From: Tobias Grosser Date: Tue, 20 Sep 2016 17:05:22 +0000 (+0000) Subject: [ScopDetection] Remove redundant checks for endless loops X-Git-Tag: llvmorg-4.0.0-rc1~9317 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=349d1c33685b47e14477763ef1530a6395171f4e;p=platform%2Fupstream%2Fllvm.git [ScopDetection] Remove redundant checks for endless loops Summary: Both `canUseISLTripCount()` and `addOverApproximatedRegion()` contained checks to reject endless loops which are now removed and replaced by a single check in `isValidLoop()`. For reporting such loops the `ReportLoopOverlapWithNonAffineSubRegion` is renamed to `ReportLoopHasNoExit`. The test case `ReportLoopOverlapWithNonAffineSubRegion.ll` is adapted and renamed as well. The schedule generation in `buildSchedule()` is based on the following assumption: Given some block B that is contained in a loop L and a SESE region R, we assume that L is contained in R or the other way around. However, this assumption is broken in the presence of endless loops that are nested inside other loops. Therefore, in order to prevent erroneous behavior in `buildSchedule()`, r265280 introduced a corresponding check in `canUseISLTripCount()` to reject endless loops. Unfortunately, it was possible to bypass this check with -polly-allow-nonaffine-loops which was fixed by adding another check to reject endless loops in `allowOverApproximatedRegion()` in r273905. Hence there existed two separate locations that handled this case. Thank you Johannes Doerfert for helping to provide the above background information. Reviewers: Meinersbur, grosser Subscribers: _jdoerfert, pollydev Differential Revision: https://reviews.llvm.org/D24560 Contributed-by: Matthias Reisinger llvm-svn: 281987 --- diff --git a/polly/include/polly/ScopDetectionDiagnostic.h b/polly/include/polly/ScopDetectionDiagnostic.h index 2bdad7d..125e031 100644 --- a/polly/include/polly/ScopDetectionDiagnostic.h +++ b/polly/include/polly/ScopDetectionDiagnostic.h @@ -84,7 +84,7 @@ enum RejectReasonKind { rrkLastAffFunc, rrkLoopBound, - rrkLoopOverlapWithNonAffineSubRegion, + rrkLoopHasNoExit, rrkFuncCall, rrkNonSimpleMemoryAccess, @@ -511,22 +511,18 @@ public: }; //===----------------------------------------------------------------------===// -/// Captures errors when loop overlap with nonaffine subregion. -class ReportLoopOverlapWithNonAffineSubRegion : public RejectReason { +/// Captures errors when loop has no exit. +class ReportLoopHasNoExit : public RejectReason { //===--------------------------------------------------------------------===// - /// If L and R are set then L and R overlap. - - /// The loop contains stmt overlapping nonaffine subregion. + /// The loop that has no exit. Loop *L; - /// The nonaffine subregion that contains infinite loop. - Region *R; - const DebugLoc Loc; public: - ReportLoopOverlapWithNonAffineSubRegion(Loop *L, Region *R); + ReportLoopHasNoExit(Loop *L) + : RejectReason(rrkLoopHasNoExit), L(L), Loc(L->getStartLoc()) {} /// @name LLVM-RTTI interface //@{ diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp index b891c02..7df5179 100644 --- a/polly/lib/Analysis/ScopDetection.cpp +++ b/polly/lib/Analysis/ScopDetection.cpp @@ -297,56 +297,10 @@ bool ScopDetection::addOverApproximatedRegion(Region *AR, // All loops in the region have to be overapproximated too if there // are accesses that depend on the iteration count. - BoxedLoopsSetTy ARBoxedLoopsSet; - for (BasicBlock *BB : AR->blocks()) { Loop *L = LI->getLoopFor(BB); - if (AR->contains(L)) { + if (AR->contains(L)) Context.BoxedLoopsSet.insert(L); - ARBoxedLoopsSet.insert(L); - } - } - - // Reject if the surrounding loop does not entirely contain the nonaffine - // subregion. - // This can happen because a region can contain BBs that have no path to the - // exit block (Infinite loops, UnreachableInst), but such blocks are never - // part of a loop. - // - // _______________ - // | Loop Header | <-----------. - // --------------- | - // | | - // _______________ ______________ - // | RegionEntry |-----> | RegionExit |-----> - // --------------- -------------- - // | - // _______________ - // | EndlessLoop | <--. - // --------------- | - // | | - // \------------/ - // - // In the example above, the loop (LoopHeader,RegionEntry,RegionExit) is - // neither entirely contained in the region RegionEntry->RegionExit - // (containing RegionEntry,EndlessLoop) nor is the region entirely contained - // in the loop. - // The block EndlessLoop is contained is in the region because - // Region::contains tests whether it is not dominated by RegionExit. This is - // probably to not having to query the PostdominatorTree. - // Instead of an endless loop, a dead end can also be formed by - // UnreachableInst. This case is already caught by isErrorBlock(). We hence - // only have to test whether there is an endless loop not contained in the - // surrounding loop. - BasicBlock *BBEntry = AR->getEntry(); - Loop *L = LI->getLoopFor(BBEntry); - while (L && AR->contains(L)) - L = L->getParentLoop(); - if (L) { - for (const auto *ARBoxedLoop : ARBoxedLoopsSet) - if (!L->contains(ARBoxedLoop)) - return invalid( - Context, /*Assert=*/true, L, AR); } return (AllowNonAffineSubLoops || Context.BoxedLoopsSet.empty()); @@ -1057,18 +1011,23 @@ bool ScopDetection::isValidInstruction(Instruction &Inst, return invalid(Context, /*Assert=*/true, &Inst); } +/// Check whether @p L has exiting blocks. +/// +/// @param L The loop of interest +/// +/// @return True if the loop has exiting blocks, false otherwise. +static bool hasExitingBlocks(Loop *L) { + SmallVector ExitingBlocks; + L->getExitingBlocks(ExitingBlocks); + return !ExitingBlocks.empty(); +} + bool ScopDetection::canUseISLTripCount(Loop *L, DetectionContext &Context) const { // Ensure the loop has valid exiting blocks as well as latches, otherwise we // need to overapproximate it as a boxed loop. SmallVector LoopControlBlocks; L->getExitingBlocks(LoopControlBlocks); - - // Loops without exiting blocks cannot be handled by the schedule generation - // as it depends on a region covering that is not given. - if (LoopControlBlocks.empty()) - return false; - L->getLoopLatches(LoopControlBlocks); for (BasicBlock *ControlBB : LoopControlBlocks) { if (!isValidCFG(*ControlBB, true, false, Context)) @@ -1080,6 +1039,38 @@ bool ScopDetection::canUseISLTripCount(Loop *L, } bool ScopDetection::isValidLoop(Loop *L, DetectionContext &Context) const { + // Loops that contain part but not all of the blocks of a region cannot be + // handled by the schedule generation. Such loop constructs can happen + // because a region can contain BBs that have no path to the exit block + // (Infinite loops, UnreachableInst), but such blocks are never part of a + // loop. + // + // _______________ + // | Loop Header | <-----------. + // --------------- | + // | | + // _______________ ______________ + // | RegionEntry |-----> | RegionExit |-----> + // --------------- -------------- + // | + // _______________ + // | EndlessLoop | <--. + // --------------- | + // | | + // \------------/ + // + // In the example above, the loop (LoopHeader,RegionEntry,RegionExit) is + // neither entirely contained in the region RegionEntry->RegionExit + // (containing RegionEntry,EndlessLoop) nor is the region entirely contained + // in the loop. + // The block EndlessLoop is contained in the region because Region::contains + // tests whether it is not dominated by RegionExit. This is probably to not + // having to query the PostdominatorTree. Instead of an endless loop, a dead + // end can also be formed by an UnreachableInst. This case is already caught + // by isErrorBlock(). We hence only have to reject endless loops here. + if (!hasExitingBlocks(L)) + return invalid(Context, /*Assert=*/true, L); + if (canUseISLTripCount(L, Context)) return true; diff --git a/polly/lib/Analysis/ScopDetectionDiagnostic.cpp b/polly/lib/Analysis/ScopDetectionDiagnostic.cpp index e74073c..eb65dc2 100644 --- a/polly/lib/Analysis/ScopDetectionDiagnostic.cpp +++ b/polly/lib/Analysis/ScopDetectionDiagnostic.cpp @@ -43,8 +43,6 @@ using namespace llvm; BADSCOP_STAT(CFG, "CFG too complex"); BADSCOP_STAT(LoopBound, "Loop bounds can not be computed"); -BADSCOP_STAT(LoopOverlapWithNonAffineSubRegion, - "Loop overlap with nonaffine subregion"); BADSCOP_STAT(FuncCall, "Function call with side effects appeared"); BADSCOP_STAT(AffFunc, "Expression not affine"); BADSCOP_STAT(Alias, "Found base address alias"); @@ -330,30 +328,20 @@ std::string ReportLoopBound::getEndUserMessage() const { } //===----------------------------------------------------------------------===// -// ReportLoopOverlapWithNonAffineSubRegion. +// ReportLoopHasNoExit. -ReportLoopOverlapWithNonAffineSubRegion:: - ReportLoopOverlapWithNonAffineSubRegion(Loop *L, Region *R) - : RejectReason(rrkLoopOverlapWithNonAffineSubRegion), L(L), R(R), - Loc(L->getStartLoc()) { - ++BadLoopOverlapWithNonAffineSubRegionForScop; +std::string ReportLoopHasNoExit::getMessage() const { + return "Loop " + L->getHeader()->getName() + " has no exit."; } -std::string ReportLoopOverlapWithNonAffineSubRegion::getMessage() const { - return "Non affine subregion: " + R->getNameStr() + " overlaps Loop " + - L->getHeader()->getName(); +bool ReportLoopHasNoExit::classof(const RejectReason *RR) { + return RR->getKind() == rrkLoopHasNoExit; } -const DebugLoc &ReportLoopOverlapWithNonAffineSubRegion::getDebugLoc() const { - return Loc; -} - -bool ReportLoopOverlapWithNonAffineSubRegion::classof(const RejectReason *RR) { - return RR->getKind() == rrkLoopOverlapWithNonAffineSubRegion; -} +const DebugLoc &ReportLoopHasNoExit::getDebugLoc() const { return Loc; } -std::string ReportLoopOverlapWithNonAffineSubRegion::getEndUserMessage() const { - return "Loop overlaps with nonaffine subregion."; +std::string ReportLoopHasNoExit::getEndUserMessage() const { + return "Loop cannot be handled because it has no exit."; } //===----------------------------------------------------------------------===// diff --git a/polly/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll b/polly/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll similarity index 76% rename from polly/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll rename to polly/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll index 87b78a3..979c339 100644 --- a/polly/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll +++ b/polly/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll @@ -1,5 +1,5 @@ -; RUN: opt %loadPolly -pass-remarks-missed="polly-detect" -polly-allow-nonaffine-loops -analyze -polly-detect < %s 2>&1 | FileCheck %s --check-prefix=REJECTLOOPOVERLAPREGION -; RUN: opt %loadPolly -pass-remarks-missed="polly-detect" -polly-allow-nonaffine-loops=false -analyze -polly-detect < %s 2>&1 | FileCheck %s --check-prefix=REJECTNONAFFINELOOPS +; RUN: opt %loadPolly -pass-remarks-missed="polly-detect" -polly-allow-nonaffine-loops -analyze -polly-detect < %s 2>&1 | FileCheck %s +; RUN: opt %loadPolly -pass-remarks-missed="polly-detect" -polly-allow-nonaffine-loops=false -analyze -polly-detect < %s 2>&1 | FileCheck %s ; void func (int param0, int N, int *A) ; { @@ -11,18 +11,7 @@ ; A[i] = 2; ; } -; If we reject non-affine region and loop will be reported: -; -; REJECTLOOPOVERLAPREGION: remark: ReportLoopOverlapWithNonAffineRegion.c:3:3: The following errors keep this region from being a Scop. -; REJECTLOOPOVERLAPREGION: remark: ReportLoopOverlapWithNonAffineRegion.c:3:3: Loop overlaps with nonaffine subregion. -; REJECTLOOPOVERLAPREGION: remark: ReportLoopOverlapWithNonAffineRegion.c:7:7: Failed to derive an affine function from the loop bounds. -; REJECTLOOPOVERLAPREGION: remark: ReportLoopOverlapWithNonAffineRegion.c:7:7: Invalid Scop candidate ends here. -; -; If we reject non-affine loops the non-affine loop bound will be reported: -; -; REJECTNONAFFINELOOPS: remark: ReportLoopOverlapWithNonAffineRegion.c:7:7: The following errors keep this region from being a Scop. -; REJECTNONAFFINELOOPS: remark: ReportLoopOverlapWithNonAffineRegion.c:7:7: Failed to derive an affine function from the loop bounds. -; REJECTNONAFFINELOOPS: remark: ReportLoopOverlapWithNonAffineRegion.c:7:7: Invalid Scop candidate ends here. +; CHECK: remark: ReportLoopHasNoExit.c:7:7: Loop cannot be handled because it has no exit. @@ -95,7 +84,7 @@ attributes #1 = { nounwind readnone } !llvm.ident = !{!5} !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0 ", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2) -!1 = !DIFile(filename: "ReportLoopOverlapWithNonAffineRegion.c", directory: "test/ScopDetectionDiagnostics/") +!1 = !DIFile(filename: "ReportLoopHasNoExit.c", directory: "test/ScopDetectionDiagnostics/") !2 = !{} !3 = !{i32 2, !"Dwarf Version", i32 4} !4 = !{i32 2, !"Debug Info Version", i32 3}