1 files changed, 6 insertions, 1 deletions
diff --git a/lib/Transforms/Scalar/LoopUnrollPass.cpp b/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 7da2b52da5..99a38b1ed0 100644
--- a/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -158,7 +158,12 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
       DEBUG(dbgs() << "  Not unrolling loop with inlinable calls.\n");
       return false;
     }
-    uint64_t Size = (uint64_t)LoopSize*Count;
+    
+    // NOTE: We multiply by the loop depth because unrolling inner loops of
+    // very deep nests tends to result in high register pressure, which we don't
+    // currently recover from very well.  When and if the register allocator/
+    // spiller improves to compensate, this should be re-evaluated.
+    uint64_t Size = (uint64_t)LoopSize*Count*L->getLoopDepth();
     if (TripCount != 1 && Size > CurrentThreshold) {
       DEBUG(dbgs() << "  Too large to fully unroll with count: " << Count
             << " because size: " << Size << ">" << CurrentThreshold << "\n");