[llvm] r268254 - [SimplifyCFG] Extend TryToSimplifyUncondBranchFromEmptyBlock for empty block including lifetime intrinsics

Reid Kleckner via llvm-commits llvm-commits at lists.llvm.org
Mon May 2 12:44:22 PDT 2016


We are seeing assertion failures while building Chromium related to this
change:
https://build.chromium.org/p/chromium.fyi/builders/ClangToTLinuxASan/builds/4019/steps/compile/logs/stdio

The uses related to lifetime start / end make me suspect this change, as
well as TryToSimplifyUncondBranchFromEmptyBlock, so I'm going to
speculatively revert for now while I look for a test case.

FAILED: obj/base/files/base.file_posix.o
...
While deleting: i8* %
Use still stuck around after Def is destroyed:  call void
@llvm.lifetime.end(i64 4, i8* <badref>) #11, !dbg !129
Use still stuck around after Def is destroyed:  call void
@llvm.lifetime.end(i64 4, i8* <badref>) #11, !dbg !129
clang-3.9:
/b/build/slave/ClangToTLinuxASan/build/src/third_party/llvm/lib/IR/Value.cpp:85:
virtual llvm::Value::~Value(): Assertion `use_empty() && "Uses remain when
a value is destroyed!"' failed.
0  clang-3.9       0x0000000001a1c945
llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  clang-3.9       0x0000000001a1a6d6 llvm::sys::RunSignalHandlers() + 54
2  clang-3.9       0x0000000001a1a901
3  libpthread.so.0 0x00007f753c5c2cb0
4  libc.so.6       0x00007f753b7ff0d5 gsignal + 53
5  libc.so.6       0x00007f753b80283b abort + 379
6  libc.so.6       0x00007f753b7f7d9e
7  libc.so.6       0x00007f753b7f7e42
8  clang-3.9       0x00000000016d6d0f
9  clang-3.9       0x0000000001679437
10 clang-3.9       0x00000000016161fc llvm::BasicBlock::~BasicBlock() + 140
11 clang-3.9       0x00000000016163b9 llvm::BasicBlock::~BasicBlock() + 9
12 clang-3.9       0x0000000001616722 llvm::BasicBlock::eraseFromParent() +
114
13 clang-3.9       0x0000000001a6b0d3
llvm::TryToSimplifyUncondBranchFromEmptyBlock(llvm::BasicBlock*) + 3923
14 clang-3.9       0x0000000001ab74ea llvm::SimplifyCFG(llvm::BasicBlock*,
llvm::TargetTransformInfo const&, unsigned int, llvm::AssumptionCache*,
llvm::SmallPtrSetImpl<llvm::BasicBlock*>*) + 7914
15 clang-3.9       0x0000000001994c2d

On Mon, May 2, 2016 at 10:22 AM, Hans Wennborg via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: hans
> Date: Mon May  2 12:22:54 2016
> New Revision: 268254
>
> URL: http://llvm.org/viewvc/llvm-project?rev=268254&view=rev
> Log:
> [SimplifyCFG] Extend TryToSimplifyUncondBranchFromEmptyBlock for empty
> block including lifetime intrinsics
>
> Make it possible that TryToSimplifyUncondBranchFromEmptyBlock merges empty
> basic block including lifetime intrinsics as well as phi nodes and
> unconditional branch into its successor or predecessor(s).
>
> If successor of empty block has single predecessor, all contents including
> lifetime intrinsics are sinked into the successor. Otherwise, they are
> hoisted into its predecessor(s) and then merged into the predecessor(s).
>
> Patch by Josh Yoon <josh.yoon at samsung.com>!
