LSR: Fix the parameters used to compute the scaling factor cost.

Prior to this change, the considered addressing modes may be invalid since the
maximum and minimum offsets were not taking into account.
This was causing an assertion failure.

The added test case exercices that behavior.

<rdar://problem/14199725> Assertion failed: (CurScaleCost >= 0 && "Legal
addressing mode has an illegal cost!")

llvm-svn: 184341

1 files changed, 13 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 246de56d9ad..14cb9793925 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1417,11 +1417,19 @@ static unsigned getScalingFactorCost(const TargetTransformInfo &TTI,
 
   switch (LU.Kind) {
   case LSRUse::Address: {
-    int CurScaleCost = TTI.getScalingFactorCost(LU.AccessTy, F.BaseGV,
-                                                F.BaseOffset, F.HasBaseReg,
-                                                F.Scale);
-    assert(CurScaleCost >= 0 && "Legal addressing mode has an illegal cost!");
-    return CurScaleCost;
+    // Check the scaling factor cost with both the min and max offsets.
+    int ScaleCostMinOffset =
+      TTI.getScalingFactorCost(LU.AccessTy, F.BaseGV,
+                               F.BaseOffset + LU.MinOffset,
+                               F.HasBaseReg, F.Scale);
+    int ScaleCostMaxOffset =
+      TTI.getScalingFactorCost(LU.AccessTy, F.BaseGV,
+                               F.BaseOffset + LU.MaxOffset,
+                               F.HasBaseReg, F.Scale);
+
+    assert(ScaleCostMinOffset >= 0 && ScaleCostMaxOffset >= 0 &&
+           "Legal addressing mode has an illegal cost!");
+    return std::max(ScaleCostMinOffset, ScaleCostMaxOffset);
   }
   case LSRUse::ICmpZero:
     // ICmpZero BaseReg + -1*ScaleReg => ICmp BaseReg, ScaleReg.