[llvm-commits] [llvm] r59528 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/2008-11-18-LessThanOrEqual.ll test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll test/Analysis/ScalarEvolution/2008-11-18-Stride2.ll

Nick Lewycky nicholas at mxc.ca
Wed Nov 19 20:41:09 PST 2008


Evan Cheng wrote:
> On Nov 18, 2008, at 7:38 PM, Nick Lewycky wrote:
> 
>> Evan Cheng wrote:
>>> Hi Nicholas,
>>>
>>> What does "trueWhenEqual" mean? Should it default to true / false?
>> Like isSigned, it defines whether the comparison is true when equal,
>> ie., it's an SLT/ULT vs. SLE/ULE. There is no default, but the old
>> version only knew how to handle trueWhenEqual=false (ie., SLT/ULT).
> 
> Can you make the default false? That way old code that use it (which  
> may not be part of the tree) won't have to change.

These are all private methods in the ScalarEvolutionsImpl class (which 
is VISIBILITY_HIDDEN in an anonymous namespace). The public interface in 
llvm/include/Analysis/ScalarEvolution.h hasn't changed.

Nick

> Thanks,
> 
> Evan
> 
>>
>> Nick
>>
>>> Thanks,
>>>
>>> Evan
>>>
>>> On Nov 18, 2008, at 7:10 AM, Nick Lewycky wrote:
>>>
>>>> Author: nicholas
>>>> Date: Tue Nov 18 09:10:54 2008
>>>> New Revision: 59528
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=59528&view=rev
>>>> Log:
>>>> Add a utility function that detects whether a loop is guaranteed to
>>>> be finite.
>>>>
>>>> Use it to safely handle less-than-or-equals-to exit conditions in
>>>> loops. These
>>>> also occur when the loop exit branch is exit on true because SCEV
>>>> inverses the
>>>> icmp predicate.
>>>>
>>>> Use it again to handle non-zero strides, but only with an unsigned
>>>> comparison
>>>> in the exit condition.
>>>>
>>>> Added:
>>>>   llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-
>>>> LessThanOrEqual.ll
>>>>   llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll
>>>>   llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride2.ll
>>>> Modified:
>>>>   llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>>>>
>>>> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=59528&r1=59527&r2=59528&view=diff
>>>>
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> = 
>>>> = 
>>>> ====================================================================
>>>> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
>>>> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Tue Nov 18 09:10:54
>>>> 2008
>>>> @@ -1477,7 +1477,7 @@
>>>>    /// specified less-than comparison will execute.  If not
>>>> computable, return
>>>>    /// UnknownValue. isSigned specifies whether the less-than is
>>>> signed.
>>>>    SCEVHandle HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
>>>> -                                bool isSigned);
>>>> +                                bool isSigned, bool trueWhenEqual);
>>>>
>>>>    /// getPredecessorWithUniqueSuccessorForBB - Return a
>>>> predecessor of BB
>>>>    /// (which may not be an immediate predecessor) which has
>>>> exactly one
>>>> @@ -1487,7 +1487,13 @@
>>>>
>>>>    /// executesAtLeastOnce - Test whether entry to the loop is
>>>> protected by
>>>>    /// a conditional between LHS and RHS.
>>>> -    bool executesAtLeastOnce(const Loop *L, bool isSigned, SCEV
>>>> *LHS, SCEV *RHS);
>>>> +    bool executesAtLeastOnce(const Loop *L, bool isSigned, bool
>>>> trueWhenEqual,
>>>> +                             SCEV *LHS, SCEV *RHS);
>>>> +
>>>> +    /// potentialInfiniteLoop - Test whether the loop might jump
>>>> over the exit value
>>>> +    /// due to wrapping.