>
> Differential Revision: http://reviews.llvm.org/D19257
>
> Modified:
>     llvm/trunk/include/llvm/IR/BasicBlock.h
>     llvm/trunk/lib/IR/BasicBlock.cpp
>     llvm/trunk/lib/Transforms/Utils/Local.cpp
>     llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
>     llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll
>
> Modified: llvm/trunk/include/llvm/IR/BasicBlock.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/BasicBlock.h?rev=268254&r1=268253&r2=268254&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/IR/BasicBlock.h (original)
> +++ llvm/trunk/include/llvm/IR/BasicBlock.h Mon May  2 12:22:54 2016
> @@ -152,6 +152,15 @@ public:
>      return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
>    }
>
> +  /// \brief Returns a pointer to the first instruction in this block
> that is
> +  /// not a PHINode, a debug intrinsic, a lifetime intrinsic, or a bitcast
> +  /// instruction coupled with the following lifetime intrinsic.
> +  Instruction *getFirstNonPHIOrDbgOrLifetimeOrBitCast();
> +  const Instruction *getFirstNonPHIOrDbgOrLifetimeOrBitCast() const {
> +    return const_cast<BasicBlock *>(this)
> +        ->getFirstNonPHIOrDbgOrLifetimeOrBitCast();
> +  }
> +
>    /// \brief Returns an iterator to the first instruction in this block
> that is
>    /// suitable for inserting a non-PHI instruction.
>    ///
>
> Modified: llvm/trunk/lib/IR/BasicBlock.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/BasicBlock.cpp?rev=268254&r1=268253&r2=268254&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/IR/BasicBlock.cpp (original)
> +++ llvm/trunk/lib/IR/BasicBlock.cpp Mon May  2 12:22:54 2016
> @@ -206,6 +206,30 @@ Instruction* BasicBlock::getFirstNonPHIO
>    return nullptr;
>  }
>
> +Instruction *BasicBlock::getFirstNonPHIOrDbgOrLifetimeOrBitCast() {
> +  for (Instruction &I : *this) {
> +    if (isa<PHINode>(I) || isa<DbgInfoIntrinsic>(I))
> +      continue;
> +
> +    if (auto *II = dyn_cast<IntrinsicInst>(&I))
> +      if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
> +          II->getIntrinsicID() == Intrinsic::lifetime_end)
> +        continue;
> +
> +    if (auto *BCI = dyn_cast<BitCastInst>(&I)) {
> +      if (auto *II = dyn_cast<IntrinsicInst>(++I.getIterator())) {
> +        if ((II->getIntrinsicID() == Intrinsic::lifetime_start ||
> +             II->getIntrinsicID() == Intrinsic::lifetime_end) &&
> +            II->getOperand(1) == BCI) {
> +          continue;
> +        }
> +      }
> +    }
> +    return &I;
> +  }
> +  return nullptr;
> +}
> +
>  BasicBlock::iterator BasicBlock::getFirstInsertionPt() {
>    Instruction *FirstNonPHI = getFirstNonPHI();
>    if (!FirstNonPHI)
>
> Modified: llvm/trunk/lib/Transforms/Utils/Local.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/Local.cpp?rev=268254&r1=268253&r2=268254&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/Local.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/Local.cpp Mon May  2 12:22:54 2016
> @@ -800,6 +800,55 @@ static void redirectValuesFromPredecesso
>    replaceUndefValuesInPhi(PN, IncomingValues);
>  }
>
> +/// Return true if BB has lifetime.end intrinsic.
> +///
> +static bool hasLifetime(BasicBlock *BB) {
> +  for (auto &I : *BB) {
> +    if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I)) {
> +      if (II->getIntrinsicID() == Intrinsic::lifetime_end ||
> +          II->getIntrinsicID() == Intrinsic::lifetime_start) {
> +        return true;
> +      }
> +    }
> +  }
> +  return false;
> +}
> +
> +/// hoistLifetimeFromEmptyBlockToPred - Hoist lifetime.end intrinsics and
> +/// related bitcast instructions from BB to predecessors of BB.
> +///
> +static bool hoistLifetimeFromEmptyBlockToPred(BasicBlock *BB) {
> +  // Check to see if all Preds have single successor and if not, we cannot
> +  // hoist lifetime intrinsics because it would change semantics.
