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llvm-project/llvm/test/Transforms/SimplifyCFG
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Chuang-Yu Cheng dbe00d51b4 SimplifyCFG is able to detect the pattern: 
(i == 5334 || i == 5335)
to:
    ((i & -2) == 5334)

This transformation has some incorrect side conditions. Specifically, the
transformation is only applied when the right-hand side constant (5334 in
the example) is a power of two not equal and not equal to the negated mask.
These side conditions were added in r258904 to fix PR26323. The correct side
condition is that: ((Constant & Mask) == Constant)[(5334 & -2) == 5334].

It's a little bit hard to see why these transformations are correct and what
the side conditions ought to be. Here is a CVC3 program to verify them for
64-bit values:
    ONE  : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63);
    x    : BITVECTOR(64);
    y    : BITVECTOR(64);
    z    : BITVECTOR(64);
    mask : BITVECTOR(64) = BVSHL(ONE, z);
    QUERY( (y & ~mask = y) =>
           ((x & ~mask = y) <=> (x = y OR x = (y |  mask)))
    );

Please note that each pattern must be a dual implication (<--> or iff). One
directional implication can create spurious matches. If the implication is
only one-way, an unsatisfiable condition on the left side can imply a
satisfiable condition on the right side. Dual implication ensures that
satisfiable conditions are transformed to other satisfiable conditions and
unsatisfiable conditions are transformed to other unsatisfiable conditions.

Here is a concrete example of a unsatisfiable condition on the left
implying a satisfiable condition on the right:
    mask = (1 << z)
    (x & ~mask) == y --> (x == y || x == (y | mask))

Substituting y = 3, z = 0 yields:
    (x & -2) == 3 --> (x == 3 || x == 2)

The version of this code before r258904 had no side-conditions and
incorrectly justified itself in comments through one-directional
implication.

Thanks to Chandler for the suggestion!

