Commit Graph

411 Commits

Author SHA1 Message Date
Nick Lewycky
398255e70c Use false not zero, as a bool.
llvm-svn: 147292
2011-12-27 18:27:22 +00:00
Nick Lewycky
c554a9b58e Teach simplifycfg to recompute branch weights when merging some branches, and
to discard weights when appropriate. Still more to do (and a new TODO), but
it's a start!

llvm-svn: 147286
2011-12-27 04:31:52 +00:00
Nick Lewycky
8d302df4a4 Update the branch weight metadata when reversing the order of a branch.
llvm-svn: 147280
2011-12-26 20:54:14 +00:00
Nick Lewycky
e87d54c817 Sort includes, canonicalize whitespace, fix typos. No functionality change.
llvm-svn: 147279
2011-12-26 20:37:40 +00:00
Nick Lewycky
b4039f633c Make some intrinsics safe to speculatively execute.
llvm-svn: 147036
2011-12-21 05:52:02 +00:00
Kevin Enderby
8b3deabd2d Revert r146822 at Pete Cooper's request as it broke clang self hosting.
Hope I did this correctly :)

llvm-svn: 146834
2011-12-17 19:48:52 +00:00
Pete Cooper
eadf124d2b SimplifyCFG now predicts some conditional branches to true or false depending on previous branch on same comparison operands.
For example, 

if (a == b) {
    if (a > b) // this is false
    
Fixes some of the issues on <rdar://problem/10554090>

llvm-svn: 146822
2011-12-17 06:32:38 +00:00
Dan Gohman
75d7d5e988 Move Instruction::isSafeToSpeculativelyExecute out of VMCore and
into Analysis as a standalone function, since there's no need for
it to be in VMCore. Also, update it to use isKnownNonZero and
other goodies available in Analysis, making it more precise,
enabling more aggressive optimization.

llvm-svn: 146610
2011-12-14 23:49:11 +00:00
Duncan Sands
29192d042e Delete trivial landing pads that just continue unwinding the caught
exception.

llvm-svn: 139117
2011-09-05 12:57:57 +00:00
Benjamin Kramer
0655b78ccc Address review comments.
- Reword comments.
- Allow undefined behavior interfering with undefined behavior.
- Add address space checks.

llvm-svn: 138619
2011-08-26 02:25:55 +00:00
Benjamin Kramer
fb212a6309 SimplifyCFG: If we have a PHI node that can evaluate to NULL and do a load or store to the address returned by the PHI node then we can consider this incoming value as dead and remove the edge pointing there, unless there are instructions that can affect control flow executed in between.
In theory this could be extended to other instructions, eg. division by zero, but it's likely that it will "miscompile" some code because people depend on div by zero not trapping. NULL pointer dereference usually leads to a crash so we should be on the safe side.

This shrinks the size of a Release clang by 16k on x86_64.

llvm-svn: 138618
2011-08-26 01:22:29 +00:00
Bill Wendling
55d875fa1c I think there was some confusion about what I meant. :-) Replacing the comment.
llvm-svn: 137743
2011-08-16 20:41:17 +00:00
Eli Friedman
bd39703456 After talking with Bill, it seems like the LandingPad handling here is likely
to be wrong (or at least somewhat suspect).  Leave a FIXME for Bill.

llvm-svn: 137694
2011-08-16 00:41:37 +00:00
Eli Friedman
b8f30de527 Minor comment fixes.
llvm-svn: 137693
2011-08-16 00:20:11 +00:00
Eli Friedman
0ffdf2ea0b Update SimplifyCFG for atomic operations.
This commit includes a mention of the landingpad instruction, but it's not
changing the behavior around it.  I think the current behavior is correct,
though.  Bill, can you double-check that?

llvm-svn: 137691
2011-08-15 23:59:28 +00:00
Chris Lattner
229907cd11 land David Blaikie's patch to de-constify Type, with a few tweaks.
llvm-svn: 135375
2011-07-18 04:54:35 +00:00
Jay Foad
5bd375a6cc Convert CallInst and InvokeInst APIs to use ArrayRef.
llvm-svn: 135265
2011-07-15 08:37:34 +00:00
Rafael Espindola
b10a0f223a Add r134057 back, but splice the predecessor after the successors phi
nodes.