> +  for (auto Pred : predecessors(BB))
> +    if (!Pred->getSingleSuccessor())
> +      return false;
> +
> +  // Hoist all lifetime.end intrinsics and related bitcast instrunctions
> +  // in BB to Preds.
> +  for (auto &I : *BB) {
> +    if (auto *II = dyn_cast<IntrinsicInst>(&I)) {
> +      if (II->getIntrinsicID() == Intrinsic::lifetime_end ||
> +          II->getIntrinsicID() == Intrinsic::lifetime_start) {
> +        for (auto Pred : predecessors(BB)) {
> +          Instruction *NewII = I.clone();
> +          NewII->insertBefore(Pred->getTerminator());
> +
> +          if (I.getIterator() != BB->begin()) {
> +            if (auto BC = dyn_cast<BitCastInst>(--I.getIterator())) {
> +              assert(BC == I.getOperand(1));
> +              auto NewBC = BC->clone();
> +              NewBC->insertBefore(NewII);
> +              NewII->setOperand(1, NewBC);
> +            }
> +          }
> +        }
> +      }
> +    }
> +  }
> +  return true;
> +}
> +
>  /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
>  /// unconditional branch, and contains no instructions other than PHI
> nodes,
>  /// potential side-effect free intrinsics and the branch.  If possible,
> @@ -813,74 +862,118 @@ bool llvm::TryToSimplifyUncondBranchFrom
>    BasicBlock *Succ =
> cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
>    if (BB == Succ) return false;
>
> -  // Check to see if merging these blocks would cause conflicts for any
> of the
> -  // phi nodes in BB or Succ. If not, we can safely merge.
> -  if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
> -
> -  // Check for cases where Succ has multiple predecessors and a PHI node
> in BB
> -  // has uses which will not disappear when the PHI nodes are merged.  It
> is
> -  // possible to handle such cases, but difficult: it requires checking
> whether
> -  // BB dominates Succ, which is non-trivial to calculate in the case
> where
> -  // Succ has multiple predecessors.  Also, it requires checking whether
> -  // constructing the necessary self-referential PHI node doesn't
> introduce any
> -  // conflicts; this isn't too difficult, but the previous code for doing
> this
> -  // was incorrect.
> -  //
> -  // Note that if this check finds a live use, BB dominates Succ, so BB is
> -  // something like a loop pre-header (or rarely, a part of an
> irreducible CFG);
> -  // folding the branch isn't profitable in that case anyway.
> -  if (!Succ->getSinglePredecessor()) {
> -    BasicBlock::iterator BBI = BB->begin();
> -    while (isa<PHINode>(*BBI)) {
> -      for (Use &U : BBI->uses()) {
> -        if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
> -          if (PN->getIncomingBlock(U) != BB)
> -            return false;
> -        } else {
> -          return false;
> -        }
> +  // If BB has lifetime.end intrinsics, simplify BB under more
> constraints.
> +  if (hasLifetime(BB)) {
> +    // Check to see if BB and its predecessors and successors have PHI.
> +    if (isa<PHINode>(BB->begin()))
> +      return false;
> +
> +    for (auto Pred : predecessors(BB))
> +      if (isa<PHINode>(Pred->begin()))
> +        return false;
> +
> +    for (auto Succ : successors(BB))
> +      if (isa<PHINode>(Succ->begin()))
> +        return false;
> +
> +    if (Succ->getSinglePredecessor()) {
> +      // BB is the only predecessor of Succ, so Succ will end up with
> exactly
> +      // the same predecessors BB had.
> +
> +      // Copy over any debug or lifetime instruction.
> +      BB->getTerminator()->eraseFromParent();
> +      Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
> +                                 BB->getInstList());
> +
> +    } else {
> +      // Unless BB is the only predecessor of Succ, hoist lifetime
> intrinsics
> +      // to predecessors of BB and simplify BB.
