:05 +00:00
Rafael Espindola b552086fcb add -disable-debug-info-verifier to 3 test to fix tests with pipefail.
llvm-svn: 187064
2013-07-24 18:44:10 +00:00
Stephen Lin a76289aa1b Catch more CHECK that can be converted to CHECK-LABEL in Transforms for easier debugging. No functionality change.
This conversion was done with the following bash script:

  find test/Transforms -name "*.ll" | \
  while read NAME; do
    echo "$NAME"
    if ! grep -q "^; *RUN: *llc" $NAME; then
      TEMP=`mktemp -t temp`
      cp $NAME $TEMP
      sed -n "s/^define [^@]*@\([A-Za-z0-9_]*\)(.*$/\1/p" < $NAME | \
      while read FUNC; do
        sed -i '' "s/;\(.*\)\([A-Za-z0-9_]*\):\( *\)define\([^@]*\)@$FUNC\([( ]*\)\$/;\1\2-LABEL:\3define\4@$FUNC(/g" $TEMP
      done
      mv $TEMP $NAME
    fi
  done

llvm-svn: 186269
2013-07-14 01:50:49 +00:00
Stephen Lin c1c7a1309c Update Transforms tests to use CHECK-LABEL for easier debugging. No functionality change.
This update was done with the following bash script:

  find test/Transforms -name "*.ll" | \
  while read NAME; do
    echo "$NAME"
    if ! grep -q "^; *RUN: *llc" $NAME; then
      TEMP=`mktemp -t temp`
      cp $NAME $TEMP
      sed -n "s/^define [^@]*@\([A-Za-z0-9_]*\)(.*$/\1/p" < $NAME | \
      while read FUNC; do
        sed -i '' "s/;\(.*\)\([A-Za-z0-9_]*\):\( *\)@$FUNC\([( ]*\)\$/;\1\2-LABEL:\3@$FUNC(/g" $TEMP
      done
      mv $TEMP $NAME
    fi
  done

llvm-svn: 186268
2013-07-14 01:42:54 +00:00
Stephen Lin 764d8d3d6f Start using CHECK-LABEL in some tests.
llvm-svn: 186163
2013-07-12 14:54:12 +00:00
Stephen Lin 2e551adcd9 DeadArgumentElimination: keep return value on functions that have a live argument with the 'returned' attribute (rather than generate invalid IR); however, if both can be eliminated, both will be
llvm-svn: 185290
2013-06-30 20:26:21 +00:00
Derek Schuff ec9dc01b33 Fix DeleteDeadVarargs not to crash on functions referenced by BlockAddresses
This pass was assuming that if hasAddressTaken() returns false for a
function, the function's only uses are call sites.  That's not true
because there can be references by BlockAddresses too.

Fix the pass to handle this case.  Fix
BlockAddress::replaceUsesOfWithOnConstant() to allow a function's type
to be changed by RAUW'ing the function with a bitcast of the recreated
function.

Patch by Mark Seaborn.

llvm-svn: 183933
2013-06-13 19:51:17 +00:00
Tim Northover 64280fbba1 Make DeadArgumentElimination more conservative on variadic functions
Variadic functions are particularly fragile in the face of ABI changes, so this
limits how much the pass changes them

llvm-svn: 183625
2013-06-09 02:17:27 +00:00
David Blaikie f55abeaf4c Revert "Revert "PR14606: debug info imported_module support""
This reverts commit r179840 with a fix to test/DebugInfo/two-cus-from-same-file.ll

I'm not sure why that test only failed on ARM & MIPS and not X86 Linux, even
though the debug info was clearly invalid on all of them, but this ought to fix
it.

llvm-svn: 179996
2013-04-22 06:12:31 +00:00
Eric Christopher 0e89ade8ff Revert "PR14606: debug info imported_module support"
This reverts commit r179836 as it seems to have caused test failures.

llvm-svn: 179840
2013-04-19 07:47:16 +00:00
David Blaikie 88564f3cf7 PR14606: debug info imported_module support
Adding another CU-wide list, in this case of imported_modules (since they
should be relatively rare, it seemed better to add a list where each element
had a "context" value, rather than add a (usually empty) list to every scope).
This takes care of DW_TAG_imported_module, but to fully address PR14606 we'll
need to expand this to cover DW_TAG_imported_declaration too.

llvm-svn: 179836
2013-04-19 06:57:04 +00:00
David Blaikie 5692e72f30 Revert "Adding DIImportedModules to DIScopes."
This reverts commit 342d92c7a0adeabc9ab00f3f0d88d739fe7da4c7.

Turns out we're going with a different schema design to represent
DW_TAG_imported_modules so we won't need this extra field.

llvm-svn: 178215
2013-03-28 02:44:59 +00:00
David Blaikie a26d70358f Adding DIImportedModules to DIScopes.
This is just the basic groundwork for supporting DW_TAG_imported_module but I
wanted to commit this before pushing support further into Clang or LLVM so that
this rather churny change is isolated from the rest of the work. The major
churn here is obviously adding another field (within the common DIScope prefix)
to all DIScopes (files, classes, namespaces, lexical scopes, etc). This should
be the last big churny change needed for DW_TAG_imported_module/using directive
support/PR14606.

