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Roman Lebedev 6e2c5c8710 [InstSimplify] simplifyUnsignedRangeCheck(): if we know that X != 0, handle more cases (PR43246) 
Summary:
This is motivated by D67122 sanitizer check enhancement.
That patch seemingly worsens `-fsanitize=pointer-overflow`
overhead from 25% to 50%, which strongly implies missing folds.

In this particular case, given
```
char* test(char& base, unsigned long offset) {
  return &base + offset;
}
```
it will end up producing something like
https://godbolt.org/z/LK5-iH
which after optimizations reduces down to roughly
```
define i1 @t0(i8* nonnull %base, i64 %offset) {
  %base_int = ptrtoint i8* %base to i64
  %adjusted = add i64 %base_int, %offset
  %non_null_after_adjustment = icmp ne i64 %adjusted, 0
  %no_overflow_during_adjustment = icmp uge i64 %adjusted, %base_int
  %res = and i1 %non_null_after_adjustment, %no_overflow_during_adjustment
  ret i1 %res
}
```
Without D67122 there was no `%non_null_after_adjustment`,
and in this particular case we can get rid of the overhead:

Here we add some offset to a non-null pointer,
and check that the result does not overflow and is not a null pointer.
But since the base pointer is already non-null, and we check for overflow,
that overflow check will already catch the null pointer,
so the separate null check is redundant and can be dropped.

Alive proofs:
https://rise4fun.com/Alive/WRzq

There are more patterns of "unsigned-add-with-overflow", they are not handled here,
but this is the main pattern, that we currently consider canonical,
so it makes sense to handle it.