> +      if (!hoistLifetimeFromEmptyBlockToPred(BB)) {
> +        return false;
>        }
> -      ++BBI;
>      }
> -  }
>
> -  DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
> +    DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
>
> -  if (isa<PHINode>(Succ->begin())) {
> -    // If there is more than one pred of succ, and there are PHI nodes in
> -    // the successor, then we need to add incoming edges for the PHI nodes
> +    // Everything that jumped to BB now goes to Succ.
> +    BB->replaceAllUsesWith(Succ);
> +    if (!Succ->hasName())
> +      Succ->takeName(BB);
> +    BB->eraseFromParent(); // Delete the old basic block.
> +    return true;
> +  } else {
> +    // Check to see if merging these blocks would cause conflicts for any
> of the
> +    // phi nodes in BB or Succ. If not, we can safely merge.
> +    if (!CanPropagatePredecessorsForPHIs(BB, Succ))
> +      return false;
> +
> +    // Check for cases where Succ has multiple predecessors and a PHI
> node in BB
> +    // has uses which will not disappear when the PHI nodes are merged.
> It is
> +    // possible to handle such cases, but difficult: it requires checking
> +    // whether BB dominates Succ, which is non-trivial to calculate in the
> +    // case where Succ has multiple predecessors.  Also, it requires
> checking
> +    // whether constructing the necessary self-referential PHI node
> doesn't
> +    // introduce any conflicts; this isn't too difficult, but the
> previous code
> +    // for doing this was incorrect.
>      //
> -    const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
> +    // Note that if this check finds a live use, BB dominates Succ, so BB
> is
> +    // something like a loop pre-header (or rarely, a part of an
> irreducible
> +    // CFG);
> +    // folding the branch isn't profitable in that case anyway.
> +    if (!Succ->getSinglePredecessor()) {
> +      BasicBlock::iterator BBI = BB->begin();
> +      while (isa<PHINode>(*BBI)) {
> +        for (Use &U : BBI->uses()) {
> +          if (PHINode *PN = dyn_cast<PHINode>(U.getUser())) {
> +            if (PN->getIncomingBlock(U) != BB)
> +              return false;
> +          } else {
> +            return false;
> +          }
> +        }
> +        ++BBI;
> +      }
> +    }
> +
> +    DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
>
> -    // Loop over all of the PHI nodes in the successor of BB.
> -    for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
> -      PHINode *PN = cast<PHINode>(I);
> +    if (isa<PHINode>(Succ->begin())) {
> +      // If there is more than one pred of succ, and there are PHI nodes
> in
> +      // the successor, then we need to add incoming edges for the PHI
> nodes
> +      //
> +      const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
> +
> +      // Loop over all of the PHI nodes in the successor of BB.
> +      for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
> +        PHINode *PN = cast<PHINode>(I);
>
> -      redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
> +        redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
> +      }
>      }
> -  }
>
> -  if (Succ->getSinglePredecessor()) {
> -    // BB is the only predecessor of Succ, so Succ will end up with
> exactly
> -    // the same predecessors BB had.
> -
> -    // Copy over any phi, debug or lifetime instruction.
> -    BB->getTerminator()->eraseFromParent();
> -    Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
> -                               BB->getInstList());
> -  } else {
> -    while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
> -      // We explicitly check for such uses in
> CanPropagatePredecessorsForPHIs.
> -      assert(PN->use_empty() && "There shouldn't be any uses here!");
> -      PN->eraseFromParent();
> +    if (Succ->getSinglePredecessor()) {
> +      // BB is the only predecessor of Succ, so Succ will end up with
> exactly
> +      // the same predecessors BB had.
> +
> +      // Copy over any phi, debug or lifetime instruction.
> +      BB->getTerminator()->eraseFromParent();
> +      Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
> +                                 BB->getInstList());
> +    } else {
> +      while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
> +        // We explicitly check for such uses in
> CanPropagatePredecessorsForPHIs.
