Fix PR10046 by updating LiveVariables kill info when splitting live ranges.

This only affects targets like Mips where branch instructions may kill virtual
registers. Most other targets branch on flag values, so virtual registers are
not involved.

The problem is that MachineBasicBlock::updateTerminator deletes branches and
inserts new ones while LiveVariables keeps a list of pointers to instructions
that kill virtual registers. That list wasn't properly updated in
MBB::SplitCriticalEdge.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132298 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineBasicBlock.cpp

@@ -485,6 +485,30 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
         << " -- BB#" << NMBB->getNumber()
         << " -- BB#" << Succ->getNumber() << '\n');
 
+  // On some targets like Mips, branches may kill virtual registers. Make sure
+  // that LiveVariables is properly updated after updateTerminator replaces the
+  // terminators.
+  LiveVariables *LV = P->getAnalysisIfAvailable<LiveVariables>();
+
+  // Collect a list of virtual registers killed by the terminators.
+  SmallVector<unsigned, 4> KilledRegs;
+  if (LV)
+    for (iterator I = getFirstTerminator(), E = end(); I != E; ++I) {
+      MachineInstr *MI = I;
+      for (MachineInstr::mop_iterator OI = MI->operands_begin(),
+           OE = MI->operands_end(); OI != OE; ++OI) {
+        if (!OI->isReg() || !OI->isUse() || !OI->isKill() || OI->isUndef())
+          continue;
+        unsigned Reg = OI->getReg();
+        if (TargetRegisterInfo::isVirtualRegister(Reg) &&
+            LV->getVarInfo(Reg).removeKill(MI)) {
+          KilledRegs.push_back(Reg);
+          DEBUG(dbgs() << "Removing terminator kill: " << *MI);
+          OI->setIsKill(false);
+        }
+      }
+    }
+
   ReplaceUsesOfBlockWith(Succ, NMBB);
   updateTerminator();
 
@@ -502,9 +526,22 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
       if (i->getOperand(ni+1).getMBB() == this)
         i->getOperand(ni+1).setMBB(NMBB);
 
-  if (LiveVariables *LV =
-        P->getAnalysisIfAvailable<LiveVariables>())
+  // Update LiveVariables.
+  if (LV) {
+    // Restore kills of virtual registers that were killed by the terminators.
+    while (!KilledRegs.empty()) {
+      unsigned Reg = KilledRegs.pop_back_val();
+      for (iterator I = end(), E = begin(); I != E;) {
+        if (!(--I)->addRegisterKilled(Reg, NULL, /* addIfNotFound= */ false))
+          continue;
+        LV->getVarInfo(Reg).Kills.push_back(I);
+        DEBUG(dbgs() << "Restored terminator kill: " << *I);
+        break;
+      }
+    }
+    // Update relevant live-through information.
     LV->addNewBlock(NMBB, this, Succ);
+  }
 
   if (MachineDominatorTree *MDT =
       P->getAnalysisIfAvailable<MachineDominatorTree>()) {

test/CodeGen/Mips/2011-05-26-BranchKillsVreg.ll

@@ -0,0 +1,43 @@
+; RUN: llc < %s -verify-coalescing
+; PR10046
+;
+; PHI elimination splits the critical edge from %while.end415 to %if.end427.
+; This requires updating the BNE-J terminators to a BEQ. The BNE instruction
+; kills a virtual register, and LiveVariables must be updated with the new kill
+; instruction.
+
+target datalayout = "E-p:32:32:32-i1:8:8-i8:8:32-i16:16:32-i32:32:32-i64:32:64-f32:32:32-f64:64:64-v64:64:64-n32"
+target triple = "mips-ellcc-linux"
+
+define i32 @mergesort(i8* %base, i32 %nmemb, i32 %size, i32 (i8*, i8*)* nocapture %cmp) nounwind {
+entry:
+  br i1 undef, label %return, label %if.end13
+
+if.end13:                                         ; preds = %entry
+  br label %while.body
+
+while.body:                                       ; preds = %while.body, %if.end13
+  %list1.0482 = phi i8* [ %base, %if.end13 ], [ null, %while.body ]
+  br i1 undef, label %while.end415, label %while.body
+
+while.end415:                                     ; preds = %while.body
+  br i1 undef, label %if.then419, label %if.end427
+
+if.then419:                                       ; preds = %while.end415
+  %call425 = tail call i8* @memmove(i8* %list1.0482, i8* undef, i32 undef) nounwind
+  br label %if.end427
+
+if.end427:                                        ; preds = %if.then419, %while.end415
+  %list2.1 = phi i8* [ undef, %if.then419 ], [ %list1.0482, %while.end415 ]
+  tail call void @free(i8* %list2.1)
+  unreachable
+
+return:                                           ; preds = %entry
+  ret i32 -1
+}
+
+
+declare i8* @memmove(i8*, i8*, i32)
+
+declare void @free(i8*)
+