ARM: avoid clobbering register in v6 jump-table expansion.

If we got unlucky with register allocation and actual constpool placement, we
could end up producing a tTBB_JT with an index that's already been clobbered.

Technically, we might be able to fix this situation up with a MOV, but I think
the constant islands pass is complex enough without having to deal with more
weird edge-cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297871 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MIRYamlMapping.h

@@ -381,6 +381,7 @@ struct MachineFunction {
   StringRef Name;
   unsigned Alignment = 0;
   bool ExposesReturnsTwice = false;
+  bool NoVRegs;
   // GISel MachineFunctionProperties.
   bool Legalized = false;
   bool RegBankSelected = false;
@@ -405,6 +406,7 @@ template <> struct MappingTraits<MachineFunction> {
     YamlIO.mapRequired("name", MF.Name);
     YamlIO.mapOptional("alignment", MF.Alignment);
     YamlIO.mapOptional("exposesReturnsTwice", MF.ExposesReturnsTwice);
+    YamlIO.mapOptional("noVRegs", MF.NoVRegs);
     YamlIO.mapOptional("legalized", MF.Legalized);
     YamlIO.mapOptional("regBankSelected", MF.RegBankSelected);
     YamlIO.mapOptional("selected", MF.Selected);

lib/CodeGen/MIRParser/MIRParser.cpp

@@ -332,6 +332,8 @@ bool MIRParserImpl::initializeMachineFunction(MachineFunction &MF) {
     MF.setAlignment(YamlMF.Alignment);
   MF.setExposesReturnsTwice(YamlMF.ExposesReturnsTwice);
 
+  if (YamlMF.NoVRegs)
+    MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);
   if (YamlMF.Legalized)
     MF.getProperties().set(MachineFunctionProperties::Property::Legalized);
   if (YamlMF.RegBankSelected)

lib/CodeGen/MIRPrinter.cpp

@@ -175,6 +175,8 @@ void MIRPrinter::print(const MachineFunction &MF) {
   YamlMF.Alignment = MF.getAlignment();
   YamlMF.ExposesReturnsTwice = MF.exposesReturnsTwice();
 
+  YamlMF.NoVRegs = MF.getProperties().hasProperty(
+      MachineFunctionProperties::Property::NoVRegs);
   YamlMF.Legalized = MF.getProperties().hasProperty(
       MachineFunctionProperties::Property::Legalized);
   YamlMF.RegBankSelected = MF.getProperties().hasProperty(

lib/Target/ARM/ARMConstantIslandPass.cpp

@@ -2104,6 +2104,12 @@ bool ARMConstantIslands::optimizeThumb2JumpTables() {
       IdxReg = Shift->getOperand(2).getReg();
       unsigned ShiftedIdxReg = Shift->getOperand(0).getReg();
 
+      // It's important that IdxReg is live until the actual TBB/TBH. Most of
+      // the range is checked later, but the LEA might still clobber it and not
+      // actually get removed.
+      if (BaseReg == IdxReg && !jumpTableFollowsTB(MI, User.CPEMI))
+        continue;
+
       MachineInstr *Load = User.MI->getNextNode();
       if (Load->getOpcode() != ARM::tLDRr)
         continue;
@@ -2135,14 +2141,14 @@ bool ARMConstantIslands::optimizeThumb2JumpTables() {
           // IdxReg gets redefined in the middle of the sequence.
           continue;
       }
-      
+
       // Now safe to delete the load and lsl. The LEA will be removed later.
       CanDeleteLEA = true;
       Shift->eraseFromParent();
       Load->eraseFromParent();
       DeadSize += 4;
     }
-    
+
     DEBUG(dbgs() << "Shrink JT: " << *MI);
     MachineInstr *CPEMI = User.CPEMI;
     unsigned Opc = ByteOk ? ARM::t2TBB_JT : ARM::t2TBH_JT;