[LV] Introduce TTI::getMinimumVF

The function getMinimumVF(ElemWidth) will return the minimum VF for
a vector with elements of size ElemWidth bits. This value will only
apply to targets for which TTI::shouldMaximizeVectorBandwidth returns
true. The value of 0 indicates that there is no minimum VF.

Differential Revision: https://reviews.llvm.org/D45271

llvm-svn: 330062

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 51be86f..fa73661 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6143,6 +6143,13 @@ LoopVectorizationCostModel::computeFeasibleMaxVF(bool OptForSize,
         break;
       }
     }
+    if (unsigned MinVF = TTI.getMinimumVF(SmallestType)) {
+      if (MaxVF < MinVF) {
+        DEBUG(dbgs() << "LV: Overriding calculated MaxVF(" << MaxVF
+                     << ") with target's minimum: " << MinVF << '\n');
+        MaxVF = MinVF;
+      }
+    }
   }
   return MaxVF;
 }