> +        assert(PN->use_empty() && "There shouldn't be any uses here!");
> +        PN->eraseFromParent();
> +      }
>      }
> -  }
>
> -  // Everything that jumped to BB now goes to Succ.
> -  BB->replaceAllUsesWith(Succ);
> -  if (!Succ->hasName()) Succ->takeName(BB);
> -  BB->eraseFromParent();              // Delete the old basic block.
> -  return true;
> +    // Everything that jumped to BB now goes to Succ.
> +    BB->replaceAllUsesWith(Succ);
> +    if (!Succ->hasName())
> +      Succ->takeName(BB);
> +    BB->eraseFromParent(); // Delete the old basic block.
> +    return true;
> +  }
>  }
>
>  /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
>
> Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=268254&r1=268253&r2=268254&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Mon May  2 12:22:54
> 2016
> @@ -5056,14 +5056,15 @@ bool SimplifyCFGOpt::SimplifyUncondBranc
>
>    if (SinkCommon && SinkThenElseCodeToEnd(BI))
>      return true;
> -
> -  // If the Terminator is the only non-phi instruction, simplify the
> block.
> -  // if LoopHeader is provided, check if the block is a loop header
> +  // If the Terminator is the only non-phi instruction except for bitcast
> +  // instruction coupled with the following lifetime intrinsic, simplify
> the
> +  // block. If LoopHeader is provided, check if the block is a loop header
>    // (This is for early invocations before loop simplify and vectorization
>    // to keep canonical loop forms for nested loops.
>    // These blocks can be eliminated when the pass is invoked later
>    // in the back-end.)
> -  BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
> +  BasicBlock::iterator I =
> +      BB->getFirstNonPHIOrDbgOrLifetimeOrBitCast()->getIterator();
>    if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
>        (!LoopHeaders || !LoopHeaders->count(BB)) &&
>        TryToSimplifyUncondBranchFromEmptyBlock(BB))
>
> Modified: llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll?rev=268254&r1=268253&r2=268254&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll (original)
> +++ llvm/trunk/test/Transforms/SimplifyCFG/lifetime.ll Mon May  2 12:22:54
> 2016
> @@ -1,6 +1,9 @@
>  ; RUN: opt < %s -simplifycfg -S | FileCheck %s
>
>  ; Test that a lifetime intrinsic isn't removed because that would change
> semantics
> +; This case is that predecessor(s) of the target empty block (bb0) has
> multiple
> +; successors (bb0 and bb1) and its successor has multiple predecessors
> (entry and
> +; bb0).
>
>  ; CHECK: foo
>  ; CHECK: entry:
> @@ -27,3 +30,232 @@ declare void @f()
>  declare void @llvm.lifetime.start(i64, i8* nocapture) nounwind
>
>  declare void @llvm.lifetime.end(i64, i8* nocapture) nounwind
> +
> +; Test that empty block including lifetime intrinsic and not related
> bitcast
> +; instruction cannot be removed. It is because the block is not empty.
> +
> +; CHECK-LABEL: coo
> +; CHECK-LABEL: entry:
> +; CHECK-LABEL: if.then:
> +; CHECK-LABEL: if.else:
> +; CHECK-LABEL: if.end:
> +; CHECK-LABEL: bb:
> +; CHECK: ret
> +
> +define void @coo(i1 %x, i1 %y) {
> +entry:
> +  %a = alloca i8, align 4
> +  %b = alloca i32, align 4
> +  br label %while.cond
> +
> +while.cond:                                       ; preds = %if.end,
> %entry
> +  br i1 %y, label %while.body, label %bb
> +
> +while.body:                                       ; preds = %while.cond
> +  call void @llvm.lifetime.start(i64 4, i8* %a)
> +  %c = load i8, i8* %a, align 4
> +  br i1 %x, label %if.then, label %if.else
> +
> +if.then:                                          ; preds = %while.body
> +  %d = add i8 %c, 1
> +  br label %if.end
> +
> +if.else:                                          ; preds = %while.body
> +  %e = sub i8 %c, 1
> +  br label %if.end
> +
> +if.end:                                           ; preds = %if.else,
> %if.then
> +  %f = bitcast i32* %b to i8*
> +  call void @llvm.lifetime.end(i64 4, i8* %a)
> +  br label %while.cond
> +
> +bb:                                               ; preds = %while.cond
> +  ret void
> +}
> +
> +; Test that empty block including lifetime intrinsic can be removed.