>>>> +    bool potentialInfiniteLoop(SCEV *Stride, SCEV *RHS, bool
>>>> isSigned,
>>>> +                               bool trueWhenEqual);
>>>>
>>>>    /// getConstantEvolutionLoopExitValue - If we know that the
>>>> specified Phi is
>>>>    /// in the header of its containing loop, we know the loop
>>>> executes a
>>>> @@ -2025,24 +2031,46 @@
>>>>    break;
>>>>  }
>>>>  case ICmpInst::ICMP_SLT: {
>>>> -    SCEVHandle TC = HowManyLessThans(LHS, RHS, L, true);
>>>> +    SCEVHandle TC = HowManyLessThans(LHS, RHS, L, true, false);
>>>>    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>>    break;
>>>>  }
>>>>  case ICmpInst::ICMP_SGT: {
>>>>    SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
>>>> -                                     SE.getNotSCEV(RHS), L, true);
>>>> +                                     SE.getNotSCEV(RHS), L, true,
>>>> false);
>>>>    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>>    break;
>>>>  }
>>>>  case ICmpInst::ICMP_ULT: {
>>>> -    SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false);
>>>> +    SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false, false);
>>>>    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>>    break;
>>>>  }
>>>>  case ICmpInst::ICMP_UGT: {
>>>>    SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
>>>> -                                     SE.getNotSCEV(RHS), L, false);
>>>> +                                     SE.getNotSCEV(RHS), L, false,
>>>> false);
>>>> +    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>> +    break;
>>>> +  }
>>>> +  case ICmpInst::ICMP_SLE: {
>>>> +    SCEVHandle TC = HowManyLessThans(LHS, RHS, L, true, true);
>>>> +    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>> +    break;
>>>> +  }
>>>> +  case ICmpInst::ICMP_SGE: {
>>>> +    SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
>>>> +                                     SE.getNotSCEV(RHS), L, true,
>>>> true);
>>>> +    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>> +    break;
>>>> +  }
>>>> +  case ICmpInst::ICMP_ULE: {
>>>> +    SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false, true);
>>>> +    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>> +    break;
>>>> +  }
>>>> +  case ICmpInst::ICMP_UGE: {
>>>> +    SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
>>>> +                                     SE.getNotSCEV(RHS), L, false,
>>>> true);
>>>>    if (!isa<SCEVCouldNotCompute>(TC)) return TC;
>>>>    break;
>>>>  }
>>>> @@ -2738,6 +2766,7 @@
>>>> /// executesAtLeastOnce - Test whether entry to the loop is
>>>> protected by
>>>> /// a conditional between LHS and RHS.
>>>> bool ScalarEvolutionsImpl::executesAtLeastOnce(const Loop *L, bool
>>>> isSigned,
>>>> +                                               bool trueWhenEqual,
>>>>                                               SCEV *LHS, SCEV  
>>>> *RHS) {
>>>>  BasicBlock *Preheader = L->getLoopPreheader();
>>>>  BasicBlock *PreheaderDest = L->getHeader();
>>>> @@ -2770,20 +2799,36 @@
>>>>
>>>>    switch (Cond) {
>>>>    case ICmpInst::ICMP_UGT:
>>>> -      if (isSigned) continue;
>>>> +      if (isSigned || trueWhenEqual) continue;
>>>>      std::swap(PreCondLHS, PreCondRHS);
>>>>      Cond = ICmpInst::ICMP_ULT;
>>>>      break;
>>>>    case ICmpInst::ICMP_SGT:
>>>> -      if (!isSigned) continue;
>>>> +      if (!isSigned || trueWhenEqual) continue;
>>>>      std::swap(PreCondLHS, PreCondRHS);
>>>>      Cond = ICmpInst::ICMP_SLT;
>>>>      break;
>>>>    case ICmpInst::ICMP_ULT:
>>>> -      if (isSigned) continue;
>>>> +      if (isSigned || trueWhenEqual) continue;
>>>>      break;
>>>>    case ICmpInst::ICMP_SLT:
>>>> -      if (!isSigned) continue;
>>>> +      if (!isSigned || trueWhenEqual) continue;
>>>> +      break;
>>>> +    case ICmpInst::ICMP_UGE:
>>>> +      if (isSigned || !trueWhenEqual) continue;
>>>> +      std::swap(PreCondLHS, PreCondRHS);
>>>> +      Cond = ICmpInst::ICMP_ULE;
>>>> +      break;
>>>> +    case ICmpInst::ICMP_SGE:
>>>> +      if (!isSigned || !trueWhenEqual) continue;
>>>> +      std::swap(PreCondLHS, PreCondRHS);
>>>> +      Cond = ICmpInst::ICMP_SLE;
>>>> +      break;
>>>> +    case ICmpInst::ICMP_ULE:
>>>> +      if (isSigned || !trueWhenEqual) continue;
>>>> +      break;
>>>> +    case ICmpInst::ICMP_SLE:
>>>> +      if (!isSigned || !trueWhenEqual) continue;
>>>>      break;
>>>>    default:
>>>>      continue;
>>>> @@ -2802,11 +2847,46 @@
>>>>  return false;
>>>> }
>>>>
>>>> +/// potentialInfiniteLoop - Test whether the loop might jump over
>>>> the exit value
>>>> +/// due to wrapping around 2^n.