https://bugs.llvm.org/show_bug.cgi?id=43246

Reviewers: spatel, nikic, vsk

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits, reames

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67332

llvm-svn: 371349
 		2019-09-08 20:14:15 +00:00
..
AliasAnalysis.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
AliasAnalysisEvaluator.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
AliasAnalysisSummary.cpp Move CFLGraph and the AA summary code over to the new `CallBase` 2019-02-11 09:25:41 +00:00
AliasAnalysisSummary.h Move CFLGraph and the AA summary code over to the new `CallBase` 2019-02-11 09:25:41 +00:00
AliasSetTracker.cpp [LICM/MSSA] Add promotion to scalars by building an AliasSetTracker with MemorySSA. 2019-02-06 20:25:17 +00:00
Analysis.cpp [MustExec] Add a generic "must-be-executed-context" explorer 2019-08-23 15:17:27 +00:00
AssumptionCache.cpp AssumptionCache: remove old affected values after RAUW. 2019-08-16 09:34:27 +00:00
BasicAliasAnalysis.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
BlockFrequencyInfo.cpp Add optional arg to profile count getters to filter 2019-04-24 19:51:16 +00:00
BlockFrequencyInfoImpl.cpp Add optional arg to profile count getters to filter 2019-04-24 19:51:16 +00:00
BranchProbabilityInfo.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
CFG.cpp Recommit "[GVN] Preserve loop related analysis/canonical forms." 2019-07-31 09:27:54 +00:00
CFGPrinter.cpp Rename F_{None,Text,Append} to OF_{None,Text,Append}. NFC 2019-08-05 05:43:48 +00:00
CFLAndersAliasAnalysis.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
CFLGraph.h [CFLGraph] Add support for unary fneg instruction. 2019-06-06 19:21:23 +00:00
CFLSteensAliasAnalysis.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
CGSCCPassManager.cpp Revert "[CallGraph] Refine call graph for indirect calls with !callees metadata" 2019-08-16 10:59:18 +00:00
CMakeLists.txt Title: Loop Cache Analysis 2019-08-09 13:56:29 +00:00
CallGraph.cpp Revert "[CallGraph] Refine call graph for indirect calls with !callees metadata" 2019-08-16 10:59:18 +00:00
CallGraphSCCPass.cpp [CallSite removal] Move the legacy PM, call graph, and some inliner 2019-04-19 05:59:42 +00:00
CallPrinter.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
CaptureTracking.cpp [CaptureTracker] Let subclasses provide dereferenceability information 2019-08-19 21:56:38 +00:00
CmpInstAnalysis.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
CodeMetrics.cpp Remove `CallSite` from the CodeMetrics analysis, moving it to the new 2019-02-11 09:03:32 +00:00
ConstantFolding.cpp [ConstantFolding] Refactor functions not available before C99 (NFC) 2019-09-06 18:24:21 +00:00
CostModel.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
Delinearization.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
DemandedBits.cpp [DemandedBits] Remove some redundancy in the work list 2019-03-03 14:50:01 +00:00
DependenceAnalysis.cpp [llvm] Migrate llvm::make_unique to std::make_unique 2019-08-15 15:54:37 +00:00
DivergenceAnalysis.cpp [DivergenceAnalysis] Add methods for querying divergence at use 2019-07-29 10:22:09 +00:00
DomPrinter.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
DomTreeUpdater.cpp [DTU] Refine the interface and logic of applyUpdates 2019-02-22 13:48:38 +00:00
DominanceFrontier.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
EHPersonalities.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
GlobalsModRef.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
GuardUtils.cpp [WideableCond] Fix a nasty bug in detection of "explicit guards" 2019-04-02 16:51:43 +00:00
IVDescriptors.cpp Save the induction binary operator in IVDescriptors for non FP induction variables. 2019-05-14 13:26:36 +00:00
IVUsers.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
IndirectCallPromotionAnalysis.cpp [llvm] Migrate llvm::make_unique to std::make_unique 2019-08-15 15:54:37 +00:00
InlineCost.cpp [InstSimplify] Rename SimplifyFPUnOp and SimplifyFPBinOp 2019-07-24 12:50:10 +00:00
InstCount.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
InstructionPrecedenceTracking.cpp Make widenable condition transparent for MemoryWriteTracking 2019-02-14 11:10:29 +00:00
InstructionSimplify.cpp [InstSimplify] simplifyUnsignedRangeCheck(): if we know that X != 0, handle more cases (PR43246) 2019-09-08 20:14:15 +00:00
Interval.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
IntervalPartition.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
LLVMBuild.txt Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
LazyBlockFrequencyInfo.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
LazyBranchProbabilityInfo.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
LazyCallGraph.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
LazyValueInfo.cpp [LVI] Look through extractvalue of insertvalue 2019-09-07 12:03:59 +00:00
LegacyDivergenceAnalysis.cpp [llvm] Migrate llvm::make_unique to std::make_unique 2019-08-15 15:54:37 +00:00
Lint.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
Loads.cpp [NFC] Assert preconditions and merge all users into one codepath in Loads.cpp 2019-08-27 23:36:31 +00:00
