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| author | Nick Lewycky <nicholas@mxc.ca> | 2011-09-05 23:25:16 +0000 |
|---|---|---|
| committer | Nick Lewycky <nicholas@mxc.ca> | 2011-09-05 23:25:16 +0000 |
| commit | 77b7352db027cb486d25a92c2756c379a3073d7f (patch) | |
| tree | 37abbda921f303171f556c95b34bb734a62fa18d /lib/Analysis | |
| parent | 1fac6b50ea720d75fc2bf01a288e99f239869e90 (diff) | |
| download | llvm-77b7352db027cb486d25a92c2756c379a3073d7f.tar.gz llvm-77b7352db027cb486d25a92c2756c379a3073d7f.tar.bz2 llvm-77b7352db027cb486d25a92c2756c379a3073d7f.tar.xz | |
Teach SCEV to report a max backedge count in one interesting case in
HowFarToZero; the case for a canonical loop.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139126 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis')
| -rw-r--r-- | lib/Analysis/ScalarEvolution.cpp | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index 8859c3b22f..a2cd38b4bf 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -5184,8 +5184,12 @@ ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L) { // Handle unitary steps, which cannot wraparound. // 1*N = -Start; -1*N = Start (mod 2^BW), so: // N = Distance (as unsigned) - if (StepC->getValue()->equalsInt(1) || StepC->getValue()->isAllOnesValue()) - return Distance; + if (StepC->getValue()->equalsInt(1) || StepC->getValue()->isAllOnesValue()) { + ConstantRange CR = getUnsignedRange(Start); + const SCEV *MaxBECount = getConstant(CountDown ? CR.getUnsignedMax() + : ~CR.getUnsignedMin()); + return ExitLimit(Distance, MaxBECount); + } // If the recurrence is known not to wraparound, unsigned divide computes the // back edge count. We know that the value will either become zero (and thus |