llvm-svn: 178099
2013-03-27 00:07:26 +00:00
David Blaikie cc8d090163 Remove unused field in DISubprogram
llvm-svn: 177661
2013-03-21 20:28:52 +00:00
David Blaikie 43a729d165 Remove unused field in DICompileUnit
llvm-svn: 177590
2013-03-20 22:34:33 +00:00
David Blaikie 8fb8224578 Split out filename & directory from DIFile to start generalizing over DIScopes
This is the first step to making all DIScopes have a common metadata prefix (so
that things (using directives, for example) that can appear in any scope can be
added to that common prefix). DIFile is itself a DIScope so the common prefix
of all DIScopes cannot be a DIFile - instead it's the raw filename/directory
name pair.

llvm-svn: 177239
2013-03-17 21:13:55 +00:00
David Blaikie 0d221159a0 Remove the unused 4th operand for DIFile debug info metadata
llvm-svn: 176983
2013-03-13 22:05:21 +00:00
David Blaikie 1ca2f36289 Refactor filename/directory in DICompileUnit into a DIFile
This is the next step towards making the metadata for DIScopes have a common
prefix rather than having to delegate based on their tag type.

llvm-svn: 176913
2013-03-13 00:01:35 +00:00
David Blaikie 452c3ff649 Remove unused "isMain" field from DICompileUnit
llvm-svn: 176910
2013-03-12 22:43:04 +00:00
David Blaikie a4f770d51c Update debug info test cases with empty SplitDebugFilename field.
This could be 'null' or the empty string, DIDescriptor::getStringField
coalesces the two cases anyway so it's just a matter of legible/efficient
representation.

The change in behavior of the DICompileUnit::get* functions could be
subsumed by the full verification check - but ideally that should just be an
assertion if we could front-load the actual debug info metadata failure paths.

llvm-svn: 176907
2013-03-12 22:25:36 +00:00
Bill Wendling a032374ea0 Use references to attribute groups on the call/invoke instructions.
Listing all of the attributes for the callee of a call/invoke instruction is way
too much and makes the IR unreadable. Use references to attributes instead.

llvm-svn: 175877
2013-02-22 09:09:42 +00:00
Bill Wendling 90bc19cd91 Modify the LLVM assembly output so that it uses references to represent function attributes.
This makes the LLVM assembly look better. E.g.:

     define void @foo() #0 { ret void }
     attributes #0 = { nounwind noinline ssp }

llvm-svn: 175605
2013-02-20 07:21:42 +00:00
Bill Wendling 84ba97698e FileCheck-ize the tests.
llvm-svn: 174865
2013-02-11 08:34:57 +00:00
David Blaikie 33111dfea0 Remove the (apparently) unnecessary debug info metadata indirection.
The main lists of debug info metadata attached to the compile_unit had an extra
layer of metadata nodes they went through for no apparent reason. This patch
removes that (& still passes just as much of the GDB 7.5 test suite). If anyone
can show evidence as to why these extra metadata nodes are there I'm open to
reverting this patch & documenting why they're there.

llvm-svn: 174266
2013-02-02 05:56:24 +00:00
Dmitri Gribenko d7beca87f5 Tests: rewrite 'opt ... %s' to 'opt ... < %s' so that opt does not emit a ModuleID
This is done to avoid odd test failures, like the one fixed in r171243.

My previous regex was not good enough to find these.

llvm-svn: 171343
2013-01-01 13:57:25 +00:00
Dmitri Gribenko b137c9e551 Tests: rewrite 'opt ... %s' to 'opt ... < %s' so that opt does not emit a ModuleID
This is done to avoid odd test failures, like the one fixed in r171243.

llvm-svn: 171246
2012-12-30 01:28:40 +00:00
Alexey Samsonov 3b861ec989 Fix PR14016.
DeadArgumentElimination pass can replace one LLVM function with another,
invalidating a pointer stored in debug info metadata entry for this function.
To fix this, we collect debug info descriptors for functions before
running a DeadArgumentElimination pass and "patch" pointers in metadata nodes
if we replace a function.

llvm-svn: 165490
2012-10-09 08:13:15 +00:00
Chandler Carruth ff123d5c63 Fix the remaining TCL-style quotes found in the testsuite. This is
another mechanical change accomplished though the power of terrible Perl
scripts.

I have manually switched some "s to 's to make escaping simpler.

While I started this to fix tests that aren't run in all configurations,
the massive number of tests is due to a really frustrating fragility of
our testing infrastructure: things like 'grep -v', 'not grep', and
'expected failures' can mask broken tests all too easily.

Essentially, I'm deeply disturbed that I can change the testsuite so
radically without causing any change in results for most platforms. =/

llvm-svn: 159547
2012-07-02 19:09:46 +00:00
Chandler Carruth a5a29f970e Convert all tests using TCL-style quoting to use shell-style quoting.
This was done through the aid of a terrible Perl creation. I will not
paste any of the horrors here. Suffice to say, it require multiple
staged rounds of replacements, state carried between, and a few
nested-construct-parsing hacks that I'm not proud of. It happens, by
luck, to be able to deal with all the TCL-quoting patterns in evidence
in the LLVM test suite.

If anyone is maintaining large out-of-tree test trees, feel free to poke
me and I'll send you the steps I used to convert things, as well as
answer any painful questions etc. IRC works best for this type of thing
I find.

Once converted, switch the LLVM lit config to use ShTests the same as
Clang. In addition to being able to delete large amounts of Python code
from 'lit', this will also simplify the entire test suite and some of
lit's architecture.

Finally, the test suite runs 33% faster on Linux now. ;]
For my 16-hardware-thread (2x 4-core xeon e5520): 36s -> 24s

llvm-svn: 159525
2012-07-02 12:47:22 +00:00