[llvm] 7f69860 - [LoopUnroll] Fix a crash
Serguei Katkov via llvm-commits
llvm-commits at lists.llvm.org
Sun Jan 10 19:30:54 PST 2021
Author: Serguei Katkov
Date: 2021-01-11T10:19:26+07:00
New Revision: 7f69860243e8933c3da1177afde0d3cb6544d04e
URL: https://github.com/llvm/llvm-project/commit/7f69860243e8933c3da1177afde0d3cb6544d04e
DIFF: https://github.com/llvm/llvm-project/commit/7f69860243e8933c3da1177afde0d3cb6544d04e.diff
LOG: [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
Added:
llvm/test/Transforms/LoopUnroll/unroll-after-peel.ll
Modified:
llvm/lib/Transforms/Utils/LoopUnroll.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 4d5d03528633..6478143545ab 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -288,14 +288,12 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
OptimizationRemarkEmitter *ORE,
bool PreserveLCSSA, Loop **RemainderLoop) {
- BasicBlock *Preheader = L->getLoopPreheader();
- if (!Preheader) {
+ if (!L->getLoopPreheader()) {
LLVM_DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
return LoopUnrollResult::Unmodified;
}
- BasicBlock *LatchBlock = L->getLoopLatch();
- if (!LatchBlock) {
+ if (!L->getLoopLatch()) {
LLVM_DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n");
return LoopUnrollResult::Unmodified;
}
@@ -306,37 +304,7 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
return LoopUnrollResult::Unmodified;
}
- // The current loop unroll pass can unroll loops that have
- // (1) single latch; and
- // (2a) latch is unconditional; or
- // (2b) latch is conditional and is an exiting block
- // FIXME: The implementation can be extended to work with more complicated
- // cases, e.g. loops with multiple latches.
- BasicBlock *Header = L->getHeader();
- BranchInst *LatchBI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
-
- // A conditional branch which exits the loop, which can be optimized to an
- // unconditional branch in the unrolled loop in some cases.
- BranchInst *ExitingBI = nullptr;
- bool LatchIsExiting = L->isLoopExiting(LatchBlock);
- if (LatchIsExiting)
- ExitingBI = LatchBI;
- else if (BasicBlock *ExitingBlock = L->getExitingBlock())
- ExitingBI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
- if (!LatchBI || (LatchBI->isConditional() && !LatchIsExiting)) {
- LLVM_DEBUG(
- dbgs() << "Can't unroll; a conditional latch must exit the loop");
- return LoopUnrollResult::Unmodified;
- }
- LLVM_DEBUG({
- if (ExitingBI)
- dbgs() << " Exiting Block = " << ExitingBI->getParent()->getName()
- << "\n";
- else
- dbgs() << " No single exiting block\n";
- });
-
- if (Header->hasAddressTaken()) {
+ if (L->getHeader()->hasAddressTaken()) {
// The loop-rotate pass can be helpful to avoid this in many cases.
LLVM_DEBUG(
dbgs() << " Won't unroll loop: address of header block is taken.\n");
@@ -365,20 +333,6 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
// Are we eliminating the loop control altogether?
bool CompletelyUnroll = ULO.Count == ULO.TripCount;
- SmallVector<BasicBlock *, 4> ExitBlocks;
- L->getExitBlocks(ExitBlocks);
- std::vector<BasicBlock*> OriginalLoopBlocks = L->getBlocks();
-
- // Go through all exits of L and see if there are any phi-nodes there. We just
- // conservatively assume that they're inserted to preserve LCSSA form, which
- // means that complete unrolling might break this form. We need to either fix
- // it in-place after the transformation, or entirely rebuild LCSSA. TODO: For
- // now we just recompute LCSSA for the outer loop, but it should be possible
- // to fix it in-place.
- bool NeedToFixLCSSA = PreserveLCSSA && CompletelyUnroll &&
- any_of(ExitBlocks, [](const BasicBlock *BB) {
- return isa<PHINode>(BB->begin());
- });
// We assume a run-time trip count if the compiler cannot
// figure out the loop trip count and the unroll-runtime
@@ -403,12 +357,63 @@ LoopUnrollResult llvm::UnrollLoop(Loop *L, UnrollLoopOptions ULO, LoopInfo *LI,
BasicBlock *ExitingBlock = L->getLoopLatch();
assert(ExitingBlock && "Loop without exiting block?");
assert(L->isLoopExiting(ExitingBlock) && "Latch is not exiting?");
- Preheader = L->getLoopPreheader();
ULO.TripCount = SE->getSmallConstantTripCount(L, ExitingBlock);
ULO.TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock);
}
}
+ // All these values should be taken only after peeling because they might have
+ // changed.
+ BasicBlock *Preheader = L->getLoopPreheader();
+ BasicBlock *Header = L->getHeader();
+ BasicBlock *LatchBlock = L->getLoopLatch();
+ SmallVector<BasicBlock *, 4> ExitBlocks;
+ L->getExitBlocks(ExitBlocks);
+ std::vector<BasicBlock *> OriginalLoopBlocks = L->getBlocks();
+
+ // Go through all exits of L and see if there are any phi-nodes there. We just
+ // conservatively assume that they're inserted to preserve LCSSA form, which
+ // means that complete unrolling might break this form. We need to either fix
+ // it in-place after the transformation, or entirely rebuild LCSSA. TODO: For
+ // now we just recompute LCSSA for the outer loop, but it should be possible
+ // to fix it in-place.