Original message:
Let simplify cfg simplify bb with only debug and lifetime intrinsics.

llvm-svn: 134182
2011-06-30 20:14:24 +00:00
Chad Rosier
96ed721d9b Temporarily revert r134057: "Let simplify cfg simplify bb with only debug and
lifetime intrinsics" due to buildbot failures.

llvm-svn: 134071
2011-06-29 16:22:11 +00:00
Rafael Espindola
4c0dfcec7e Let simplify cfg simplify bb with only debug and lifetime intrinsics.
llvm-svn: 134057
2011-06-29 05:25:47 +00:00
Hans Wennborg
4ab4a8e63a Fix PR10103: Less code for enum type translation.
In cases such as the attached test, where the case value for a switch
destination is used in a phi node that follows the destination, it
might be better to replace that value with the condition value of the
switch, so that more blocks can be folded away with
TryToSimplifyUncondBranchFromEmptyBlock because there are less
conflicts in the phi node.

llvm-svn: 133344
2011-06-18 10:28:47 +00:00
Bill Wendling
4f163dfed1 If the block that we're threading through is jumped to by an indirect branch,
then we don't want to set the destination in the indirect branch to the
destination. This is because the indirect branch needs its destinations to have
had their block addresses taken. This isn't so of the new critical edge that's
split during this process. If it turns out that the destination block has only
one predecessor, and that being a BB with an indirect branch, then it won't be
marked as 'used' and may be removed.
PR10072

llvm-svn: 132638
2011-06-04 09:42:04 +00:00
Frits van Bommel
ad964559ef Add a parameter to ConstantFoldTerminator() that callers can use to ask it to also clean up the condition of any conditional terminator it folds to be unconditional, if that turns the condition into dead code. This just means it calls RecursivelyDeleteTriviallyDeadInstructions() in strategic spots. It defaults to the old behavior.
I also changed -simplifycfg, -jump-threading and -codegenprepare to use this to produce slightly better code without any extra cleanup passes (AFAICT this was the only place in -simplifycfg where now-dead conditions of replaced terminators weren't being cleaned up). The only other user of this function is -sccp, but I didn't read that thoroughly enough to figure out whether it might be holding pointers to instructions that could be deleted by this.

llvm-svn: 131855
2011-05-22 16:24:18 +00:00
Devang Patel
1407fb4bbe Reapply r131605. This time with a fix, which is to use NoFolder.
llvm-svn: 131673
2011-05-19 20:52:46 +00:00
Rafael Espindola
964602d7ba revert 131605 to fix PR9946.
llvm-svn: 131620
2011-05-19 02:26:30 +00:00
Devang Patel
3015a54813 Use IRBuilder.
llvm-svn: 131609
2011-05-19 00:13:33 +00:00
Devang Patel
31458a0002 Use IRBuilder while simplifying unreachable.
llvm-svn: 131607
2011-05-19 00:09:21 +00:00
Devang Patel
4b13f39b77 Use IRBuilder while simplifying conditional branch.
llvm-svn: 131605
2011-05-18 23:59:51 +00:00
Devang Patel
7de6c4bf75 Use IRBuilder while simplifying branch.
llvm-svn: 131598
2011-05-18 23:18:47 +00:00
Devang Patel
dd14e0f7fa Use IRBuilder while simplifying return instruction.
llvm-svn: 131580
2011-05-18 21:33:11 +00:00
Devang Patel
583805530c Spread use of IRBuilder even more.
llvm-svn: 131571
2011-05-18 20:53:17 +00:00
Devang Patel
a7ec47d23c Use IRBuilder while simplifying switch instruction.
llvm-svn: 131566
2011-05-18 20:35:38 +00:00
Devang Patel
0b373dca1f Use IRBuilder while simplifying unwind.
llvm-svn: 131561
2011-05-18 20:01:18 +00:00
Devang Patel
2c2ea226b7 Use IRBuilder while simplifying terminator.
llvm-svn: 131552
2011-05-18 18:43:31 +00:00
Devang Patel
767f6930bc Use IRBuilder while simplifying unconditional branch.
llvm-svn: 131551
2011-05-18 18:28:48 +00:00
Devang Patel
5c810ce4a3 Use IRBuilder while folding two entry PHINode.
llvm-svn: 131548
2011-05-18 18:16:44 +00:00
Devang Patel
15ad6761da Set up IRBuilder for use during simplification.
llvm-svn: 131545
2011-05-18 18:01:27 +00:00
Devang Patel
b849cd511b Preseve line numbers while simplifying CFG.
llvm-svn: 131508
2011-05-17 23:29:05 +00:00
Benjamin Kramer
d96205c4e5 SimplifyCFG: Use ComputeMaskedBits to prune dead cases from switch instructions.
llvm-svn: 131345
2011-05-14 15:57:25 +00:00
Peter Collingbourne
616044acd5 SimplifyCFG: Expose phi node folding cost threshold as command line parameter
llvm-svn: 130528
2011-04-29 18:47:38 +00:00
Peter Collingbourne
e3511e15e0 SimplifyCFG: Add CostRemaining parameter to DominatesMergePoint
llvm-svn: 130527
2011-04-29 18:47:31 +00:00
Peter Collingbourne
61f6602acd SimplifyCFG: Add Trunc, ZExt and SExt to the list of cheap instructions for phi node folding
llvm-svn: 130526
2011-04-29 18:47:25 +00:00
Chris Lattner
fba5cdfce1 rework FoldBranchToCommonDest to exit earlier when there is a bonus
instruction around, reducing work.

