Update comments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124843 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp
index 83706deb3f7a0a3bb5c1d85ad18ee7858901be28..04d3d311b416e7d7864f7e821a1d1516643eec49 100644 (file)
--- a/lib/CodeGen/TailDuplication.cpp
+++ b/lib/CodeGen/TailDuplication.cpp
@@ -504,8 +504,9 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
     if (!I->isPHI() && !I->isDebugValue())
       InstrCount += 1;
   }
-  // Heuristically, don't tail-duplicate calls if it would expand code size,
-  // as it's less likely to be worth the extra cost.
+  // Don't tail-duplicate calls before register allocation. Calls presents a
+  // barrier to register allocation so duplicating them may end up increasing
+  // spills.
   if (InstrCount > 1 && (PreRegAlloc && HasCall))
     return false;