Author: Thomas Jablin (tjablin)
Reviewers: chandlerc majnemer hfinkel cycheng

http://reviews.llvm.org/D21417

llvm-svn: 272873
 		2016-06-16 04:44:25 +00:00
..
AArch64 [AArch64] add overrides for isCheapToSpeculateCttz() and isCheapToSpeculateCtlz() 2015-11-10 18:11:37 +00:00
AMDGPU AMDGPU: Fix some places missed in rename 2015-06-19 17:39:03 +00:00
ARM [ARM] add overrides for isCheapToSpeculateCttz() and isCheapToSpeculateCtlz() 2015-11-10 19:24:31 +00:00
Mips [MIPS] add overrides for isCheapToSpeculateCttz() and isCheapToSpeculateCtlz() 2015-11-11 17:24:56 +00:00
PowerPC [CodeGenPrepare] Removed duplicate logic. SimplifyCFG already knows how to speculate calls to cttz/ctlz. 2015-02-13 14:15:48 +00:00
SPARC
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X86 [SimlifyCFG] Prevent passes from destroying canonical loop structure, especially for nested loops 2016-03-29 04:08:57 +00:00
2002-05-21-PHIElimination.ll
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2002-09-24-PHIAssertion.ll
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2003-03-07-DominateProblem.ll
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2003-08-05-InvokeCrash.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
2003-08-17-BranchFold.ll
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2003-08-17-BranchFoldOrdering.ll
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2003-08-17-FoldSwitch-dbg.ll [opaque pointer type] Add textual IR support for explicit type parameter to gep operator 2015-03-13 18:20:45 +00:00
2003-08-17-FoldSwitch.ll regenerate checks 2016-03-28 22:12:21 +00:00
2004-12-10-SimplifyCFGCrash.ll
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2005-06-16-PHICrash.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2005-08-01-PHIUpdateFail.ll [opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction 2015-02-27 19:29:02 +00:00
2005-10-02-InvokeSimplify.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
2005-12-03-IncorrectPHIFold.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2006-02-17-InfiniteUnroll.ll
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2006-06-12-InfLoop.ll
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2006-08-03-Crash.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2006-10-19-UncondDiv.ll
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2006-12-08-Ptr-ICmp-Branch.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2007-11-22-InvokeNoUnwind.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
2007-12-21-Crash.ll [opaque pointer type] Add textual IR support for explicit type parameter to the call instruction 2015-04-16 23:24:18 +00:00
2008-01-02-hoist-fp-add.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2008-05-16-PHIBlockMerge.ll [SimlifyCFG] Prevent passes from destroying canonical loop structure, especially for nested loops 2016-03-29 04:08:57 +00:00
2008-07-13-InfLoopMiscompile.ll remove the metadata added with r267827 2016-04-30 00:02:36 +00:00
2008-09-08-MultiplePred.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2008-09-17-SpeculativeHoist.ll
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2008-10-03-SpeculativelyExecuteBeforePHI.ll
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2008-12-06-SingleEntryPhi.ll
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2008-12-16-DCECond.ll [opaque pointer type] Add textual IR support for explicit type parameter to the call instruction 2015-04-16 23:24:18 +00:00
2009-01-18-PHIPropCrash.ll
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2009-01-19-UnconditionalTrappingConstantExpr.ll
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2009-05-12-externweak.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
2010-03-30-InvokeCrash.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
2011-03-08-UnreachableUse.ll
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2011-09-05-TrivialLPad.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
BrUnwind.ll
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CoveredLookupTable.ll
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DeadSetCC.ll
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EmptyBlockMerge.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
EqualPHIEdgeBlockMerge.ll [SimlifyCFG] Prevent passes from destroying canonical loop structure, especially for nested loops 2016-03-29 04:08:57 +00:00
ForwardSwitchConditionToPHI.ll
…
HoistCode.ll
…
InfLoop.ll [SimplifyCFG] Fix for "endless" loop after dead code removal (Alternative to 2016-02-03 23:54:25 +00:00
MagicPointer.ll [opaque pointer type] Add textual IR support for explicit type parameter to gep operator 2015-03-13 18:20:45 +00:00
PHINode.ll
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PR9946.ll
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PR16069.ll regenerate checks 2016-03-28 22:12:21 +00:00
PR17073.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
PR25267.ll [SimplifyCFG] Don't use-after-free an SSA value 2015-10-21 18:22:24 +00:00
PR27615-simplify-cond-br.ll [SimplifyCFG] isSafeToSpeculateStore now ignores debug info 2016-05-04 15:40:57 +00:00
PhiBlockMerge.ll regenerate checks 2016-03-28 22:12:21 +00:00
PhiBlockMerge2.ll
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PhiEliminate.ll
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PhiEliminate2.ll propagate 'unpredictable' metadata on select instructions 2016-03-17 15:30:52 +00:00
PhiEliminate3.ll
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PhiNoEliminate.ll
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SpeculativeExec.ll Revert "Revert "Strip metadata when speculatively hoisting instructions (r252604)" 2015-11-18 14:50:18 +00:00
UncondBranchToReturn.ll
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UnreachableEliminate.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
assume.ll
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attr-convergent.ll [SimplifyCFG] Don't fold conditional branches that contain calls to convergent functions. 2016-02-12 21:01:36 +00:00
attr-noduplicate.ll [opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction 2015-02-27 19:29:02 +00:00
basictest.ll [SimplifyCFG] Prefer a simplification based on a dominating condition. 2016-05-06 14:25:14 +00:00
branch-cond-merge.ll
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branch-cond-prop.ll
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branch-fold-dbg.ll [PR27284] Reverse the ownership between DICompileUnit and DISubprogram. 2016-04-15 15:57:41 +00:00
branch-fold-test.ll
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branch-fold-threshold.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
branch-fold.ll
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branch-phi-thread.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
