[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
evan.cheng at apple.com
Wed Nov 19 09:44:04 PST 2008
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.
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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>>
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