Greatly simplify handling of debug instructions.  There is no need to
build up a vector of them and then move them into the one predecessor
if we're processing a block.  Instead just rescan the block and *copy*
them into the pred.  If a block gets merged into multiple preds, this
will retain more debug info.

llvm-svn: 129502
2011-04-14 02:44:53 +00:00
Chris Lattner
7d4cdae564 comment cleanup, use moveBefore instead of removeFromParent+insertBefore.
llvm-svn: 129319
2011-04-11 23:24:57 +00:00
Devang Patel
bc3d8b212f Do not let debug info interfer with branch folding.
llvm-svn: 129114
2011-04-07 23:11:25 +00:00
Devang Patel
197c35298a While hoisting common code from if/else, hoist debug info intrinsics if they match.
llvm-svn: 129078
2011-04-07 17:27:36 +00:00
Devang Patel
e48ddf863b Simplify. isIdenticalToWhenDefined() checks opcode.
llvm-svn: 129041
2011-04-07 00:30:15 +00:00
Devang Patel
d715ec82b4 While folding branch to a common destination into a predecessor, copy dbg values also.
llvm-svn: 129035
2011-04-06 22:37:20 +00:00
Jay Foad
52131344a2 Remove PHINode::reserveOperandSpace(). Instead, add a parameter to
PHINode::Create() giving the (known or expected) number of operands.

llvm-svn: 128537
2011-03-30 11:28:46 +00:00
Jay Foad
e0938d8a87 (Almost) always call reserveOperandSpace() on newly created PHINodes.
llvm-svn: 128535
2011-03-30 11:19:20 +00:00
Eli Friedman
c4414c6e92 PR9450: Make switch optimization in SimplifyCFG not dependent on the ordering
of pointers in an std::map.

llvm-svn: 127650
2011-03-15 02:23:35 +00:00
Eli Friedman
aac35b3fbb PR9420; an instruction before an unreachable is guaranteed not to have any
reachable uses, but there still might be uses in dead blocks.  Use the
standard solution of replacing all the uses with undef.  This is
a rare case because it's very sensitive to phase ordering in SimplifyCFG.

llvm-svn: 127299
2011-03-09 00:48:33 +00:00
Frits van Bommel
8ae07996c9 Teach SimplifyCFG that (switch (select cond, X, Y)) is better expressed as a branch.
Based on a patch by Alistair Lynn.

llvm-svn: 126647
2011-02-28 09:44:07 +00:00
Benjamin Kramer
ceb5daa567 Revert "SimplifyCFG: GEPs with just one non-constant index are also cheap."
Yes, there are other types than i8* and GEPs on them can produce an add+multiply.
We don't consider that cheap enough to be speculatively executed.

