When analyzing loop exit conditions combined with and and or, don't

make any assumptions about when the two conditions will agree on when
to permit the loop to exit. This fixes PR7845.

llvm-svn: 110758

1 files changed, 12 insertions, 14 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index f5a762af825..b3ddfc032f5 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3854,14 +3854,13 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCond(const Loop *L,
         else
           MaxBECount = getUMinFromMismatchedTypes(BTI0.Max, BTI1.Max);
       } else {
-        // Both conditions must be true for the loop to exit.
+        // Both conditions must be true at the same time for the loop to exit.
+        // For now, be conservative.
         assert(L->contains(FBB) && "Loop block has no successor in loop!");
-        if (BTI0.Exact != getCouldNotCompute() &&
-            BTI1.Exact != getCouldNotCompute())
-          BECount = getUMaxFromMismatchedTypes(BTI0.Exact, BTI1.Exact);
-        if (BTI0.Max != getCouldNotCompute() &&
-            BTI1.Max != getCouldNotCompute())
-          MaxBECount = getUMaxFromMismatchedTypes(BTI0.Max, BTI1.Max);
+        if (BTI0.Max == BTI1.Max)
+          MaxBECount = BTI0.Max;
+        if (BTI0.Exact == BTI1.Exact)
+          BECount = BTI0.Exact;
       }
 
       return BackedgeTakenInfo(BECount, MaxBECount);
@@ -3889,14 +3888,13 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCond(const Loop *L,
         else
           MaxBECount = getUMinFromMismatchedTypes(BTI0.Max, BTI1.Max);
       } else {
-        // Both conditions must be false for the loop to exit.
+        // Both conditions must be false at the same time for the loop to exit.
+        // For now, be conservative.
         assert(L->contains(TBB) && "Loop block has no successor in loop!");
-        if (BTI0.Exact != getCouldNotCompute() &&
-            BTI1.Exact != getCouldNotCompute())
-          BECount = getUMaxFromMismatchedTypes(BTI0.Exact, BTI1.Exact);
-        if (BTI0.Max != getCouldNotCompute() &&
-            BTI1.Max != getCouldNotCompute())
-          MaxBECount = getUMaxFromMismatchedTypes(BTI0.Max, BTI1.Max);
+        if (BTI0.Max == BTI1.Max)
+          MaxBECount = BTI0.Max;
+        if (BTI0.Exact == BTI1.Exact)
+          BECount = BTI0.Exact;
       }
 
       return BackedgeTakenInfo(BECount, MaxBECount);