Fix PR3243: a LiveVariables bug. When HandlePhysRegKill is checking whether the last reference is also the last def (i.e. dead def), it should also check if last reference is the current machine instruction being processed. This can happen when it is processing a physical register use and setting the current machine instruction as sub-register's last ref.

llvm-svn: 62617

1 files changed, 15 insertions, 13 deletions

diff --git a/llvm/lib/CodeGen/LiveVariables.cpp b/llvm/lib/CodeGen/LiveVariables.cpp
index ecfebc5..a7bdbd9 100644
--- a/llvm/lib/CodeGen/LiveVariables.cpp
+++ b/llvm/lib/CodeGen/LiveVariables.cpp
@@ -335,7 +335,7 @@ bool LiveVariables::hasRegisterUseBelow(unsigned Reg,
   return true;
 }
 
-bool LiveVariables::HandlePhysRegKill(unsigned Reg) {
+bool LiveVariables::HandlePhysRegKill(unsigned Reg, MachineInstr *MI) {
   if (!PhysRegUse[Reg] && !PhysRegDef[Reg])
     return false;
 
@@ -373,8 +373,10 @@ bool LiveVariables::HandlePhysRegKill(unsigned Reg) {
       }
     }
   }
-  if (LastRefOrPartRef == PhysRegDef[Reg])
-    // Not used at all.
+
+  if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI)
+    // If the last reference is the last def, then it's not used at all.
+    // That is, unless we are currently processing the last reference itself.
     LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
 
   /* Partial uses. Mark register def dead and add implicit def of
@@ -427,14 +429,14 @@ void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) {
 
   // Start from the largest piece, find the last time any part of the register
   // is referenced.
-  if (!HandlePhysRegKill(Reg)) {
+  if (!HandlePhysRegKill(Reg, MI)) {
     // Only some of the sub-registers are used.
     for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
          unsigned SubReg = *SubRegs; ++SubRegs) {
       if (!Live.count(SubReg))
         // Skip if this sub-register isn't defined.
         continue;
-      if (HandlePhysRegKill(SubReg)) {
+      if (HandlePhysRegKill(SubReg, MI)) {
         Live.erase(SubReg);
         for (const unsigned *SS = TRI->getSubRegisters(SubReg); *SS; ++SS)
           Live.erase(*SS);
@@ -475,7 +477,7 @@ void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) {
           }
         } else {
           // Otherwise, the super register is killed.
-          if (HandlePhysRegKill(SuperReg)) {
+          if (HandlePhysRegKill(SuperReg, MI)) {
             PhysRegDef[SuperReg]  = NULL;
             PhysRegUse[SuperReg]  = NULL;
             for (const unsigned *SS = TRI->getSubRegisters(SuperReg); *SS; ++SS) {
@@ -558,13 +560,13 @@ bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
       SmallVector<unsigned, 4> DefRegs;
       for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
         const MachineOperand &MO = MI->getOperand(i);
-        if (MO.isReg() && MO.getReg()) {
-          unsigned MOReg = MO.getReg();
-          if (MO.isUse())
-            UseRegs.push_back(MOReg);
-          if (MO.isDef())
-            DefRegs.push_back(MOReg);
-        }
+        if (!MO.isReg() || MO.getReg() == 0)
+          continue;
+        unsigned MOReg = MO.getReg();
+        if (MO.isUse())
+          UseRegs.push_back(MOReg);
+        if (MO.isDef())
+          DefRegs.push_back(MOReg);
       }
 
       // Process all uses.