[polly] r281987 - [ScopDetection] Remove redundant checks for endless loops
Tobias Grosser via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 20 10:05:22 PDT 2016
Author: grosser
Date: Tue Sep 20 12:05:22 2016
New Revision: 281987
URL: http://llvm.org/viewvc/llvm-project?rev=281987&view=rev
Log:
[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 <d412vv1n at gmail.com>
Added:
polly/trunk/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll
- copied, changed from r281850, polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll
Removed:
polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll
Modified:
polly/trunk/include/polly/ScopDetectionDiagnostic.h
polly/trunk/lib/Analysis/ScopDetection.cpp
polly/trunk/lib/Analysis/ScopDetectionDiagnostic.cpp
Modified: polly/trunk/include/polly/ScopDetectionDiagnostic.h
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/include/polly/ScopDetectionDiagnostic.h?rev=281987&r1=281986&r2=281987&view=diff
==============================================================================
--- polly/trunk/include/polly/ScopDetectionDiagnostic.h (original)
+++ polly/trunk/include/polly/ScopDetectionDiagnostic.h Tue Sep 20 12:05:22 2016
@@ -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
//@{
Modified: polly/trunk/lib/Analysis/ScopDetection.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopDetection.cpp?rev=281987&r1=281986&r2=281987&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/ScopDetection.cpp (original)
+++ polly/trunk/lib/Analysis/ScopDetection.cpp Tue Sep 20 12:05:22 2016
@@ -297,56 +297,10 @@ bool ScopDetection::addOverApproximatedR
// 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<ReportLoopOverlapWithNonAffineSubRegion>(
- Context, /*Assert=*/true, L, AR);
}
return (AllowNonAffineSubLoops || Context.BoxedLoopsSet.empty());
@@ -1057,18 +1011,23 @@ bool ScopDetection::isValidInstruction(I
return invalid<ReportUnknownInst>(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<BasicBlock *, 4> 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<BasicBlock *, 4> 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(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<ReportLoopHasNoExit>(Context, /*Assert=*/true, L);
+
if (canUseISLTripCount(L, Context))
return true;
Modified: polly/trunk/lib/Analysis/ScopDetectionDiagnostic.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopDetectionDiagnostic.cpp?rev=281987&r1=281986&r2=281987&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/ScopDetectionDiagnostic.cpp (original)
+++ polly/trunk/lib/Analysis/ScopDetectionDiagnostic.cpp Tue Sep 20 12:05:22 2016
@@ -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::getEndUserM
}
//===----------------------------------------------------------------------===//
-// 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.";
}
//===----------------------------------------------------------------------===//
Copied: polly/trunk/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll (from r281850, polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll)
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll?p2=polly/trunk/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll&p1=polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll&r1=281850&r2=281987&rev=281987&view=diff
==============================================================================
--- polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll (original)
+++ polly/trunk/test/ScopDetectionDiagnostics/ReportLoopHasNoExit.ll Tue Sep 20 12:05:22 2016
@@ -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}
Removed: polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll?rev=281986&view=auto
==============================================================================
--- polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll (original)
+++ polly/trunk/test/ScopDetectionDiagnostics/ReportLoopOverlapWithNonAffineSubRegion.ll (removed)
@@ -1,112 +0,0 @@
-; 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
-
-; void func (int param0, int N, int *A)
-; {
-; for (int i = 0; i < N; i++)
-; if (param0)
-; while (1)
-; A[i] = 1;
-; else
-; 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.
-
-
-
-target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
-
-; Function Attrs: nounwind uwtable
-define void @func(i32 %param0, i32 %N, i32* %A) #0 !dbg !6 {
-entry:
- %param0.addr = alloca i32, align 4
- %N.addr = alloca i32, align 4
- %A.addr = alloca i32*, align 8
- %i = alloca i32, align 4
- store i32 %param0, i32* %param0.addr, align 4
- store i32 %N, i32* %N.addr, align 4
- store i32* %A, i32** %A.addr, align 8
- store i32 0, i32* %i, align 4
- br label %for.cond
-
-for.cond: ; preds = %for.inc, %entry
- %0 = load i32, i32* %i, align 4
- %1 = load i32, i32* %N.addr, align 4
- %cmp = icmp slt i32 %0, %1
- br i1 %cmp, label %for.body, label %for.end, !dbg !27
-
-for.body: ; preds = %for.cond
- %2 = load i32, i32* %param0.addr, align 4
- %tobool = icmp ne i32 %2, 0
- br i1 %tobool, label %if.then, label %if.else
-
-if.then: ; preds = %for.body
- br label %while.body
-
-while.body: ; preds = %if.then, %while.body
- %3 = load i32, i32* %i, align 4
- %idxprom = sext i32 %3 to i64
- %4 = load i32*, i32** %A.addr, align 8
- %arrayidx = getelementptr inbounds i32, i32* %4, i64 %idxprom
- store i32 1, i32* %arrayidx, align 4
- br label %while.body, !dbg !37
-
-if.else: ; preds = %for.body
- %5 = load i32, i32* %i, align 4
- %idxprom1 = sext i32 %5 to i64
- %6 = load i32*, i32** %A.addr, align 8
- %arrayidx2 = getelementptr inbounds i32, i32* %6, i64 %idxprom1
- store i32 2, i32* %arrayidx2, align 4
- br label %if.end
-
-if.end: ; preds = %if.else
- br label %for.inc
-
-for.inc: ; preds = %if.end
- %7 = load i32, i32* %i, align 4
- %inc = add nsw i32 %7, 1
- store i32 %inc, i32* %i, align 4
- br label %for.cond
-
-for.end: ; preds = %for.cond
- ret void
-}
-
-; Function Attrs: nounwind readnone
-declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
-
-attributes #0 = { nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
-attributes #1 = { nounwind readnone }
-
-!llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!3, !4}
-!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/")
-!2 = !{}
-!3 = !{i32 2, !"Dwarf Version", i32 4}
-!4 = !{i32 2, !"Debug Info Version", i32 3}
-!5 = !{!"clang version 3.9.0 "}
-!6 = distinct !DISubprogram(name: "func", scope: !1, file: !1, line: 1, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
-!19 = distinct !DILexicalBlock(scope: !6, file: !1, line: 3, column: 3)
-!23 = !DILexicalBlockFile(scope: !24, file: !1, discriminator: 1)
-!24 = distinct !DILexicalBlock(scope: !19, file: !1, line: 3, column: 3)
-!27 = !DILocation(line: 3, column: 3, scope: !23)
-!29 = distinct !DILexicalBlock(scope: !30, file: !1, line: 5, column: 9)
-!30 = distinct !DILexicalBlock(scope: !24, file: !1, line: 4, column: 3)
-!33 = distinct !DILexicalBlock(scope: !29, file: !1, line: 6, column: 5)
-!37 = !DILocation(line: 7, column: 7, scope: !38)
-!38 = !DILexicalBlockFile(scope: !33, file: !1, discriminator: 1)
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