LoopAccessAnalysis.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
LoopAnalysisManager.cpp [LoopPassManager + MemorySSA] Only enable use of MemorySSA for LPMs known to preserve it. 2019-08-21 17:00:57 +00:00
LoopCacheAnalysis.cpp [llvm] Migrate llvm::make_unique to std::make_unique 2019-08-15 15:54:37 +00:00
LoopInfo.cpp [LOOPINFO] Introduce the loop guard API. 2019-07-25 16:13:18 +00:00
LoopPass.cpp ftime-trace: Trace loop passes 2019-05-31 10:14:04 +00:00
LoopUnrollAnalyzer.cpp [InstSimplify] Rename SimplifyFPUnOp and SimplifyFPBinOp 2019-07-24 12:50:10 +00:00
MemDepPrinter.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
MemDerefPrinter.cpp OpaquePtr: add Type parameter to Loads analysis API. 2019-07-09 11:35:35 +00:00
MemoryBuiltins.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
MemoryDependenceAnalysis.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
MemoryLocation.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
MemorySSA.cpp [MemorySSA] Re-enable MemorySSA use. 2019-09-04 19:16:04 +00:00
MemorySSAUpdater.cpp [MemorySSA] Fix insertUse. 2019-08-27 00:34:47 +00:00
ModuleDebugInfoPrinter.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ModuleSummaryAnalysis.cpp IR. Change strip* family of functions to not look through aliases. 2019-08-22 19:56:14 +00:00
MustExecute.cpp [MustExec] Add a generic "must-be-executed-context" explorer 2019-08-23 15:17:27 +00:00
ObjCARCAliasAnalysis.cpp [AliasAnalysis] Second prototype to cache BasicAA / anyAA state. 2019-03-22 17:22:19 +00:00
ObjCARCAnalysisUtils.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ObjCARCInstKind.cpp [ObjC][ARC] Delete ObjC runtime calls on global variables annotated 2019-06-14 22:06:32 +00:00
OptimizationRemarkEmitter.cpp [llvm] Migrate llvm::make_unique to std::make_unique 2019-08-15 15:54:37 +00:00
OrderedBasicBlock.cpp Recommit "[DSE] Preserve basic block ordering using OrderedBasicBlock." 2019-03-29 14:10:24 +00:00
OrderedInstructions.cpp [llvm] Migrate llvm::make_unique to std::make_unique 2019-08-15 15:54:37 +00:00
PHITransAddr.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
PhiValues.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
PostDominators.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ProfileSummaryInfo.cpp Cleanup: llvm::bsearch -> llvm::partition_point after r364719 2019-06-30 11:19:56 +00:00
PtrUseVisitor.cpp SROA: Allow eliminating addrspacecasted allocas 2019-06-14 21:38:31 +00:00
README.txt
…
RegionInfo.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
RegionPass.cpp [IR] Refactor attribute methods in Function class (NFC) 2019-04-04 22:40:06 +00:00
RegionPrinter.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ScalarEvolution.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
ScalarEvolutionAliasAnalysis.cpp [AliasAnalysis] Second prototype to cache BasicAA / anyAA state. 2019-03-22 17:22:19 +00:00
ScalarEvolutionExpander.cpp [SCEV] Fix for PR42397. SCEVExpander wrongly adds nsw to shl instruction. 2019-07-08 18:03:43 +00:00
ScalarEvolutionNormalization.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ScopedNoAliasAA.cpp [AliasAnalysis] Second prototype to cache BasicAA / anyAA state. 2019-03-22 17:22:19 +00:00
StackSafetyAnalysis.cpp IR. Change strip* family of functions to not look through aliases. 2019-08-22 19:56:14 +00:00
StratifiedSets.h Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
SyncDependenceAnalysis.cpp [SDA] Bug fix: Use IPD outside the loop as divergence bound 2019-04-18 16:17:35 +00:00
SyntheticCountsUtils.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
TargetLibraryInfo.cpp Change TargetLibraryInfo analysis passes to always require Function 2019-09-07 03:09:36 +00:00
TargetTransformInfo.cpp [LLVM][Alignment] Convert isLegalNTStore/isLegalNTLoad to llvm::Align 2019-09-05 13:09:42 +00:00
Trace.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
TypeBasedAliasAnalysis.cpp [AliasAnalysis] Second prototype to cache BasicAA / anyAA state. 2019-03-22 17:22:19 +00:00
TypeMetadataUtils.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ValueLattice.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ValueLatticeUtils.cpp Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
ValueTracking.cpp Refactor isPointerOffset (NFC). 2019-08-19 21:08:04 +00:00
VectorUtils.cpp [Intrinsic] Add the llvm.umul.fix.sat intrinsic 2019-09-07 12:16:14 +00:00

README.txt 

Analysis Opportunities:

//===---------------------------------------------------------------------===//

In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:

  {1,+,3,+,2}<loop>

Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as

  (-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))

In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.

//===---------------------------------------------------------------------===//

In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,

ScalarEvolution is forming this expression:

((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))

This could be folded to

(-1 * (trunc i64 undef to i32))

//===---------------------------------------------------------------------===//