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Gerolf Hoflehner 2432bd0ddd [SimplifyCFG] Fix for "endless" loop after dead code removal (Alternative to 
D16251)

Summary:
This is a simpler fix to the problem than the dominator approach in
http://reviews.llvm.org/D16251. It adds only values into the gather() while loop
that have been seen before.

The actual endless loop is in the constant compare gather() routine in
Utils/SimplifyCFG.cpp. The same value ret.0.off0.i is pushed back into the
queue:
%.ret.0.off0.i = or i1 %.ret.0.off0.i, %cmp10.i

Here is what happens at the IR level:

for.cond.i:                                       ; preds = %if.end6.i,
%if.end.i54
%ix.0.i = phi i32 [ 0, %if.end.i54 ], [ %inc.i55, %if.end6.i ]
%ret.0.off0.i = phi i1 [false, %if.end.i54], [%.ret.0.off0.i, %if.end6.i] <<<
%cmp2.i = icmp ult i32 %ix.0.i, %11
br i1 %cmp2.i, label %for.body.i, label %LBJ_TmpSimpleNeedExt.exit

if.end6.i:                                        ; preds = %for.body.i
%cmp10.i = icmp ugt i32 %conv.i, %add9.i
%.ret.0.off0.i = or i1 %ret.0.off0.i, %cmp10.i <<<

When if.end.i54 gets eliminated which removes the definition of ret.0.off0.i.
The result is the expression %.ret.0.off0.i = or i1 %.ret.0.off0.i, %cmp10.i
(Note the first ‘or’ operand is now %.ret.0.off0.i, and *NOT* %ret.0.off0.i).
And
now there is use of .ret.0.off0.i before a definition which triggers the
“endless” loop in gather():

while(!DFT.empty()) {

    V = DFT.pop_back_val();   // V is .ret.0.off0.i

    if (Instruction *I = dyn_cast<Instruction>(V)) {
      // If it is a || (or && depending on isEQ), process the operands.
      if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
        DFT.push_back(I->getOperand(1));  // This is now .ret.0.off0.i also
        DFT.push_back(I->getOperand(0));