>>>> +bool ScalarEvolutionsImpl::potentialInfiniteLoop(SCEV *Stride, SCEV
>>>> *RHS,
>>>> +                                                 bool isSigned,
>>>> bool trueWhenEqual) {
>>>> +  // Return true when the distance from RHS to maxint > Stride.
>>>> +
>>>> +  if (!isa<SCEVConstant>(Stride))
>>>> +    return true;
>>>> +  SCEVConstant *SC = cast<SCEVConstant>(Stride);
>>>> +
>>>> +  if (SC->getValue()->isZero())
>>>> +    return true;
>>>> +  if (!trueWhenEqual && SC->getValue()->isOne())
>>>> +    return false;
>>>> +
>>>> +  if (!isa<SCEVConstant>(RHS))
>>>> +    return true;
>>>> +  SCEVConstant *R = cast<SCEVConstant>(RHS);
>>>> +
>>>> +  if (isSigned)
>>>> +    return true;  // XXX: because we don't have an sdiv scev.
>>>> +
>>>> +  // If negative, it wraps around every iteration, but we don't
>>>> care about that.
>>>> +  APInt S = SC->getValue()->getValue().abs();
>>>> +
>>>> +  APInt Dist = APInt::getMaxValue(R->getValue()->getBitWidth()) -
>>>> +               R->getValue()->getValue();
>>>> +
>>>> +  if (trueWhenEqual)
>>>> +    return !S.ult(Dist);
>>>> +  else
>>>> +    return !S.ule(Dist);
>>>> +}
>>>> +
>>>> /// HowManyLessThans - Return the number of times a backedge
>>>> containing the
>>>> /// specified less-than comparison will execute.  If not computable,
>>>> return
>>>> /// UnknownValue.
>>>> SCEVHandle ScalarEvolutionsImpl::
>>>> -HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L, bool
>>>> isSigned) {
>>>> +HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
>>>> +                 bool isSigned, bool trueWhenEqual) {
>>>>  // Only handle:  "ADDREC < LoopInvariant".
>>>>  if (!RHS->isLoopInvariant(L)) return UnknownValue;
>>>>
>>>> @@ -2815,34 +2895,50 @@
>>>>    return UnknownValue;
>>>>
>>>>  if (AddRec->isAffine()) {
>>>> -    // FORNOW: We only support unit strides.
>>>> -    SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
>>>> -    if (AddRec->getOperand(1) != One)
>>>> +    SCEVHandle Stride = AddRec->getOperand(1);
>>>> +    if (potentialInfiniteLoop(Stride, RHS, isSigned,  
>>>> trueWhenEqual))
>>>>      return UnknownValue;
>>>>
>>>> -    // We know the LHS is of the form {n,+,1} and the RHS is some
>>>> loop-invariant
>>>> -    // m.  So, we count the number of iterations in which {n,+,1} <
>>>> m is true.
>>>> -    // Note that we cannot simply return max(m-n,0) because it's
>>>> not safe to
>>>> +    // We know the LHS is of the form {n,+,s} and the RHS is some
>>>> loop-invariant
>>>> +    // m.  So, we count the number of iterations in which {n,+,s} <
>>>> m is true.
>>>> +    // Note that we cannot simply return max(m-n,0)/s because it's
>>>> not safe to
>>>>    // treat m-n as signed nor unsigned due to overflow possibility.
>>>>
>>>>    // First, we get the value of the LHS in the first iteration: n
>>>>    SCEVHandle Start = AddRec->getOperand(0);
>>>>
>>>> -    if (executesAtLeastOnce(L, isSigned,
>>>> -                            SE.getMinusSCEV(AddRec->getOperand(0),
>>>> One), RHS)) {
>>>> -      // Since we know that the condition is true in order to enter
>>>> the loop,
>>>> -      // we know that it will run exactly m-n times.
>>>> -      return SE.getMinusSCEV(RHS, Start);
>>>> -    } else {
>>>> -      // Then, we get the value of the LHS in the first iteration
>>>> in which the
>>>> -      // above condition doesn't hold.  This equals to max(m,n).
>>>> -      SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start)
>>>> -                                : SE.getUMaxExpr(RHS, Start);
>>>> -
>>>> -      // Finally, we subtract these two values to get the number of
>>>> times the
>>>> -      // backedge is executed: max(m,n)-n.