bug-25299.ll [SimplifyCFG] Extend SimplifyResume to handle phi of trivial landing pad. 2016-01-10 05:48:01 +00:00
clamp.ll [SimplifyCFG] Add test for r229099 2015-02-13 11:08:40 +00:00
combine-parallel-mem-md.ll [SimplifyCFG] Preserve !llvm.mem.parallel_loop_access when merging 2016-04-26 02:06:06 +00:00
common-dest-folding.ll [opaque pointer type] Add textual IR support for explicit type parameter to the call instruction 2015-04-16 23:24:18 +00:00
dbginfo.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
dce-cond-after-folding-terminator.ll
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duplicate-landingpad.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
duplicate-phis.ll
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empty-catchpad.ll [WinEH] Simplify unreachable catchpads 2016-01-05 02:37:41 +00:00
empty-cleanuppad.ll [SimplifyCFG] Don't kill empty cleanuppads with multiple uses 2016-06-04 23:50:03 +00:00
extract-cost.ll
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guards.ll [SimplifyCFG] Fold `llvm.guard(false)` to unreachable 2016-04-21 05:09:12 +00:00
hoist-common-code.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
hoist-dbgvalue.ll [PR27284] Reverse the ownership between DICompileUnit and DISubprogram. 2016-04-15 15:57:41 +00:00
hoist-with-range.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
implied-cond-matching-false-dest.ll [ValueTracking] Improve isImpliedCondition when the dominating cond is false. 2016-04-25 17:23:36 +00:00
implied-cond-matching-imm.ll [ValueTracking] Improve isImpliedCondition for matching LHS and Imm RHSs. 2016-05-05 15:39:18 +00:00
implied-cond-matching.ll Fix typo from r267432. 2016-04-25 18:20:27 +00:00
implied-cond.ll [SimplifyCFG] Constant fold a branch implied by it's incoming edge 2015-10-29 03:11:49 +00:00
indirectbr.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
invoke.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
invoke_unwind.ll [SimplifyCFG] Extend SimplifyResume to handle phi of trivial landing pad. 2016-01-10 05:48:01 +00:00
iterative-simplify.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
lifetime.ll Revert "[SimplifyCFG] Extend TryToSimplifyUncondBranchFromEmptyBlock for empty block including lifetime intrinsics" 2016-05-02 19:43:22 +00:00
merge-cleanuppads.ll [SimplifyCFG] Merge together cleanuppads 2016-02-20 01:07:45 +00:00
merge-cond-stores-2.ll Tweak unnamed label syntax in textual IR for easier matching in tests. 2016-01-27 21:53:08 +00:00
merge-cond-stores.ll Revert "Don't create unnecessary PHIs" 2015-12-14 22:36:57 +00:00
multiple-phis.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
no_speculative_loads_with_asan.ll [asan] Disabling speculative loads under asan. Patch by Mike Aizatsky 2015-10-14 00:21:05 +00:00
no_speculative_loads_with_tsan.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
noreturn-call.ll
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phi-undef-loadstore.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
preserve-branchweights-partial.ll IR: Make metadata typeless in assembly 2014-12-15 19:07:53 +00:00
preserve-branchweights-switch-create.ll IR: Make metadata typeless in assembly 2014-12-15 19:07:53 +00:00
preserve-branchweights.ll Follow-up patch of http://reviews.llvm.org/D19948 to handle missing profiles when simplifying CFG. 2016-05-18 22:41:03 +00:00
preserve-load-metadata-2.ll Preserve load alignment and dereferenceable metadata during some transformations 2015-11-02 17:53:51 +00:00
preserve-load-metadata-3.ll Preserve load alignment and dereferenceable metadata during some transformations 2015-11-02 17:53:51 +00:00
preserve-load-metadata.ll Preserve load alignment and dereferenceable metadata during some transformations 2015-11-02 17:53:51 +00:00
preserve-make-implicit-on-switch-to-br.ll [ConstantFoldTerminator] Preserve make.implicit metadata when converting SwitchInst to BranchInst 2015-08-07 19:30:12 +00:00
return-merge.ll
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seh-nounwind.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
select-gep.ll [opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction 2015-02-27 19:29:02 +00:00
sink-common-code.ll [SimplifyCFG] Revise common code sinking 2014-12-23 08:26:55 +00:00
speculate-math.ll Revert "Revert "[SimplifyCFG] allow speculation of exactly one expensive instruction (PR24818)"" 2016-01-27 02:59:41 +00:00
speculate-store.ll [SimplifyCFG] propagate branch metadata when creating select (PR26636) 2016-03-26 23:30:50 +00:00
speculate-vector-ops.ll
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speculate-with-offset.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
statepoint-invoke-unwind.ll [gc.statepoint] Change gc.statepoint intrinsic's return type to token type instead of i32 type 2015-12-26 07:54:32 +00:00
switch-dead-default.ll [SimplifyCFG] Use known bits to eliminate dead switch defaults 2015-09-10 17:44:47 +00:00
switch-masked-bits.ll [SimplifyCFG] eliminate switch cases based on known range of switch condition 2016-05-20 14:53:09 +00:00
switch-on-const-select.ll
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switch-range-to-icmp.ll SimplifyCFG: don't remove unreachable default switch destinations 2015-01-26 19:52:32 +00:00
switch-simplify-crash.ll
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switch-to-br.ll Add some tests for SimplifyCFG's ConstantFoldTerminator(). NFC. 2014-12-04 22:19:25 +00:00
switch-to-icmp.ll
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switch-to-select-multiple-edge-per-block-phi.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
switch-to-select-two-case.ll SimplifyCFG: don't remove unreachable default switch destinations 2015-01-26 19:52:32 +00:00
switch_create.ll SimplifyCFG is able to detect the pattern: 2016-06-16 04:44:25 +00:00
switch_switch_fold.ll use FileCheck for tighter checking 2016-03-16 23:39:37 +00:00
switch_thread.ll reduce check strings; no need to check IR comments 2016-03-16 23:22:01 +00:00
trap-debugloc.ll [PR27284] Reverse the ownership between DICompileUnit and DISubprogram. 2016-04-15 15:57:41 +00:00
trapping-load-unreachable.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
two-entry-phi-return.ll [SimplifyCFG] propagate branch metadata when creating select (PR27344) 2016-04-15 15:32:12 +00:00
unreachable-blocks.ll [opaque pointer type] Add textual IR support for explicit type parameter to load instruction 2015-02-27 21:17:42 +00:00
unreachable-cleanuppad.ll [SimplifyCFG] Do not blindly remove unreachable blocks 2016-02-24 10:02:16 +00:00
volatile-phioper.ll [opaque pointer type] Add textual IR support for explicit type parameter to the call instruction 2015-04-16 23:24:18 +00:00
wineh-unreachable.ll [SimplifyCFG] Further improve our ability to remove redundant catchpads 2016-01-05 07:42:17 +00:00