Revert "Revert "[Unroll] Implement a conservative and monotonically increasing cost tracking system during the full unroll heuristic analysis that avoids counting any instruction cost until that instruction becomes "live" through a side-effect or use outside the...""

This reverts commit r269395.

Try to reapply with a fix from chapuni.

llvm-svn: 269486

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/LoopUnrollAnalyzer.cpp b/llvm/lib/Analysis/LoopUnrollAnalyzer.cpp
index fe73fe05724..a044e6bd330 100644
--- a/llvm/lib/Analysis/LoopUnrollAnalyzer.cpp
+++ b/llvm/lib/Analysis/LoopUnrollAnalyzer.cpp
@@ -189,3 +189,13 @@ bool UnrolledInstAnalyzer::visitCmpInst(CmpInst &I) {
 
   return Base::visitCmpInst(I);
 }
+
+bool UnrolledInstAnalyzer::visitPHINode(PHINode &PN) {
+  // Run base visitor first. This way we can gather some useful for later
+  // analysis information.
+  if (Base::visitPHINode(PN))
+    return true;
+
+  // The loop induction PHI nodes are definitionally free.
+  return PN.getParent() == L->getHeader();
+}