        continue; // “endless loop” for .ret.0.off0.i
      }

Reviewers: reames, ahatanak

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D16839

llvm-svn: 259730
 		2016-02-03 23:54:25 +00:00
..
ADCE [PM] Port ADCE to the new pass manager 2015-10-30 23:13:18 +00:00
AddDiscriminators Reimplement discriminator assignment algorithm. 2015-11-19 19:53:05 +00:00
AlignmentFromAssumptions Revert "Change memcpy/memset/memmove to have dest and source alignments." 2015-11-19 05:56:52 +00:00
ArgumentPromotion DI: Reverse direction of subprogram -> function edge. 2015-11-05 22:03:56 +00:00
AtomicExpand [IR] Add support for floating pointer atomic loads and stores 2015-12-16 00:49:36 +00:00
BBVectorize Have a single way for creating unique value names. 2015-11-22 00:16:24 +00:00
BDCE Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
BranchFolding Move branch folding test to a better location. 2015-12-03 19:41:25 +00:00
CodeExtractor Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
CodeGenPrepare [InstCombine] Rewrite bswap/bitreverse handling completely. 2016-01-15 09:20:19 +00:00
ConstProp IR: Make ConstantDataArray::getFP actually return a ConstantDataArray 2015-12-09 21:21:07 +00:00
ConstantHoisting
…
ConstantMerge [opaque pointer type] Add textual IR support for explicit type parameter for global aliases 2015-09-11 03:22:04 +00:00
CorrelatedValuePropagation [LVI] Introduce an intersect operation on lattice values 2016-02-02 03:15:40 +00:00
CrossDSOCFI [cfi] Cross-DSO CFI diagnostic mode (LLVM part). 2016-01-25 23:35:03 +00:00
DeadArgElim [OperandBundles] Have DeadArgElim play nice with operand bundles 2015-12-23 09:58:36 +00:00
DeadStoreElimination [BasicAliasAnalysis] Take into account operand bundles in the getModRefInfo function 2016-01-16 12:15:53 +00:00
EarlyCSE Fix several accidental DOS line endings in source files 2016-01-03 17:22:03 +00:00
EliminateAvailableExternally Don't change the visibility when converting a definition to a declaration. 2015-07-13 14:18:22 +00:00
Float2Int [Float2Int] Don't operate on vector instructions 2015-12-09 21:08:18 +00:00
ForcedFunctionAttrs [attrs] Split off the forced attributes utility into its own pass that 2015-12-27 08:13:45 +00:00
FunctionAttrs [attrs] Split the late-revisit pattern for deducing norecurse in 2016-01-08 10:55:52 +00:00
FunctionImport Fix bot failure from r257493: remove extraneous temp file read 2016-01-12 17:53:59 +00:00
GCOVProfiling [GCOV] Avoid emitting profile arcs for module and skeleton CUs 2016-01-21 17:04:42 +00:00
GVN Fix for two constant propagation problems in GVN with the assume intrinsic 2016-01-21 21:32:35 +00:00
GlobalDCE [opaque pointer type] Add textual IR support for explicit type parameter for global aliases 2015-09-11 03:22:04 +00:00
GlobalOpt Make sure that any new and optimized objects created during GlobalOPT copy all the attributes from the base object. 2016-01-22 21:18:20 +00:00
IPConstantProp [SCCP] Don't violate the lattice invariants 2016-01-07 21:36:16 +00:00
IRCE Revert r259662, which caused regressions on polly tests. 2016-02-03 18:05:57 +00:00
IndVarSimplify Revert r259662, which caused regressions on polly tests. 2016-02-03 18:05:57 +00:00
InferFunctionAttrs [BasicAA] Remove special casing of memset_pattern16 in favor of generic attribute inference 2016-01-06 04:53:16 +00:00
Inline Avoid inlining call sites in unreachable-terminated block 2016-02-01 20:55:11 +00:00
InstCombine [InstCombine] Revert r238452: Fold IntToPtr and PtrToInt into preceding loads. 2016-02-03 18:04:13 +00:00
InstMerge
…
InstSimplify [InstCombine] Simplify (x >> y) <= x 2016-01-21 18:55:54 +00:00
Internalize [opaque pointer type] Add textual IR support for explicit type parameter for global aliases 2015-09-11 03:22:04 +00:00
JumpThreading [LVI] Introduce an intersect operation on lattice values 2016-02-02 03:15:40 +00:00
LCSSA [WinEH] Update LCSSA to handle catchswitch with handlers inside and outside a loop 2015-12-18 18:12:35 +00:00
LICM [LICM] Keep metadata on control equivalent hoists 2016-01-28 15:51:58 +00:00
LoadCombine
…
LoopDeletion
…
LoopDistribute Allow LLE/LD and the loop versioning infrastructure to use SCEV predicates 2015-11-09 13:26:09 +00:00
LoopIdiom [LIR] Add support for structs and hand unrolled loops 2016-01-26 02:27:47 +00:00
