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[LoopUnroll] Fix a crash
Loop peeling as a last step triggers loop simplification and this can change the loop structure. As a result all cashed values like latch branch becomes invalid. Patch re-structure the code to take into account the possible changes caused by peeling. Reviewers: dmgreen, Meinersbur, etiotto, fhahn, efriedma, bmahjour Reviewed By: Meinersbur, fhahn Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D93686
This commit is contained in:
Serguei Katkov
parent
c1a38e0929
commit
d6cc630830
@ -288,14 +288,12 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
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OptimizationRemarkEmitter *ORE,
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bool PreserveLCSSA, Loop **RemainderLoop) {
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BasicBlock *Preheader = L->getLoopPreheader();
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if (!Preheader) {
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if (!L->getLoopPreheader()) {
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LLVM_DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
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return LoopUnrollResult::Unmodified;
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}
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BasicBlock *LatchBlock = L->getLoopLatch();
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if (!LatchBlock) {
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if (!L->getLoopLatch()) {
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LLVM_DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n");
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return LoopUnrollResult::Unmodified;
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}
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@ -306,37 +304,7 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
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return LoopUnrollResult::Unmodified;
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}
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// The current loop unroll pass can unroll loops that have
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// (1) single latch; and
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// (2a) latch is unconditional; or
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// (2b) latch is conditional and is an exiting block
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// FIXME: The implementation can be extended to work with more complicated
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// cases, e.g. loops with multiple latches.
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BasicBlock *Header = L->getHeader();
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BranchInst *LatchBI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
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// A conditional branch which exits the loop, which can be optimized to an
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// unconditional branch in the unrolled loop in some cases.
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BranchInst *ExitingBI = nullptr;
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bool LatchIsExiting = L->isLoopExiting(LatchBlock);
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if (LatchIsExiting)
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ExitingBI = LatchBI;
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else if (BasicBlock *ExitingBlock = L->getExitingBlock())
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ExitingBI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
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if (!LatchBI || (LatchBI->isConditional() && !LatchIsExiting)) {
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LLVM_DEBUG(
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dbgs() << "Can't unroll; a conditional latch must exit the loop");
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return LoopUnrollResult::Unmodified;
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}
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LLVM_DEBUG({
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if (ExitingBI)
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dbgs() << " Exiting Block = " << ExitingBI->getParent()->getName()
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<< "\n";
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else
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dbgs() << " No single exiting block\n";
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});
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if (Header->hasAddressTaken()) {
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if (L->getHeader()->hasAddressTaken()) {
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// The loop-rotate pass can be helpful to avoid this in many cases.
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LLVM_DEBUG(
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dbgs() << " Won't unroll loop: address of header block is taken.\n");
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@ -365,20 +333,6 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
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// Are we eliminating the loop control altogether?
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bool CompletelyUnroll = ULO.Count == ULO.TripCount;
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SmallVector<BasicBlock *, 4> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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std::vector<BasicBlock*> OriginalLoopBlocks = L->getBlocks();
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// Go through all exits of L and see if there are any phi-nodes there. We just
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// conservatively assume that they're inserted to preserve LCSSA form, which
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// means that complete unrolling might break this form. We need to either fix
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// it in-place after the transformation, or entirely rebuild LCSSA. TODO: For
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// now we just recompute LCSSA for the outer loop, but it should be possible
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// to fix it in-place.
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bool NeedToFixLCSSA = PreserveLCSSA && CompletelyUnroll &&
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any_of(ExitBlocks, [](const BasicBlock *BB) {
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return isa<PHINode>(BB->begin());
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});
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// We assume a run-time trip count if the compiler cannot
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// figure out the loop trip count and the unroll-runtime
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@ -403,12 +357,63 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
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BasicBlock *ExitingBlock = L->getLoopLatch();
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assert(ExitingBlock && "Loop without exiting block?");
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assert(L->isLoopExiting(ExitingBlock) && "Latch is not exiting?");
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Preheader = L->getLoopPreheader();
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ULO.TripCount = SE->getSmallConstantTripCount(L, ExitingBlock);
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ULO.TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock);
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}
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}
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// All these values should be taken only after peeling because they might have
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// changed.
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BasicBlock *Preheader = L->getLoopPreheader();
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BasicBlock *Header = L->getHeader();
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BasicBlock *LatchBlock = L->getLoopLatch();
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SmallVector<BasicBlock *, 4> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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std::vector<BasicBlock *> OriginalLoopBlocks = L->getBlocks();
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// Go through all exits of L and see if there are any phi-nodes there. We just
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// conservatively assume that they're inserted to preserve LCSSA form, which
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// means that complete unrolling might break this form. We need to either fix
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// it in-place after the transformation, or entirely rebuild LCSSA. TODO: For
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// now we just recompute LCSSA for the outer loop, but it should be possible
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// to fix it in-place.
