From 3d7d0bc71a858bdd251a84f7a58a379894afe118 Mon Sep 17 00:00:00 2001 From: Manman Ren Date: Wed, 26 Mar 2014 22:14:09 +0000 Subject: Add comments. Addressing review comments from Evan on r204690. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204864 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/RegAllocGreedy.cpp | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'lib/CodeGen/RegAllocGreedy.cpp') diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp index 3a4ad620d0..a4f6b682a2 100644 --- a/lib/CodeGen/RegAllocGreedy.cpp +++ b/lib/CodeGen/RegAllocGreedy.cpp @@ -2122,6 +2122,11 @@ unsigned RAGreedy::selectOrSplitImpl(LiveInterval &VirtReg, CSRFirstUse = true; BlockFrequency CSRCost(CSRFirstTimeCost); + // Using a CSR for the first time has a cost because it causes push|pop + // to be added to prologue|epilogue. Splitting a cold section of the live + // range can have lower cost than using the CSR for the first time; + // Spilling a live range in the cold path can have lower cost than using + // the CSR for the first time. if (getStage(VirtReg) == RS_Spill && CSRFirstUse && NewVRegs.empty() && CSRFirstTimeCost > 0 && VirtReg.isSpillable()) { // We choose spill over using the CSR for the first time if the spill cost -- cgit v1.2.3