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Fix PR2002. Suppose n is the initial value for the induction
variable (with step 1) and m is its final value. Then, the correct trip count is SMAX(m,n)-n. Previously, we used SMAX(0,m-n), but m-n may overflow and can't in general be interpreted as signed. Patch by Nick Lewycky. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47007 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2527,19 +2527,17 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L, bool isSigned) {
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if (AddRec->isAffine()) {
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// The number of iterations for "{n,+,1} < m", is m-n. However, we don't
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// know that m is >= n on input to the loop. If it is, the condition
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// returns true zero times. To handle both cases, we return SMAX(0, m-n).
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// returns true zero times. To handle both cases, we return SMAX(m, n)-n.
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// FORNOW: We only support unit strides.
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SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
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if (AddRec->getOperand(1) != One)
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return UnknownValue;
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SCEVHandle Iters = SE.getMinusSCEV(RHS, AddRec->getOperand(0));
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SCEVHandle Start = AddRec->getOperand(0);
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SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start) : (SCEVHandle)RHS;
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if (isSigned)
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return SE.getSMaxExpr(SE.getIntegerSCEV(0, RHS->getType()), Iters);
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else
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return Iters;
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return SE.getMinusSCEV(End, Start);
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}
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return UnknownValue;
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16
test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.ll
Normal file
16
test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.ll
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@ -0,0 +1,16 @@
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; RUN: llvm-as < %s | opt -scalar-evolution -analyze | grep {Loop loop: ( 100 + ( -100 smax %n)) iterations!}
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; PR2002
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define void @foo(i8 %n) {
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entry:
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br label %loop
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loop:
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%i = phi i8 [ -100, %entry ], [ %i.inc, %next ]
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%cond = icmp slt i8 %i, %n
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br i1 %cond, label %next, label %return
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next:
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%i.inc = add i8 %i, 1
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br label %loop
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return:
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ret void
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}
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