From a95f9ed2b8348e91250a22c1aadf20637bcfcb3e Mon Sep 17 00:00:00 2001
From: Dale Johannesen <dalej@apple.com>
Date: Mon, 15 Feb 2010 23:05:03 +0000
Subject: [PATCH] More handling of DBG_VALUE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96294 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/RegAllocLocal.cpp | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/lib/CodeGen/RegAllocLocal.cpp b/lib/CodeGen/RegAllocLocal.cpp
index c25c24a67cb..04303cff5bf 100644
--- a/lib/CodeGen/RegAllocLocal.cpp
+++ b/lib/CodeGen/RegAllocLocal.cpp
@@ -490,10 +490,12 @@ MachineInstr *RALocal::reloadVirtReg(MachineBasicBlock &MBB, MachineInstr *MI,
   // If the virtual register is already available, just update the instruction
   // and return.
   if (unsigned PR = getVirt2PhysRegMapSlot(VirtReg)) {
-    MarkPhysRegRecentlyUsed(PR);       // Already have this value available!
     MI->getOperand(OpNum).setReg(PR);  // Assign the input register
-    if (!MI->isDebugValue())
+    if (!MI->isDebugValue()) {
+      // Do not do these for DBG_VALUE as they can affect codegen.
+      MarkPhysRegRecentlyUsed(PR);       // Already have this value available!
       getVirtRegLastUse(VirtReg) = std::make_pair(MI, OpNum);
+    }
     return MI;
   }
 
@@ -694,7 +696,13 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) {
     bool usedOutsideBlock = isPhysReg ? false :   
           UsedInMultipleBlocks.test(MO.getReg() -  
                                     TargetRegisterInfo::FirstVirtualRegister);
-    if (!isPhysReg && !usedOutsideBlock)
+    if (!isPhysReg && !usedOutsideBlock) {
+      // DBG_VALUE complicates this:  if the only refs of a register outside
+      // this block are DBG_VALUE, we can't keep the reg live just for that,
+      // as it will cause the reg to be spilled at the end of this block when
+      // it wouldn't have been otherwise.  Nullify the DBG_VALUEs when that
+      // happens.
+      bool UsedByDebugValueOnly = false;
       for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
            UE = MRI.reg_end(); UI != UE; ++UI)
         // Two cases:
@@ -702,12 +710,26 @@ void RALocal::ComputeLocalLiveness(MachineBasicBlock& MBB) {
         // - used in the same block before it is defined (loop)
         if (UI->getParent() != &MBB ||
             (MO.isDef() && UI.getOperand().isUse() && precedes(&*UI, MI))) {
+          if (UI->isDebugValue()) {
+            UsedByDebugValueOnly = true;
+            continue;
+          }
+          // A non-DBG_VALUE use means we can leave DBG_VALUE uses alone.
           UsedInMultipleBlocks.set(MO.getReg() - 
                                    TargetRegisterInfo::FirstVirtualRegister);
           usedOutsideBlock = true;
+          UsedByDebugValueOnly = false;
           break;
         }
-    
+      if (UsedByDebugValueOnly)
+        for (MachineRegisterInfo::reg_iterator UI = MRI.reg_begin(MO.getReg()),
+             UE = MRI.reg_end(); UI != UE; ++UI)
+          if (UI->isDebugValue() &&
+              (UI->getParent() != &MBB ||
+               (MO.isDef() && precedes(&*UI, MI))))
+            UI.getOperand().setReg(0U);
+    }
+  
     // Physical registers and those that are not live-out of the block
     // are killed/dead at their last use/def within this block.
     if (isPhysReg || !usedOutsideBlock) {