After r147827 and r147902, it's now possible for unallocatable registers to be

live across BBs before register allocation. This miscompiled 197.parser
when a cmp + b are optimized to a cbnz instruction even though the CPSR def
is live-in a successor.
        cbnz    r6, LBB89_12
...
LBB89_12:
        ble     LBB89_1

The fix consists of two parts. 1) Teach LiveVariables that some unallocatable
registers might be liveouts so don't mark their last use as kill if they are.
2) ARM constantpool island pass shouldn't form cbz / cbnz if the conditional
branch does not kill CPSR.

rdar://10676853


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148168 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 6 deletions

diff --git a/lib/CodeGen/LiveVariables.cpp b/lib/CodeGen/LiveVariables.cpp
index 7477d91930..96d36c8e56 100644
--- a/lib/CodeGen/LiveVariables.cpp
+++ b/lib/CodeGen/LiveVariables.cpp
@@ -261,12 +261,11 @@ void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr *MI) {
           Processed.insert(*SS);
       }
     }
-  }
-  else if (LastDef && !PhysRegUse[Reg] &&
-           !LastDef->findRegisterDefOperand(Reg))
+  } else if (LastDef && !PhysRegUse[Reg] &&
+             !LastDef->findRegisterDefOperand(Reg))
     // Last def defines the super register, add an implicit def of reg.
-    LastDef->addOperand(MachineOperand::CreateReg(Reg,
-                                                 true/*IsDef*/, true/*IsImp*/));
+    LastDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
+                                                  true/*IsImp*/));
 
   // Remember this use.
   PhysRegUse[Reg]  = MI;
@@ -607,10 +606,27 @@ bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
       }
     }
 
+    // MachineCSE may CSE instructions which write to non-allocatable physical
+    // registers across MBBs. Remember if any reserved register is liveout.
+    SmallSet<unsigned, 4> LiveOuts;
+    for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
+           SE = MBB->succ_end(); SI != SE; ++SI) {
+      MachineBasicBlock *SuccMBB = *SI;
+      if (SuccMBB->isLandingPad())
+        continue;
+      for (MachineBasicBlock::livein_iterator LI = SuccMBB->livein_begin(),
+             LE = SuccMBB->livein_end(); LI != LE; ++LI) {
+        unsigned LReg = *LI;
+        if (!TRI->isInAllocatableClass(LReg))
+          // Ignore other live-ins, e.g. those that are live into landing pads.
+          LiveOuts.insert(LReg);
+      }
+    }
+
     // Loop over PhysRegDef / PhysRegUse, killing any registers that are
     // available at the end of the basic block.
     for (unsigned i = 0; i != NumRegs; ++i)
-      if (PhysRegDef[i] || PhysRegUse[i])
+      if ((PhysRegDef[i] || PhysRegUse[i]) && !LiveOuts.count(i))
         HandlePhysRegDef(i, 0, Defs);
 
     std::fill(PhysRegDef,  PhysRegDef  + NumRegs, (MachineInstr*)0);