LoopInterchange
…
LoopLoadElim Allow LLE/LD and the loop versioning infrastructure to use SCEV predicates 2015-11-09 13:26:09 +00:00
LoopReroll Enable loopreroll to rerool loop with pointer induction variable. 2016-01-25 19:43:45 +00:00
LoopRotate DI: Reverse direction of subprogram -> function edge. 2015-11-05 22:03:56 +00:00
LoopSimplify DI: Reverse direction of subprogram -> function edge. 2015-11-05 22:03:56 +00:00
LoopSimplifyCFG Add LoopSimplifyCFG pass 2016-01-29 22:35:36 +00:00
LoopStrengthReduce [LoopStrengthReduce] Don't rewrite PHIs with incoming values from CatchSwitches 2016-02-03 21:30:34 +00:00
LoopUnroll LoopUnroll: Use the optsize threshold for minsize as well 2016-01-11 22:39:43 +00:00
LoopUnswitch [IR] Reformulate LLVM's EH funclet IR 2015-12-12 05:38:55 +00:00
LoopVectorize [DemandedBits] Revert r249687 due to PR26071 2016-02-03 15:05:06 +00:00
LoopVersioning [LoopVersioning] Expose loop versioning as a pass too 2016-02-03 00:06:10 +00:00
LowerAtomic
…
LowerBitSets [cfi] Fix LowerBitSets on 32-bit targets. 2015-12-21 22:14:04 +00:00
LowerExpectIntrinsic [PM] Port StripDeadPrototypes to the new pass manager 2015-10-30 23:28:12 +00:00
LowerInvoke Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
LowerSwitch Have a single way for creating unique value names. 2015-11-22 00:16:24 +00:00
Mem2Reg [Mem2Reg] Respect optnone 2015-12-11 13:36:59 +00:00
MemCpyOpt Fix PR26051: Memcpy optimization should introduce a call to memcpy before the store destination position 2016-01-06 23:50:22 +00:00
MergeFunc [IR] Remove terminatepad 2015-12-14 18:34:23 +00:00
MetaRenamer Revert "Change memcpy/memset/memmove to have dest and source alignments." 2015-11-19 05:56:52 +00:00
NaryReassociate [NaryReassociate] allow candidate to have a different type 2015-12-18 21:36:30 +00:00
ObjCARC Add support for objc_unsafeClaimAutoreleasedReturnValue to the 2016-01-27 19:05:08 +00:00
PGOProfile [PGO] IR level instrumentation of indirect call value profiling 2016-01-21 18:11:44 +00:00
PartiallyInlineLibCalls
…
PhaseOrdering Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
PlaceSafepoints [PlaceSafepoints] Clamp NoStatepoints to true 2016-01-28 21:51:14 +00:00
PruneEH [PruneEH] Don't try to insert a terminator after another terminator 2016-01-23 06:00:44 +00:00
Reassociate Reassociate: Reprocess RedoInsts after each inst 2016-01-26 18:42:36 +00:00
Reg2Mem Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
RewriteStatepointsForGC [RS4GC] Remove unnecessary redirections from tests; NFC 2016-01-29 16:32:30 +00:00
SCCP [opaque pointer type] Add textual IR support for explicit type parameter for global aliases 2015-09-11 03:22:04 +00:00
SLPVectorizer Add test case missing from r259357 (NFC) 2016-02-01 19:09:24 +00:00
SROA [SROA] Also insert a bit piece expression if only one piece is needed 2016-01-14 20:06:34 +00:00
SafeStack [safestack] Make sure the unsafe stack pointer is popped in all cases 2016-02-02 01:03:11 +00:00
SampleProfile SamplePGO - Add initial support for inliner annotations. 2015-11-27 23:14:51 +00:00
ScalarRepl Revert "Change memcpy/memset/memmove to have dest and source alignments." 2015-11-19 05:56:52 +00:00
Scalarizer DI: Reverse direction of subprogram -> function edge. 2015-11-05 22:03:56 +00:00
SeparateConstOffsetFromGEP [SeparateConstOffsetFromGEP] sext(a)+sext(b) => sext(a+b) when a+b can't sign-overflow. 2015-08-14 02:02:05 +00:00
SimplifyCFG [SimplifyCFG] Fix for "endless" loop after dead code removal (Alternative to 2016-02-03 23:54:25 +00:00
Sink [IR] Reformulate LLVM's EH funclet IR 2015-12-12 05:38:55 +00:00
SpeculativeExecution
…
StraightLineStrengthReduce [SeparateConstOffsetFromGEP] strengthen the inbounds attribute 2015-08-13 18:48:49 +00:00
StripDeadPrototypes [PM] Port StripDeadPrototypes to the new pass manager 2015-10-30 23:28:12 +00:00
StripSymbols DI: Reverse direction of subprogram -> function edge. 2015-11-05 22:03:56 +00:00
StructurizeCFG AMDGPU: Replace some deprecated intrinsic uses in tests 2016-01-23 05:42:49 +00:00
TailCallElim Push isDereferenceableAndAlignedPointer down into isSafeToLoadUnconditionally 2016-01-17 12:35:29 +00:00
TailDup
…
Util This patch adds MemorySSA to LLVM. 2016-02-02 22:46:49 +00:00