[llvm] r284152 - [RAGreedy] Empty live-ranges always succeed in last chance recoloring.

[Quentin Colombet via llvm-commits]

Author: qcolombet
Date: Thu Oct 13 14:27:48 2016
New Revision: 284152

URL: http://llvm.org/viewvc/llvm-project?rev=284152&view=rev
Log:
[RAGreedy] Empty live-ranges always succeed in last chance recoloring.

Relax the constraint for empty live-ranges while doing last chance
recoloring. Indeed, those live-ranges do not need an actual color to be
fond for the recoloring to work.
Empty live-range may happen as a result of splitting/spilling.

Unfortunately no test case for in-tree targets.

Modified:
    llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp

Modified: llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp?rev=284152&r1=284151&r2=284152&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp Thu Oct 13 14:27:48 2016
@@ -2223,10 +2223,21 @@ bool RAGreedy::tryRecoloringCandidates(P
     DEBUG(dbgs() << "Try to recolor: " << *LI << '\n');
     unsigned PhysReg;
     PhysReg = selectOrSplitImpl(*LI, NewVRegs, FixedRegisters, Depth + 1);
-    if (PhysReg == ~0u || !PhysReg)
+    // When splitting happens, the live-range may actually be empty.
+    // In that case, this is okay to continue the recoloring even
+    // if we did not find an alternative color for it. Indeed,
+    // there will not be anything to color for LI in the end.
+    if (PhysReg == ~0u || (!PhysReg && !LI->empty()))
       return false;
+
+    if (!PhysReg) {
+      assert(LI->empty() && "Only empty live-range do not require a register");
+      DEBUG(dbgs() << "Recoloring of " << *LI << " succeeded. Empty LI.\n");
+      continue;
+    }
     DEBUG(dbgs() << "Recoloring of " << *LI
                  << " succeeded with: " << PrintReg(PhysReg, TRI) << '\n');
+
     Matrix->assign(*LI, PhysReg);
     FixedRegisters.insert(LI->reg);
   }