[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
Evan Cheng
echeng at apple.com
Thu Nov 20 08:54:32 PST 2008
Ah ok. Thanks.
Evan
On Nov 19, 2008, at 8:41 PM, Nick Lewycky wrote:
> 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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