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Don't try to analyze this "backward" case. This is overly conservative
pending a correct solution. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61589 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2905,6 +2905,11 @@ bool ScalarEvolutionsImpl::executesAtLeastOnce(const Loop *L, bool isSigned,
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return false;
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}
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static bool isNegative(SCEVHandle X) {
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if (SCEVConstant *C = dyn_cast<SCEVConstant>(X))
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return C->getValue()->getValue().isNegative();
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}
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/// potentialInfiniteLoop - Test whether the loop might jump over the exit value
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/// due to wrapping around 2^n.
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bool ScalarEvolutionsImpl::potentialInfiniteLoop(SCEV *Stride, SCEV *RHS,
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@ -2958,6 +2963,13 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
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if (potentialInfiniteLoop(Stride, RHS, isSigned, trueWhenEqual))
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return UnknownValue;
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// We don't handle this correctly at the moment. The problem is that when
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// the stride is negative, we're not counting how many times 'less-than' is
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// true as we approach it, we're counting how far away we are from wrapping
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// around the backside.
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if (isSigned && isNegative(Stride))
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return UnknownValue;
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// We know the LHS is of the form {n,+,s} and the RHS is some loop-invariant
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// m. So, we count the number of iterations in which {n,+,s} < m is true.
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// Note that we cannot simply return max(m-n,0)/s because it's not safe to
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@ -0,0 +1,40 @@
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; RUN: llvm-as < %s | opt -analyze -scalar-evolution | not grep {/u -1}
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; PR3275
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@g_16 = external global i16 ; <i16*> [#uses=3]
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@.str = external constant [4 x i8] ; <[4 x i8]*> [#uses=0]
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define void @func_15() nounwind {
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entry:
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%0 = load i16* @g_16, align 2 ; <i16> [#uses=1]
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%1 = icmp sgt i16 %0, 0 ; <i1> [#uses=1]
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br i1 %1, label %bb2, label %bb.nph
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bb.nph: ; preds = %entry
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%g_16.promoted = load i16* @g_16 ; <i16> [#uses=1]
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br label %bb
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bb: ; preds = %bb1, %bb.nph
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%g_16.tmp.0 = phi i16 [ %g_16.promoted, %bb.nph ], [ %2, %bb1 ] ; <i16> [#uses=1]
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%2 = add i16 %g_16.tmp.0, -1 ; <i16> [#uses=3]
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br label %bb1
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bb1: ; preds = %bb
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%3 = icmp sgt i16 %2, 0 ; <i1> [#uses=1]
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br i1 %3, label %bb1.bb2_crit_edge, label %bb
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bb1.bb2_crit_edge: ; preds = %bb1
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store i16 %2, i16* @g_16
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br label %bb2
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bb2: ; preds = %bb1.bb2_crit_edge, %entry
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br label %return
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return: ; preds = %bb2
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ret void
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}
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declare i32 @main() nounwind
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declare i32 @printf(i8*, ...) nounwind
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