>>>> -      return SE.getMinusSCEV(End, Start);
>>>> +    SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
>>>> +
>>>> +    // Assuming that the loop will run at least once, we know that
>>>> it will
>>>> +    // run (m-n)/s times.
>>>> +    SCEVHandle End = RHS;
>>>> +
>>>> +    if (!executesAtLeastOnce(L, isSigned, trueWhenEqual,
>>>> +                             SE.getMinusSCEV(Start, One), RHS)) {
>>>> +      // If not, we get the value of the LHS in the first iteration
>>>> in which
>>>> +      // the above condition doesn't hold.  This equals to  
>>>> max(m,n).
>>>> +      End = isSigned ? SE.getSMaxExpr(RHS, Start)
>>>> +                     : SE.getUMaxExpr(RHS, Start);
>>>>    }
>>>> +
>>>> +    // If the expression is less-than-or-equal to, we need to
>>>> extend the
>>>> +    // loop by one iteration.
>>>> +    //
>>>> +    // The loop won't actually run (m-n)/s times because the loop
>>>> iterations
>>>> +    // won't divide evenly. For example, if you have {2,+,5} u< 10
>>>> the
>>>> +    // division would equal one, but the loop runs twice putting  
>>>> the
>>>> +    // induction variable at 12.
>>>> +
>>>> +    if (!trueWhenEqual)
>>>> +      // (Stride - 1) is correct only because we know it's  
>>>> unsigned.
>>>> +      // What we really want is to decrease the magnitude of Stride
>>>> by one.
>>>> +      Start = SE.getMinusSCEV(Start, SE.getMinusSCEV(Stride, One));
>>>> +    else
>>>> +      Start = SE.getMinusSCEV(Start, Stride);
>>>> +
>>>> +    // Finally, we subtract these two values to get the number of
>>>> times the
>>>> +    // backedge is executed: max(m,n)-n.
>>>> +    return SE.getUDivExpr(SE.getMinusSCEV(End, Start), Stride);
>>>>  }
>>>>
>>>>  return UnknownValue;
>>>>
>>>> Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-
>>>> LessThanOrEqual.ll
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-LessThanOrEqual.ll?rev=59528&view=auto
>>>>
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> = 
>>>> = 
>>>> ====================================================================
>>>> --- llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-
>>>> LessThanOrEqual.ll (added)
>>>> +++ llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-
>>>> LessThanOrEqual.ll Tue Nov 18 09:10:54 2008
>>>> @@ -0,0 +1,31 @@
>>>> +; RUN: llvm-as < %s | opt -analyze -scalar-evolution |& \
>>>> +; RUN: grep {Loop bb: (7 + (-1 \\* %argc)) iterations!}
>>>> +
>>>> +define i32 @main(i32 %argc, i8** %argv) nounwind {
>>>> +entry:
>>>> +	%0 = icmp ugt i32 %argc, 7		; <i1> [#uses=1]
>>>> +	br i1 %0, label %bb2, label %bb.nph
>>>> +
>>>> +bb.nph:		; preds = %entry
>>>> +	br label %bb
>>>> +
>>>> +bb:		; preds = %bb.nph, %bb1
>>>> +	%indvar = phi i32 [ 0, %bb.nph ], [ %indvar.next, %bb1 ]		; <i32>
>>>> [#uses=2]
>>>> +	%argc_addr.04 = add i32 %indvar, %argc		; <i32> [#uses=1]
>>>> +	tail call void (...)* @Test() nounwind
>>>> +	%1 = add i32 %argc_addr.04, 1		; <i32> [#uses=1]
>>>> +	br label %bb1
>>>> +
>>>> +bb1:		; preds = %bb
>>>> +	%phitmp = icmp ugt i32 %1, 7		; <i1> [#uses=1]
>>>> +	%indvar.next = add i32 %indvar, 1		; <i32> [#uses=1]
>>>> +	br i1 %phitmp, label %bb1.bb2_crit_edge, label %bb
>>>> +
>>>> +bb1.bb2_crit_edge:		; preds = %bb1
>>>> +	br label %bb2
>>>> +
>>>> +bb2:		; preds = %bb1.bb2_crit_edge, %entry
>>>> +	ret i32 0
>>>> +}
>>>> +
>>>> +declare void @Test(...)
