From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 15 Nov 2006 20:54:11 +0000 (+0000)
Subject: A register def can be partially dead when the whole register has use(s) but a subreg... 
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=9a1956ae6ad2d4892afbc9f1b97d645d220b6d4a;hp=a6c4c1eb90413986519c46f70222539dee39ffe9;p=oota-llvm.git

A register def can be partially dead when the whole register has use(s) but a subreg does not.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31760 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 730ad239141..03f38602aee 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -575,7 +575,6 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
   // A physical register cannot be live across basic block, so its
   // lifetime must end somewhere in its defining basic block.
   DEBUG(std::cerr << "\t\tregister: "; printRegName(interval.reg));
-  typedef LiveVariables::killed_iterator KillIter;
 
   unsigned baseIndex = MIIdx;
   unsigned start = getDefIndex(baseIndex);
@@ -599,6 +598,14 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
       DEBUG(std::cerr << " killed");
       end = getUseIndex(baseIndex) + 1;
       goto exit;
+    } else if (lv_->ModifiesRegister(mi, interval.reg)) {
+      // Another instruction redefines the register before it is ever read.
+      // Then the register is essentially dead at the instruction that defines
+      // it. Hence its interval is:
+      // [defSlot(def), defSlot(def)+1)
+      DEBUG(std::cerr << " dead");
+      end = getDefIndex(start) + 1;
+      goto exit;
     }
   }