> +; Lifetime.end intrinsic is moved to predecessors because successor has
> +; multiple predecessors.
> +
> +; CHECK-LABEL: soo
> +; CHECK-LABEL: entry:
> +; CHECK-LABEL: if.then:
> +; CHECK-NEXT: %e
> +; CHECK-NEXT: call void @llvm.lifetime.end
> +; CHECK-LABEL: if.else:
> +; CHECK-NEXT: %g
> +; CHECK-NEXT: call void @llvm.lifetime.end
> +; CHECK-NEXT: br label %while.cond
> +; CHECK-NOT: if.end:
> +; CHECK: ret
> +
> +define void @soo(i1 %x, i1 %y) {
> +entry:
> +  %a = alloca i8, align 4
> +  br label %while.cond
> +
> +while.cond:                                       ; preds = %if.end,
> %entry
> +  br i1 %y, label %while.body, label %bb
> +
> +while.body:                                       ; preds = %while.cond
> +  call void @llvm.lifetime.start(i64 4, i8* %a)
> +  %d = load i8, i8* %a, align 4
> +  br i1 %x, label %if.then, label %if.else
> +
> +if.then:                                          ; preds = %while.body
> +  %e = add i8 %d, 1
> +  br label %if.end
> +
> +if.else:                                          ; preds = %while.body
> +  %g = sub i8 %d, 1
> +  br label %if.end
> +
> +if.end:                                           ; preds = %if.else,
> %if.then
> +  call void @llvm.lifetime.end(i64 4, i8* %a)
> +  br label %while.cond
> +
> +bb:                                               ; preds = %while.cond
> +  ret void
> +}
> +
> +; Test that empty block including lifetime intrinsic and related bitcast
> +; instruction can be removed. Lifetime.end intrinsic and related bitcast
> +; instruction are moved to predecessors because successor has multiple
> +; predecessors.
> +
> +; CHECK-LABEL: boo
> +; CHECK-LABEL: entry:
> +; CHECK-LABEL: if.then:
> +; CHECK-NEXT: %e
> +; CHECK-NEXT: %[[T:[^ ]+]] = bitcast
> +; CHECK-NEXT: call void @llvm.lifetime.end(i64 4, i8* %[[T]])
> +; CHECK-LABEL: if.else:
> +; CHECK-NEXT: %g
> +; CHECK-NEXT: %[[B:[^ ]+]] = bitcast
> +; CHECK-NEXT: call void @llvm.lifetime.end(i64 4, i8* %[[B]])
> +; CHECK-NEXT: br label %while.cond
> +; CHECK-NOT: if.end:
> +; CHECK: ret
> +
> +define void @boo(i1 %x, i1 %y) {
> +entry:
> +  %a = alloca i32, align 4
> +  br label %while.cond
> +
> +while.cond:                                       ; preds = %if.end,
> %entry
> +  br i1 %y, label %while.body, label %bb
> +
> +while.body:                                       ; preds = %while.cond
> +  %b = bitcast i32* %a to i8*
> +  call void @llvm.lifetime.start(i64 4, i8* %b)
> +  %d = load i32, i32* %a, align 4
> +  br i1 %x, label %if.then, label %if.else
> +
> +if.then:                                          ; preds = %while.body
> +  %e = add i32 %d, 1
> +  br label %if.end
> +
> +if.else:                                          ; preds = %while.body
> +  %g = sub i32 %d, 1
> +  br label %if.end
> +
> +if.end:                                           ; preds = %if.else,
> %if.then
> +  %c = bitcast i32* %a to i8*
> +  call void @llvm.lifetime.end(i64 4, i8* %c)
> +  br label %while.cond
> +
> +bb:                                               ; preds = %while.cond
> +  ret void
> +}
> +
> +; Test that empty block including lifetime intrinsic can be removed.