llvm-svn: 126481
2011-02-25 10:33:33 +00:00
Benjamin Kramer
dfdca1a14d SimplifyCFG: GEPs with just one non-constant index are also cheap.
llvm-svn: 126452
2011-02-24 23:26:09 +00:00
Benjamin Kramer
27361a7124 SimplifyCFG: GEPs with constant indices are cheap enough to be executed unconditionally.
llvm-svn: 126445
2011-02-24 22:46:11 +00:00
Benjamin Kramer
8d6a8c130b SimplifyCFG: Track the number of used icmps when turning a icmp chain into a switch. If we used only one icmp, don't turn it into a switch.
Also prevent the switch-to-icmp transform from creating identity adds, noticed by Marius Wachtler.

llvm-svn: 125056
2011-02-07 22:37:28 +00:00
Benjamin Kramer
62aa46b852 SimplifyCFG: Also transform switches that represent a range comparison but are not sorted into sub+icmp.
This transforms another 1000 switches in gcc.c.

llvm-svn: 124826
2011-02-03 22:51:41 +00:00
Benjamin Kramer
f4ea1d5f79 SimplifyCFG: Turn switches into sub+icmp+branch if possible.
This makes the job of the later optzn passes easier, allowing the vast amount of
icmp transforms to chew on it.

We transform 840 switches in gcc.c, leading to a 16k byte shrink of the resulting
binary on i386-linux.

The testcase from README.txt now compiles into
  decl  %edi
  cmpl  $3, %edi
  sbbl  %eax, %eax
  andl  $1, %eax
  ret

llvm-svn: 124724
2011-02-02 15:56:22 +00:00
Evan Cheng
d983eba7dc Re-apply r124518 with fix. Watch out for invalidated iterator.
llvm-svn: 124526
2011-01-29 04:46:23 +00:00
Evan Cheng
65b8ccf6ac Revert r124518. It broke Linux self-host.
llvm-svn: 124522
2011-01-29 02:43:04 +00:00
Evan Cheng
d4eff31476 Re-commit r124462 with fixes. Tail recursion elim will now dup ret into unconditional predecessor to enable TCE on demand.
llvm-svn: 124518
2011-01-29 01:29:26 +00:00
Evan Cheng
aaa9606b2f Revert r124462. There are a few big regressions that I need to fix first.
llvm-svn: 124478
2011-01-28 07:12:38 +00:00
Evan Cheng
417fca86c4 - Stop simplifycfg from duplicating "ret" instructions into unconditional
branches. PR8575, rdar://5134905, rdar://8911460.
- Allow codegen tail duplication to dup small return blocks after register
  allocation is done.

llvm-svn: 124462
2011-01-28 02:19:21 +00:00
Frits van Bommel
8e158495f1 Factor the actual simplification out of SimplifyIndirectBrOnSelect and into a new helper function so it can be reused in e.g. an upcoming SimplifySwitchOnSelect.
No functional change.

llvm-svn: 123234
2011-01-11 12:52:11 +00:00
Chris Lattner
6b8b4855ff simplify this a bit.
llvm-svn: 122156
2010-12-18 20:22:49 +00:00
Benjamin Kramer
e5f49c4ff2 SimplifyCFG: Ranges can be larger than 64 bits. Fixes Release-selfhost build.
llvm-svn: 122054
2010-12-17 10:48:14 +00:00
Chris Lattner
d14b0f1db7 improve switch formation to handle small range
comparisons formed by comparisons.  For example,
this:

void foo(unsigned x) {
  if (x == 0 || x == 1 || x == 3 || x == 4 || x == 6) 
    bar();
}

compiles into:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$6, %edi
	ja	LBB0_2
## BB#1:                                ## %entry
	movl	%edi, %eax
	movl	$91, %ecx
	btq	%rax, %rcx
	jb	LBB0_3

instead of:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	cmpl	$2, %edi
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	cmpl	$6, %edi
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movl	%edi, %eax
	movl	$88, %ecx
	btq	%rax, %rcx
	jb	LBB0_4

This catches a bunch of cases in GCC, which look like this:

 %804 = load i32* @which_alternative, align 4, !tbaa !0
 %805 = icmp ult i32 %804, 2
 %806 = icmp eq i32 %804, 3
 %or.cond121 = or i1 %805, %806
 %807 = icmp eq i32 %804, 4
 %or.cond124 = or i1 %or.cond121, %807
 br i1 %or.cond124, label %.thread, label %808

turning this into a range comparison.

llvm-svn: 122045
2010-12-17 06:20:15 +00:00
Chris Lattner
e893e2601e make qsort predicate more conformant by returning 0 for equal values.
llvm-svn: 121838
2010-12-15 04:52:41 +00:00
Chris Lattner
7499b452c1 - Insert new instructions before DomBlock's terminator,
which is simpler than finding a place to insert in BB.
 - Don't perform the 'if condition hoisting' xform on certain
   i1 PHIs, as it interferes with switch formation.

