[LoopUnrollRuntime] Use SCEV exit count for calculating trip count. NFCI

Instead of getBackEdgeTakenCount, use getExitCount on the latch exiting block
(which is proven to be the only exiting block in the loop to be unrolled).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306410 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index 5f85e17927fa2d77f9430ec4ff89ed483113c0a9..d91583136c63ce0171406d157bdfd78c5d95227c 100644 (file)
--- a/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -495,7 +495,11 @@ bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count,
 
   // Only unroll loops with a computable trip count, and the trip count needs
   // to be an int value (allowing a pointer type is a TODO item).
-  const SCEV *BECountSC = SE->getBackedgeTakenCount(L);
+  // We calculate the backedge count by using getExitCount on the Latch block,
+  // which is proven to be the only exiting block in this loop. This is same as
+  // calculating getBackedgeTakenCount on the loop (which computes SCEV for all
+  // exiting blocks).
+  const SCEV *BECountSC = SE->getExitCount(L, Latch);
   if (isa<SCEVCouldNotCompute>(BECountSC) ||
       !BECountSC->getType()->isIntegerTy())
     return false;