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bool NeedToFixLCSSA =
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PreserveLCSSA && CompletelyUnroll &&
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any_of(ExitBlocks,
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[](const BasicBlock *BB) { return isa<PHINode>(BB->begin()); });
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// The current loop unroll pass can unroll loops that have
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// (1) single latch; and
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// (2a) latch is unconditional; or
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// (2b) latch is conditional and is an exiting block
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// FIXME: The implementation can be extended to work with more complicated
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// cases, e.g. loops with multiple latches.
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BranchInst *LatchBI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
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// A conditional branch which exits the loop, which can be optimized to an
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// unconditional branch in the unrolled loop in some cases.
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BranchInst *ExitingBI = nullptr;
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bool LatchIsExiting = L->isLoopExiting(LatchBlock);
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if (LatchIsExiting)
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ExitingBI = LatchBI;
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else if (BasicBlock *ExitingBlock = L->getExitingBlock())
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ExitingBI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
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if (!LatchBI || (LatchBI->isConditional() && !LatchIsExiting)) {
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// If the peeling guard is changed this assert may be relaxed or even
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// deleted.
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assert(!Peeled && "Peeling guard changed!");
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LLVM_DEBUG(
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dbgs() << "Can't unroll; a conditional latch must exit the loop");
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return LoopUnrollResult::Unmodified;
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}
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LLVM_DEBUG({
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if (ExitingBI)
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dbgs() << " Exiting Block = " << ExitingBI->getParent()->getName()
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<< "\n";
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else
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dbgs() << " No single exiting block\n";
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});
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// Loops containing convergent instructions must have a count that divides
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// their TripMultiple.
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LLVM_DEBUG(
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48
test/Transforms/LoopUnroll/unroll-after-peel.ll
Normal file
48
test/Transforms/LoopUnroll/unroll-after-peel.ll
Normal file
@ -0,0 +1,48 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -passes=loop-unroll -S | FileCheck %s
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define i64 @hoge(i1 %c) {
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; CHECK-LABEL: @hoge(
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; CHECK-NEXT: bb:
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; CHECK-NEXT: br label [[BB1_PEEL_BEGIN:%.*]]
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; CHECK: bb1.peel.begin:
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; CHECK-NEXT: br label [[BB1_PEEL:%.*]]
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; CHECK: bb1.peel:
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; CHECK-NEXT: br i1 [[C:%.*]], label [[BB2_PEEL:%.*]], label [[BB4:%.*]]
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; CHECK: bb2.peel:
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; CHECK-NEXT: [[TMP3_PEEL:%.*]] = icmp slt i32 0, 9
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; CHECK-NEXT: br i1 [[TMP3_PEEL]], label [[BB1_PEEL_NEXT:%.*]], label [[BB4]]
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; CHECK: bb1.peel.next:
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; CHECK-NEXT: br label [[BB1_PEEL_NEXT1:%.*]]
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; CHECK: bb1.peel.next1:
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; CHECK-NEXT: br label [[BB_PEEL_NEWPH:%.*]]
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; CHECK: bb.peel.newph:
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; CHECK-NEXT: br label [[BB1:%.*]]
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; CHECK: bb1:
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; CHECK-NEXT: br i1 [[C]], label [[BB1]], label [[BB4_LOOPEXIT:%.*]], [[LOOP0:!llvm.loop !.*]]
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; CHECK: bb4.loopexit:
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; CHECK-NEXT: [[TMP5_PH:%.*]] = phi i32 [ 8, [[BB1]] ]
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; CHECK-NEXT: br label [[BB4]]
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; CHECK: bb4:
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; CHECK-NEXT: [[TMP5:%.*]] = phi i32 [ 0, [[BB1_PEEL]] ], [ 8, [[BB2_PEEL]] ], [ [[TMP5_PH]], [[BB4_LOOPEXIT]] ]
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; CHECK-NEXT: [[TMP6:%.*]] = call i64 (...) @llvm.experimental.deoptimize.i64(i32 10) [ "deopt"() ]
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; CHECK-NEXT: ret i64 [[TMP6]]
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;
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bb:
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br label %bb1
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bb1: ; preds = %bb2, %bb
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%tmp = phi i32 [ 8, %bb2 ], [ 0, %bb ]
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br i1 %c, label %bb2, label %bb4
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bb2: ; preds = %bb1
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%tmp3 = icmp slt i32 %tmp, 9
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br i1 %tmp3, label %bb1, label %bb4
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bb4: ; preds = %bb2, %bb1
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%tmp5 = phi i32 [ 8, %bb2 ], [ %tmp, %bb1 ]
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%tmp6 = call i64 (...) @llvm.experimental.deoptimize.i64(i32 10) [ "deopt"() ]
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ret i64 %tmp6
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}
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declare i64 @llvm.experimental.deoptimize.i64(...)
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