[llvm] r213169 - Added documentation for SizeMultiplier in the ARM subtarget hook for register coalescing. Also fixed some 80 col violations.

[Chris Bieneman]

Author: cbieneman
Date: Wed Jul 16 11:27:31 2014
New Revision: 213169

URL: http://llvm.org/viewvc/llvm-project?rev=213169&view=rev
Log:
Added documentation for SizeMultiplier in the ARM subtarget hook for register coalescing. Also fixed some 80 col violations.

No functional code changes.

Modified:
    llvm/trunk/lib/Target/ARM/ARMSubtarget.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMSubtarget.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMSubtarget.cpp?rev=213169&r1=213168&r2=213169&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMSubtarget.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMSubtarget.cpp Wed Jul 16 11:27:31 2014
@@ -476,8 +476,17 @@ bool ARMSubtarget::shouldCoalesce(Machin
   auto AFI = MF->getInfo<ARMFunctionInfo>();
   auto It = AFI->getCoalescedWeight(MBB);
 
-  DEBUG(dbgs() << "\tARM::shouldCoalesce - Coalesced Weight: " << It->second << "\n");
-  DEBUG(dbgs() << "\tARM::shouldCoalesce - Reg Weight: " << NewRCWeight.RegWeight << "\n");
+  DEBUG(dbgs() << "\tARM::shouldCoalesce - Coalesced Weight: "
+    << It->second << "\n");
+  DEBUG(dbgs() << "\tARM::shouldCoalesce - Reg Weight: "
+    << NewRCWeight.RegWeight << "\n");
+
+  // This number is the largest round number that which meets the criteria:
+  //  (1) addresses PR18825
+  //  (2) generates better code in some test cases (like vldm-shed-a9.ll)
+  //  (3) Doesn't regress any test cases (in-tree, test-suite, and SPEC)
+  // In practice the SizeMultiplier will only factor in for straight line code
+  // that uses a lot of NEON vectors, which isn't terribly common.
   unsigned SizeMultiplier = MBB->size()/100;
   SizeMultiplier = SizeMultiplier ? SizeMultiplier : 1;
   if (It->second < NewRCWeight.WeightLimit * SizeMultiplier) {