> +; Lifetime.start intrinsic is moved to predecessors because successor has
> +; multiple predecessors.
> +
> +; CHECK-LABEL: koo
> +; CHECK-LABEL: entry:
> +; CHECK-LABEL: if.then:
> +; CHECK-NEXT: call void @f
> +; CHECK-NEXT: call void @llvm.lifetime.start
> +; CHECK-LABEL: if.else:
> +; CHECK-NEXT: call void @g
> +; CHECK-NEXT: call void @llvm.lifetime.start
> +; CHECK-NEXT: br label %bb
> +; CHECK-NOT: if.end:
> +; CHECK: ret
> +
> +define void @koo(i1 %x, i1 %y, i1 %z) {
> +entry:
> +  %a = alloca i8, align 4
> +  br i1 %z, label %bb, label %bb0
> +
> +bb0:                                              ; preds = %entry
> +  br i1 %x, label %if.then, label %if.else
> +
> +if.then:                                          ; preds = %bb0
> +  call void @f()
> +  br label %if.end
> +
> +if.else:                                          ; preds = %bb0
> +  call void @g()
> +  br label %if.end
> +
> +if.end:                                           ; preds = %if.else,
> %if.then
> +  call void @llvm.lifetime.start(i64 4, i8* %a)
> +  br label %bb
> +
> +bb:                                               ; preds = %if.end,
> %entry
> +  %d = load i8, i8* %a, align 4
> +  call void @llvm.lifetime.end(i64 4, i8* %a)
> +  ret void
> +}
> +
> +declare void @g()
> +
> +; Test that empty block including lifetime intrinsic and related bitcast
> +; instruction can be removed. Lifetime.start intrinsic and related bitcast
> +; instruction are moved to predecessors because successor has multiple
> +; predecessors.
> +
> +
> +; CHECK-LABEL: goo
> +; CHECK-LABEL: entry:
> +; CHECK-LABEL: if.then:
> +; CHECK-NEXT: call void @f
> +; CHECK-NEXT: %[[T:[^ ]+]] = bitcast
> +; CHECK-NEXT: call void @llvm.lifetime.start(i64 4, i8* %[[T]])
> +; CHECK-LABEL: if.else:
> +; CHECK-NEXT: call void @g
> +; CHECK-NEXT: %[[B:[^ ]+]] = bitcast
> +; CHECK-NEXT: call void @llvm.lifetime.start(i64 4, i8* %[[B]])
> +; CHECK-NEXT: br label %bb
> +; CHECK-NOT: if.end:
> +; CHECK: ret
> +
> +define void @goo(i1 %x, i1 %y, i1 %z) {
> +entry:
> +  %a = alloca i32, align 4
> +  br i1 %z, label %bb, label %bb0
> +
> +bb0:                                              ; preds = %entry
> +  br i1 %x, label %if.then, label %if.else
> +
> +if.then:                                          ; preds = %bb0
> +  call void @f()
> +  br label %if.end
> +
> +if.else:                                          ; preds = %bb0
> +  call void @g()
> +  br label %if.end
> +
> +if.end:                                           ; preds = %if.else,
> %if.then
> +  %b = bitcast i32* %a to i8*
> +  call void @llvm.lifetime.start(i64 4, i8* %b)
> +  br label %bb
> +
> +bb:                                               ; preds = %if.end,
> %entry
> +  %d = load i32, i32* %a, align 4
> +  %c = bitcast i32* %a to i8*
> +  call void @llvm.lifetime.end(i64 4, i8* %c)
> +  ret void
> +}
>
>
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