+ bool NeedToFixLCSSA =
+ PreserveLCSSA && CompletelyUnroll &&
+ any_of(ExitBlocks,
+ [](const BasicBlock *BB) { return isa<PHINode>(BB->begin()); });
+
+ // The current loop unroll pass can unroll loops that have
+ // (1) single latch; and
+ // (2a) latch is unconditional; or
+ // (2b) latch is conditional and is an exiting block
+ // FIXME: The implementation can be extended to work with more complicated
+ // cases, e.g. loops with multiple latches.
+ BranchInst *LatchBI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
+
+ // A conditional branch which exits the loop, which can be optimized to an
+ // unconditional branch in the unrolled loop in some cases.
+ BranchInst *ExitingBI = nullptr;
+ bool LatchIsExiting = L->isLoopExiting(LatchBlock);
+ if (LatchIsExiting)
+ ExitingBI = LatchBI;
+ else if (BasicBlock *ExitingBlock = L->getExitingBlock())
+ ExitingBI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
+ if (!LatchBI || (LatchBI->isConditional() && !LatchIsExiting)) {
+ // If the peeling guard is changed this assert may be relaxed or even
+ // deleted.
+ assert(!Peeled && "Peeling guard changed!");
+ LLVM_DEBUG(
+ dbgs() << "Can't unroll; a conditional latch must exit the loop");
+ return LoopUnrollResult::Unmodified;
+ }
+ LLVM_DEBUG({
+ if (ExitingBI)
+ dbgs() << " Exiting Block = " << ExitingBI->getParent()->getName()
+ << "\n";
+ else
+ dbgs() << " No single exiting block\n";
+ });
+
// Loops containing convergent instructions must have a count that divides
// their TripMultiple.
LLVM_DEBUG(
diff --git a/llvm/test/Transforms/LoopUnroll/unroll-after-peel.ll b/llvm/test/Transforms/LoopUnroll/unroll-after-peel.ll
new file mode 100644
index 000000000000..8f9afd2c8518
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/unroll-after-peel.ll
@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=loop-unroll -S | FileCheck %s
+
+define i64 @hoge(i1 %c) {
+; CHECK-LABEL: @hoge(
+; CHECK-NEXT: bb:
+; CHECK-NEXT: br label [[BB1_PEEL_BEGIN:%.*]]
+; CHECK: bb1.peel.begin:
+; CHECK-NEXT: br label [[BB1_PEEL:%.*]]
+; CHECK: bb1.peel:
+; CHECK-NEXT: br i1 [[C:%.*]], label [[BB2_PEEL:%.*]], label [[BB4:%.*]]
+; CHECK: bb2.peel:
+; CHECK-NEXT: [[TMP3_PEEL:%.*]] = icmp slt i32 0, 9
+; CHECK-NEXT: br i1 [[TMP3_PEEL]], label [[BB1_PEEL_NEXT:%.*]], label [[BB4]]
+; CHECK: bb1.peel.next:
+; CHECK-NEXT: br label [[BB1_PEEL_NEXT1:%.*]]
+; CHECK: bb1.peel.next1:
+; CHECK-NEXT: br label [[BB_PEEL_NEWPH:%.*]]
+; CHECK: bb.peel.newph:
+; CHECK-NEXT: br label [[BB1:%.*]]
+; CHECK: bb1:
+; CHECK-NEXT: br i1 [[C]], label [[BB1]], label [[BB4_LOOPEXIT:%.*]], [[LOOP0:!llvm.loop !.*]]
+; CHECK: bb4.loopexit:
+; CHECK-NEXT: [[TMP5_PH:%.*]] = phi i32 [ 8, [[BB1]] ]
+; CHECK-NEXT: br label [[BB4]]
+; CHECK: bb4:
+; CHECK-NEXT: [[TMP5:%.*]] = phi i32 [ 0, [[BB1_PEEL]] ], [ 8, [[BB2_PEEL]] ], [ [[TMP5_PH]], [[BB4_LOOPEXIT]] ]
+; CHECK-NEXT: [[TMP6:%.*]] = call i64 (...) @llvm.experimental.deoptimize.i64(i32 10) [ "deopt"() ]
+; CHECK-NEXT: ret i64 [[TMP6]]
+;
+bb:
+ br label %bb1
+
+bb1: ; preds = %bb2, %bb
+ %tmp = phi i32 [ 8, %bb2 ], [ 0, %bb ]
+ br i1 %c, label %bb2, label %bb4
+
+bb2: ; preds = %bb1
+ %tmp3 = icmp slt i32 %tmp, 9
+ br i1 %tmp3, label %bb1, label %bb4
+
+bb4: ; preds = %bb2, %bb1
+ %tmp5 = phi i32 [ 8, %bb2 ], [ %tmp, %bb1 ]
+ %tmp6 = call i64 (...) @llvm.experimental.deoptimize.i64(i32 10) [ "deopt"() ]
+ ret i64 %tmp6
+}
+
+declare i64 @llvm.experimental.deoptimize.i64(...)
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