Rearrange handling of jump tables. Highlights:

1. MachineJumpTableInfo is now created lazily for a function the first time
   it actually makes a jump table instead of for every function.
2. The encoding of jump table entries is now described by the
   MachineJumpTableInfo::JTEntryKind enum.  This enum is determined by the
   TLI::getJumpTableEncoding() hook, instead of by lots of code scattered
   throughout the compiler that "knows" that jump table entries are always
   32-bits in pic mode (for example).
3. The size and alignment of jump table entries is now calculated based on
   their kind, instead of at machinefunction creation time.

Future work includes using the EntryKind in more places in the compiler,
eliminating other logic that "knows" the layout of jump tables in various
situations.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94470 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 49 insertions, 44 deletions

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 92849d31e5..4f76aac279 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -206,53 +206,56 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF,
   // See if any jump tables have become mergable or dead as the code generator
   // did its thing.
   MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
+  if (JTI == 0) {
+    delete RS;
+    return MadeChange;
+  }
+  
   const std::vector<MachineJumpTableEntry> &JTs = JTI->getJumpTables();
-  if (!JTs.empty()) {
-    // Figure out how these jump tables should be merged.
-    std::vector<unsigned> JTMapping;
-    JTMapping.reserve(JTs.size());
-
-    // We always keep the 0th jump table.
-    JTMapping.push_back(0);
-
-    // Scan the jump tables, seeing if there are any duplicates.  Note that this
-    // is N^2, which should be fixed someday.
-    for (unsigned i = 1, e = JTs.size(); i != e; ++i) {
-      if (JTs[i].MBBs.empty())
-        JTMapping.push_back(i);
-      else
-        JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs));
-    }
-
-    // If a jump table was merge with another one, walk the function rewriting
-    // references to jump tables to reference the new JT ID's.  Keep track of
-    // whether we see a jump table idx, if not, we can delete the JT.
-    BitVector JTIsLive(JTs.size());
-    for (MachineFunction::iterator BB = MF.begin(), E = MF.end();
-         BB != E; ++BB) {
-      for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
-           I != E; ++I)
-        for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) {
-          MachineOperand &Op = I->getOperand(op);
-          if (!Op.isJTI()) continue;
-          unsigned NewIdx = JTMapping[Op.getIndex()];
-          Op.setIndex(NewIdx);
-
-          // Remember that this JT is live.
-          JTIsLive.set(NewIdx);
-        }
-    }
+  // Figure out how these jump tables should be merged.
+  std::vector<unsigned> JTMapping;
+  JTMapping.reserve(JTs.size());
+
+  // We always keep the 0th jump table.
+  JTMapping.push_back(0);
+
+  // Scan the jump tables, seeing if there are any duplicates.  Note that this
+  // is N^2, which should be fixed someday.
+  for (unsigned i = 1, e = JTs.size(); i != e; ++i) {
+    if (JTs[i].MBBs.empty())
+      JTMapping.push_back(i);
+    else
+      JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs));
+  }
 
-    // Finally, remove dead jump tables.  This happens either because the
-    // indirect jump was unreachable (and thus deleted) or because the jump
-    // table was merged with some other one.
-    for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
-      if (!JTIsLive.test(i)) {
-        JTI->RemoveJumpTable(i);
-        MadeChange = true;
+  // If a jump table was merge with another one, walk the function rewriting
+  // references to jump tables to reference the new JT ID's.  Keep track of
+  // whether we see a jump table idx, if not, we can delete the JT.
+  BitVector JTIsLive(JTs.size());
+  for (MachineFunction::iterator BB = MF.begin(), E = MF.end();
+       BB != E; ++BB) {
+    for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
+         I != E; ++I)
+      for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) {
+        MachineOperand &Op = I->getOperand(op);
+        if (!Op.isJTI()) continue;
+        unsigned NewIdx = JTMapping[Op.getIndex()];
+        Op.setIndex(NewIdx);
+
+        // Remember that this JT is live.
+        JTIsLive.set(NewIdx);
       }
   }
 
+  // Finally, remove dead jump tables.  This happens either because the
+  // indirect jump was unreachable (and thus deleted) or because the jump
+  // table was merged with some other one.
+  for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
+    if (!JTIsLive.test(i)) {
+      JTI->RemoveJumpTable(i);
+      MadeChange = true;
+    }
+
   delete RS;
   return MadeChange;
 }
@@ -957,7 +960,8 @@ ReoptimizeBlock:
       }
       // If MBB was the target of a jump table, update jump tables to go to the
       // fallthrough instead.
-      MF.getJumpTableInfo()->ReplaceMBBInJumpTables(MBB, FallThrough);
+      if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
+        MJTI->ReplaceMBBInJumpTables(MBB, FallThrough);
       MadeChange = true;
     }
     return MadeChange;
@@ -1191,7 +1195,8 @@ ReoptimizeBlock:
           }
 
           // Change any jumptables to go to the new MBB.
-          MF.getJumpTableInfo()->ReplaceMBBInJumpTables(MBB, CurTBB);
+          if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
+            MJTI->ReplaceMBBInJumpTables(MBB, CurTBB);
           if (DidChange) {
             ++NumBranchOpts;
             MadeChange = true;