>>>>
>>>> Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18- 
>>>> Stride1.ll
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll?rev=59528&view=auto
>>>>
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> = 
>>>> = 
>>>> ====================================================================
>>>> --- llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll
>>>> (added)
>>>> +++ llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll
>>>> Tue Nov 18 09:10:54 2008
>>>> @@ -0,0 +1,30 @@
>>>> +; RUN: llvm-as < %s | opt -analyze -scalar-evolution |& grep {/u 3}
>>>> +
>>>> +define i32 @f(i32 %x) nounwind readnone {
>>>> +entry:
>>>> +	%0 = icmp ugt i32 %x, 4		; <i1> [#uses=1]
>>>> +	br i1 %0, label %bb.nph, label %bb2
>>>> +
>>>> +bb.nph:		; preds = %entry
>>>> +	br label %bb
>>>> +
>>>> +bb:		; preds = %bb.nph, %bb1
>>>> +	%indvar = phi i32 [ 0, %bb.nph ], [ %indvar.next, %bb1 ]		; <i32>
>>>> [#uses=2]
>>>> +	%tmp = mul i32 %indvar, -3		; <i32> [#uses=1]
>>>> +	%x_addr.04 = add i32 %tmp, %x		; <i32> [#uses=1]
>>>> +	%1 = add i32 %x_addr.04, -3		; <i32> [#uses=2]
>>>> +	br label %bb1
>>>> +
>>>> +bb1:		; preds = %bb
>>>> +	%2 = icmp ugt i32 %1, 4		; <i1> [#uses=1]
>>>> +	%indvar.next = add i32 %indvar, 1		; <i32> [#uses=1]
>>>> +	br i1 %2, label %bb, label %bb1.bb2_crit_edge
>>>> +
>>>> +bb1.bb2_crit_edge:		; preds = %bb1
>>>> +	%.lcssa = phi i32 [ %1, %bb1 ]		; <i32> [#uses=1]
>>>> +	br label %bb2
>>>> +
>>>> +bb2:		; preds = %bb1.bb2_crit_edge, %entry
>>>> +	%x_addr.0.lcssa = phi i32 [ %.lcssa, %bb1.bb2_crit_edge ], [ %x,
>>>> %entry ]		; <i32> [#uses=1]
>>>> +	ret i32 %x_addr.0.lcssa
>>>> +}
>>>>
>>>> Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18- 
>>>> Stride2.ll
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride2.ll?rev=59528&view=auto
>>>>
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> =
>>>> = 
>>>> = 
>>>> ====================================================================
>>>> --- llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride2.ll
>>>> (added)
>>>> +++ llvm/trunk/test/Analysis/ScalarEvolution/2008-11-18-Stride2.ll
>>>> Tue Nov 18 09:10:54 2008
>>>> @@ -0,0 +1,30 @@
>>>> +; RUN: llvm-as < %s | opt -analyze -scalar-evolution |& grep {/u 3}
>>>> +
>>>> +define i32 @f(i32 %x) nounwind readnone {
>>>> +entry:
>>>> +	%0 = icmp ugt i32 %x, 999		; <i1> [#uses=1]
>>>> +	br i1 %0, label %bb2, label %bb.nph
>>>> +
>>>> +bb.nph:		; preds = %entry
>>>> +	br label %bb
>>>> +
>>>> +bb:		; preds = %bb.nph, %bb1
>>>> +	%indvar = phi i32 [ 0, %bb.nph ], [ %indvar.next, %bb1 ]		; <i32>
>>>> [#uses=2]
>>>> +	%tmp = mul i32 %indvar, 3		; <i32> [#uses=1]
>>>> +	%x_addr.04 = add i32 %tmp, %x		; <i32> [#uses=1]
>>>> +	%1 = add i32 %x_addr.04, 3		; <i32> [#uses=2]
>>>> +	br label %bb1
>>>> +
>>>> +bb1:		; preds = %bb
>>>> +	%2 = icmp ugt i32 %1, 999		; <i1> [#uses=1]
>>>> +	%indvar.next = add i32 %indvar, 1		; <i32> [#uses=1]
>>>> +	br i1 %2, label %bb1.bb2_crit_edge, label %bb
>>>> +
>>>> +bb1.bb2_crit_edge:		; preds = %bb1
>>>> +	%.lcssa = phi i32 [ %1, %bb1 ]		; <i32> [#uses=1]
>>>> +	br label %bb2
>>>> +
>>>> +bb2:		; preds = %bb1.bb2_crit_edge, %entry
>>>> +	%x_addr.0.lcssa = phi i32 [ %.lcssa, %bb1.bb2_crit_edge ], [ %x,
>>>> %entry ]		; <i32> [#uses=1]
>>>> +	ret i32 %x_addr.0.lcssa
>>>> +}
>>>>
>>>>
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