This re-fixes "example 7", without breaking the world hopefully.

llvm-svn: 121764
2010-12-14 08:46:09 +00:00
Chris Lattner
335f0e4ad4 fix two significant issues with FoldTwoEntryPHINode:
first, it can kick in on blocks whose conditions have been
folded to a constant, even though one of the edges will be
trivially folded.

second, it doesn't clean up the "if diamond" that it just 
eliminated away.  This is a problem because other simplifycfg
xforms kick in depending on the order of block visitation,
causing pointless work.

llvm-svn: 121762
2010-12-14 08:01:53 +00:00
Chris Lattner
dc20a7d38c remove the instsimplify logic I added in r121754. It is apparently
breaking the selfhost builds, though I can't fathom how.

llvm-svn: 121761
2010-12-14 07:53:03 +00:00
Chris Lattner
9ac168d0ab clean up logic, convert std::set to SmallPtrSet, handle the case
when all 2-entry phis are simplified away.

llvm-svn: 121760
2010-12-14 07:41:39 +00:00
Chris Lattner
9fd838d31b tidy up a bit, move DEBUG down to when we commit to doing the transform so we
don't print it unless the xform happens.

llvm-svn: 121758
2010-12-14 07:23:10 +00:00
Chris Lattner
b42d293faa use SimplifyInstruction instead of reimplementing part of it.
llvm-svn: 121757
2010-12-14 07:20:29 +00:00
Chris Lattner
fb73de482c simplify GetIfCondition by using getSinglePredecessor.
llvm-svn: 121756
2010-12-14 07:15:21 +00:00
Chris Lattner
0f4d67bd88 use AddPredecessorToBlock in 3 places instead of a manual loop.
llvm-svn: 121755
2010-12-14 07:09:42 +00:00
Chris Lattner
a07cc6f4fd make FoldTwoEntryPHINode use instsimplify a bit, make
GetIfCondition faster by avoiding pred_iterator.  No
really interesting change.

llvm-svn: 121754
2010-12-14 07:00:00 +00:00
Chris Lattner
d7beca3782 improve DEBUG's a bit, switch to eraseFromParent() to simplify
code a bit, switch from constant folding to instsimplify.

llvm-svn: 121751
2010-12-14 06:17:25 +00:00
Chris Lattner
5a9d59d918 reapply my recent change that disables a piece of the switch formation
work, but fixes 400.perlbmk.

llvm-svn: 121749
2010-12-14 05:57:30 +00:00
Owen Anderson
3e5648896e Fix recent buildbot breakage by pulling SimplifyCFG back to its state as of r121694, the most recent state
where I'm confident there were no crashes or miscompilations.  XFAIL the test added since then for now.

llvm-svn: 121733
2010-12-13 23:49:28 +00:00
Chris Lattner
a6e5d5694a temporarily disable part of my previous patch, which causes an iterator invalidation issue, causing a crash on some versions of perlbmk.
llvm-svn: 121728
2010-12-13 23:02:19 +00:00
Chris Lattner
2d434e594e add some DEBUG's.
llvm-svn: 121711
2010-12-13 19:55:30 +00:00
Benjamin Kramer
1e155ab7e1 Fix sort predicate. qsort(3)'s predicate semantics differ from std::sort's. Fixes PR 8780.
llvm-svn: 121705
2010-12-13 18:20:38 +00:00
Chris Lattner
fb836f8c1a reinstate my patch: the miscompile was caused by an inverted branch in the
'and' case.

llvm-svn: 121695
2010-12-13 08:12:19 +00:00
Chris Lattner
79db357d80 Completely disable the optimization I added in r121680 until
I can track down a miscompile.  This should bring the buildbots
back to life

llvm-svn: 121693
2010-12-13 07:41:29 +00:00
Chris Lattner
fbeb55844b Make simplifycfg reprocess newly formed "br (cond1 | cond2)" conditions
when simplifying, allowing them to be eagerly turned into switches.  This
is the last step required to get "Example 7" from this blog post:
http://blog.regehr.org/archives/320

