Fix pr6543: svn r88806 changed MachineJumpTableInfo::getJumpTableIndex() to

always create a new jump table.  The intention was to avoid merging jump
tables in SelectionDAGBuilder, and to wait for the branch folding pass to
merge tables.  Unfortunately, the same getJumpTableIndex() method is also
used to merge tables in branch folding, so as a result of this change
branch tables are never merged.  Worse, the branch folding code is expecting
getJumpTableIndex to always return the index of an existing table, but with
this change, it never does so.  In at least some cases, e.g., pr6543, this
creates references to non-existent tables.

I've fixed the problem by adding a new createJumpTableIndex function, which
will always create a new table, and I've changed getJumpTableIndex to only
look at existing tables.

llvm-svn: 98845

include/llvm/CodeGen/MachineJumpTableInfo.h

@@ -83,7 +83,11 @@ public:
   /// getEntryAlignment - Return the alignment of each entry in the jump table.
   unsigned getEntryAlignment(const TargetData &TD) const;
   
-  /// getJumpTableIndex - Create a new jump table or return an existing one.
+  /// createJumpTableIndex - Create a new jump table.
+  ///
+  unsigned createJumpTableIndex(const std::vector<MachineBasicBlock*> &DestBBs);
+  
+  /// getJumpTableIndex - Return the index for an existing jump table.
   ///
   unsigned getJumpTableIndex(const std::vector<MachineBasicBlock*> &DestBBs);
   

lib/CodeGen/MachineFunction.cpp

@@ -600,16 +600,25 @@ unsigned MachineJumpTableInfo::getEntryAlignment(const TargetData &TD) const {
   return ~0;
 }
 
-/// getJumpTableIndex - Create a new jump table entry in the jump table info
-/// or return an existing one.
+/// createJumpTableIndex - Create a new jump table entry in the jump table info.
 ///
-unsigned MachineJumpTableInfo::getJumpTableIndex(
+unsigned MachineJumpTableInfo::createJumpTableIndex(
                                const std::vector<MachineBasicBlock*> &DestBBs) {
   assert(!DestBBs.empty() && "Cannot create an empty jump table!");
   JumpTables.push_back(MachineJumpTableEntry(DestBBs));
   return JumpTables.size()-1;
 }
 
+/// getJumpTableIndex - Return the index for an existing jump table entry in
+/// the jump table info.
+unsigned MachineJumpTableInfo::getJumpTableIndex(
+                               const std::vector<MachineBasicBlock*> &DestBBs) {
+  for (unsigned i = 0, e = JumpTables.size(); i != e; ++i)
+    if (JumpTables[i].MBBs == DestBBs)
+      return i;
+  assert(false && "getJumpTableIndex failed to find matching table");
+  return ~0;
+}
 
 /// ReplaceMBBInJumpTables - If Old is the target of any jump tables, update
 /// the jump tables to branch to New instead.

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -1675,11 +1675,10 @@ bool SelectionDAGBuilder::handleJTSwitchCase(CaseRec& CR,
     }
   }
 
-  // Create a jump table index for this jump table, or return an existing
-  // one.
+  // Create a jump table index for this jump table.
   unsigned JTEncoding = TLI.getJumpTableEncoding();
   unsigned JTI = CurMF->getOrCreateJumpTableInfo(JTEncoding)
-                       ->getJumpTableIndex(DestBBs);
+                       ->createJumpTableIndex(DestBBs);
 
   // Set the jump table information so that we can codegen it as a second
   // MachineBasicBlock