[UnJ] Create a hasInvariantIterationCount function. NFC

Pulled out a separate function for some code that calculates
if an inner loop iteration count is invariant to it's outer
loop.

Differential Revision: https://reviews.llvm.org/D50063

llvm-svn: 339500

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 8e9235b..e9db472 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -1521,6 +1521,28 @@ Optional<unsigned> llvm::getLoopEstimatedTripCount(Loop *L) {
     return (FalseVal + (TrueVal / 2)) / TrueVal;
 }
 
+bool llvm::hasInvariantIterationCount(Loop *InnerLoop,
+                                      ScalarEvolution &SE) {
+  Loop *OuterL = InnerLoop->getParentLoop();
+  if (!OuterL)
+    return true;
+
+  // Get the backedge taken count for the inner loop
+  BasicBlock *InnerLoopLatch = InnerLoop->getLoopLatch();
+  const SCEV *InnerLoopBECountSC = SE.getExitCount(InnerLoop, InnerLoopLatch);
+  if (isa<SCEVCouldNotCompute>(InnerLoopBECountSC) ||
+      !InnerLoopBECountSC->getType()->isIntegerTy())
+    return false;
+
+  // Get whether count is invariant to the outer loop
+  ScalarEvolution::LoopDisposition LD =
+      SE.getLoopDisposition(InnerLoopBECountSC, OuterL);
+  if (LD != ScalarEvolution::LoopInvariant)
+    return false;
+
+  return true;
+}
+
 /// Adds a 'fast' flag to floating point operations.
 static Value *addFastMathFlag(Value *V) {
   if (isa<FPMathOperator>(V)) {