On X86, we now generate this machine code, which (to my eye) seems better
than the ICC generated code:

_crud:                                  ## @crud
## BB#0:                                ## %entry
	cmpb	$33, %dil
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	addb	$-34, %dil
	cmpb	$58, %dil
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movzbl	%dil, %eax
	movabsq	$288230376537592865, %rcx ## imm = 0x400000017001421
	btq	%rax, %rcx
	jb	LBB0_4
LBB0_3:                                 ## %lor.rhs
	xorl	%eax, %eax
	ret
LBB0_4:                                 ## %lor.end
	movl	$1, %eax
	ret

llvm-svn: 121690
2010-12-13 07:00:06 +00:00
Chris Lattner
1d05761df4 make this logic a bit simpler.
llvm-svn: 121689
2010-12-13 06:36:51 +00:00
Chris Lattner
25c3af35d8 split all the guts of SimplifyCFGOpt::run out into one function
per terminator kind.

llvm-svn: 121688
2010-12-13 06:25:44 +00:00
Chris Lattner
cb570f87e5 fix a bug in r121680 that upset the various buildbots.
llvm-svn: 121687
2010-12-13 05:34:18 +00:00
Chris Lattner
a6db741f3d refactor the speculative execution logic to be factored into the cond branch code instead of
doing a cfg search for every block simplified.

llvm-svn: 121686
2010-12-13 05:26:52 +00:00
Chris Lattner
466f54ffcf simplify a bunch of code.
llvm-svn: 121685
2010-12-13 05:20:28 +00:00
Chris Lattner
6df7bdd810 move HoistThenElseCodeToIf up to a more logical and efficient-to-handle place.
llvm-svn: 121684
2010-12-13 05:15:29 +00:00
Chris Lattner
2e3832d9a0 move 'MergeBlocksIntoPredecessor' call earlier. Use
getSinglePredecessor to simplify code.

llvm-svn: 121683
2010-12-13 05:10:48 +00:00
Chris Lattner
a69c443459 factor new code out to a SimplifyBranchOnICmpChain helper function.
llvm-svn: 121681
2010-12-13 05:03:41 +00:00
Chris Lattner
a442f24a36 enhance the "change or icmp's into switch" xform to handle one value in an
'or sequence' that it doesn't understand.  This allows us to optimize
something insane like this:

int crud (unsigned char c, unsigned x)
 {
   if(((((((((( (int) c <= 32 ||
                    (int) c == 46) || (int) c == 44)
                  || (int) c == 58) || (int) c == 59) || (int) c == 60)
               || (int) c == 62) || (int) c == 34) || (int) c == 92)
            || (int) c == 39) != 0)
     foo();
 }

into:

define i32 @crud(i8 zeroext %c, i32 %x) nounwind ssp noredzone {
entry:
  %cmp = icmp ult i8 %c, 33
  br i1 %cmp, label %if.then, label %switch.early.test

switch.early.test:                                ; preds = %entry
  switch i8 %c, label %if.end [
    i8 39, label %if.then
    i8 44, label %if.then
    i8 58, label %if.then
    i8 59, label %if.then
    i8 60, label %if.then
    i8 62, label %if.then
    i8 46, label %if.then
    i8 92, label %if.then
    i8 34, label %if.then
  ]

by pulling the < comparison out ahead of the newly formed switch.

llvm-svn: 121680
2010-12-13 04:50:38 +00:00
Chris Lattner
5a177e681e merge two very similar functions into one that has a bool argument.
llvm-svn: 121678
2010-12-13 04:26:26 +00:00
Chris Lattner
9b1af510cb don't bother handling non-canonical icmp's
llvm-svn: 121676
2010-12-13 04:18:32 +00:00
Chris Lattner
395252d93e inline a function, making the result much simpler.
llvm-svn: 121675
2010-12-13 04:15:19 +00:00
Chris Lattner
62cc76e9cc Fix my previous patch to handle a degenerate case that the llvm-gcc
bootstrap buildbot tripped over.

llvm-svn: 121674
2010-12-13 03:43:57 +00:00