From eefdebe002ede066bf80859e72aec831cfd1d92d Mon Sep 17 00:00:00 2001 From: Nick Lewycky Date: Mon, 16 Jul 2007 02:08:00 +0000 Subject: [PATCH] Handle decrementing loops properly. Fixes PR1533. Always pass the constant as the second parameter to HowManyLessThans. Remove obsolete "isSigned" parameter. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39893 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../Analysis/ScalarEvolutionExpressions.h | 6 ++-- lib/Analysis/ScalarEvolution.cpp | 28 +++++++++---------- .../2007-07-15-NegativeStride.ll | 20 +++++++++++++ 3 files changed, 35 insertions(+), 19 deletions(-) create mode 100644 test/Analysis/ScalarEvolution/2007-07-15-NegativeStride.ll diff --git a/include/llvm/Analysis/ScalarEvolutionExpressions.h b/include/llvm/Analysis/ScalarEvolutionExpressions.h index 957ddadcb51..af1656ee8ea 100644 --- a/include/llvm/Analysis/ScalarEvolutionExpressions.h +++ b/include/llvm/Analysis/ScalarEvolutionExpressions.h @@ -475,10 +475,8 @@ namespace llvm { /// looking at this is that it returns the first iteration number where the /// value is not in the condition, thus computing the exit count. If the /// iteration count can't be computed, an instance of SCEVCouldNotCompute is - /// returned. The isSigned parameter indicates whether the ConstantRange - /// should be treated as signed or unsigned. - SCEVHandle getNumIterationsInRange(ConstantRange Range, - bool isSigned) const; + /// returned. + SCEVHandle getNumIterationsInRange(ConstantRange Range) const; SCEVHandle replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym, const SCEVHandle &Conc) const; diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index 1c56c1f995e..0039144d897 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -1671,8 +1671,7 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) { ConstantRange CompRange( ICmpInst::makeConstantRange(Cond, CompVal->getValue())); - SCEVHandle Ret = AddRec->getNumIterationsInRange(CompRange, - false /*Always treat as unsigned range*/); + SCEVHandle Ret = AddRec->getNumIterationsInRange(CompRange); if (!isa(Ret)) return Ret; } } @@ -1696,7 +1695,8 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) { break; } case ICmpInst::ICMP_SGT: { - SCEVHandle TC = HowManyLessThans(RHS, LHS, L); + SCEVHandle TC = HowManyLessThans(SCEV::getNegativeSCEV(LHS), + SCEV::getNegativeSCEV(RHS), L); if (!isa(TC)) return TC; break; } @@ -2406,8 +2406,7 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L) { /// this is that it returns the first iteration number where the value is not in /// the condition, thus computing the exit count. If the iteration count can't /// be computed, an instance of SCEVCouldNotCompute is returned. -SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range, - bool isSigned) const { +SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range) const { if (Range.isFullSet()) // Infinite loop. return new SCEVCouldNotCompute(); @@ -2419,7 +2418,7 @@ SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range, SCEVHandle Shifted = SCEVAddRecExpr::get(Operands, getLoop()); if (SCEVAddRecExpr *ShiftedAddRec = dyn_cast(Shifted)) return ShiftedAddRec->getNumIterationsInRange( - Range.subtract(SC->getValue()->getValue()),isSigned); + Range.subtract(SC->getValue()->getValue())); // This is strange and shouldn't happen. return new SCEVCouldNotCompute(); } @@ -2443,17 +2442,16 @@ SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range, // If this is an affine expression then we have this situation: // Solve {0,+,A} in Range === Ax in Range - // Since we know that zero is in the range, we know that the upper value of - // the range must be the first possible exit value. Also note that we - // already checked for a full range. - const APInt &Upper = Range.getUpper(); - APInt A = cast(getOperand(1))->getValue()->getValue(); + // We know that zero is in the range. If A is positive then we know that + // the upper value of the range must be the first possible exit value. + // If A is negative then the lower of the range is the last possible loop + // value. Also note that we already checked for a full range. APInt One(getBitWidth(),1); + APInt A = cast(getOperand(1))->getValue()->getValue(); + APInt End = A.sge(One) ? (Range.getUpper() - One) : Range.getLower(); - // The exit value should be (Upper+A-1)/A. - APInt ExitVal(Upper); - if (A != One) - ExitVal = (Upper + A - One).sdiv(A); + // The exit value should be (End+A)/A. + APInt ExitVal = (End + A).sdiv(A); ConstantInt *ExitValue = ConstantInt::get(ExitVal); // Evaluate at the exit value. If we really did fall out of the valid diff --git a/test/Analysis/ScalarEvolution/2007-07-15-NegativeStride.ll b/test/Analysis/ScalarEvolution/2007-07-15-NegativeStride.ll new file mode 100644 index 00000000000..ef5cd2f8a32 --- /dev/null +++ b/test/Analysis/ScalarEvolution/2007-07-15-NegativeStride.ll @@ -0,0 +1,20 @@ +; RUN: llvm-as < %s | opt -analyze -scalar-evolution 2>&1 | grep "Loop bb: 100 iterations" +; PR1533 + +@array = weak global [101 x i32] zeroinitializer, align 32 ; <[100 x i32]*> [#uses=1] + +define void @loop(i32 %x) { +entry: + br label %bb + +bb: ; preds = %bb, %entry + %i.01.0 = phi i32 [ 100, %entry ], [ %tmp4, %bb ] ; [#uses=2] + %tmp1 = getelementptr [101 x i32]* @array, i32 0, i32 %i.01.0 ; [#uses=1] + store i32 %x, i32* %tmp1 + %tmp4 = add i32 %i.01.0, -1 ; [#uses=2] + %tmp7 = icmp sgt i32 %tmp4, -1 ; [#uses=1] + br i1 %tmp7, label %bb, label %return + +return: ; preds = %bb + ret void +}