[MachineOutliner][NFC] Only map blocks which have adjacent legal instructions

If a block doesn't have any ranges of adjacent legal instructions, then it
can't have outlining candidates. There's no point in mapping legal isntructions
in situations like this.

I noticed this reduces the size of the suffix tree in sqlite3 for AArch64 at
-Oz by about 3%.

llvm-svn: 346379

lib/CodeGen/MachineOutliner.cpp

@@ -640,18 +640,26 @@ struct InstructionMapper {
 
   /// Maps \p *It to a legal integer.
   ///
-  /// Updates \p InstrListForMBB, \p UnsignedVecForMBB, \p
-  /// InstructionIntegerMap, \p IntegerInstructionMap, and \p LegalInstrNumber.
+  /// Updates \p CanOutlineWithPrevInstr, \p HaveLegalRange, \p InstrListForMBB,
+  /// \p UnsignedVecForMBB, \p InstructionIntegerMap, \p IntegerInstructionMap,
+  /// and \p LegalInstrNumber.
   ///
   /// \returns The integer that \p *It was mapped to.
   unsigned mapToLegalUnsigned(
-      MachineBasicBlock::iterator &It, unsigned &NumLegalInBlock,
+      MachineBasicBlock::iterator &It, bool &CanOutlineWithPrevInstr,
+      bool &HaveLegalRange, unsigned &NumLegalInBlock,
       std::vector<unsigned> &UnsignedVecForMBB,
       std::vector<MachineBasicBlock::iterator> &InstrListForMBB) {
     // We added something legal, so we should unset the AddedLegalLastTime
     // flag.
     AddedIllegalLastTime = false;
 
+    // If we have at least two adjacent legal instructions (which may have
+    // invisible instructions in between), remember that.
+    if (CanOutlineWithPrevInstr)
+      HaveLegalRange = true;
+    CanOutlineWithPrevInstr = true;
+
     // Keep track of the number of legal instructions we insert.
     NumLegalInBlock++;
 
@@ -692,9 +700,12 @@ struct InstructionMapper {
   /// IllegalInstrNumber.
   ///
   /// \returns The integer that \p *It was mapped to.
-  unsigned mapToIllegalUnsigned(
-      MachineBasicBlock::iterator &It, std::vector<unsigned> &UnsignedVecForMBB,
-      std::vector<MachineBasicBlock::iterator> &InstrListForMBB) {
+  unsigned mapToIllegalUnsigned(MachineBasicBlock::iterator &It,
+  bool &CanOutlineWithPrevInstr, std::vector<unsigned> &UnsignedVecForMBB,
+  std::vector<MachineBasicBlock::iterator> &InstrListForMBB) {
+    // Can't outline an illegal instruction. Set the flag.
+    CanOutlineWithPrevInstr = false;
+
     // Only add one illegal number per range of legal numbers.
     if (AddedIllegalLastTime)
       return IllegalInstrNumber;
@@ -738,6 +749,14 @@ struct InstructionMapper {
     // outlining.
     unsigned NumLegalInBlock = 0;
 
+    // True if we have at least two legal instructions which aren't separated
+    // by an illegal instruction.
+    bool HaveLegalRange = false;
+
+    // True if we can perform outlining given the last mapped (non-invisible)
+    // instruction. This lets us know if we have a legal range.
+    bool CanOutlineWithPrevInstr = false;
+
     // FIXME: Should this all just be handled in the target, rather than using
     // repeated calls to getOutliningType?
     std::vector<unsigned> UnsignedVecForMBB;
@@ -747,20 +766,22 @@ struct InstructionMapper {
       // Keep track of where this instruction is in the module.
       switch (TII.getOutliningType(It, Flags)) {
       case InstrType::Illegal:
-        mapToIllegalUnsigned(It, UnsignedVecForMBB, InstrListForMBB);
+        mapToIllegalUnsigned(It, CanOutlineWithPrevInstr,
+                             UnsignedVecForMBB, InstrListForMBB);
         break;
 
       case InstrType::Legal:
-        mapToLegalUnsigned(It, NumLegalInBlock, UnsignedVecForMBB,
-                           InstrListForMBB);
+        mapToLegalUnsigned(It, CanOutlineWithPrevInstr, HaveLegalRange,
+                           NumLegalInBlock, UnsignedVecForMBB, InstrListForMBB);
         break;
 
       case InstrType::LegalTerminator:
-        mapToLegalUnsigned(It, NumLegalInBlock, UnsignedVecForMBB,
-                           InstrListForMBB);
+        mapToLegalUnsigned(It, CanOutlineWithPrevInstr, HaveLegalRange,
+                           NumLegalInBlock, UnsignedVecForMBB, InstrListForMBB);
         // The instruction also acts as a terminator, so we have to record that
         // in the string.
-        mapToIllegalUnsigned(It, UnsignedVecForMBB, InstrListForMBB);
+        mapToIllegalUnsigned(It, CanOutlineWithPrevInstr, UnsignedVecForMBB,
+        InstrListForMBB);
         break;
 
       case InstrType::Invisible:
@@ -773,12 +794,13 @@ struct InstructionMapper {
 
     // Are there enough legal instructions in the block for outlining to be
     // possible?
-    if (NumLegalInBlock > 1) {
+    if (HaveLegalRange) {
       // After we're done every insertion, uniquely terminate this part of the
       // "string". This makes sure we won't match across basic block or function
       // boundaries since the "end" is encoded uniquely and thus appears in no
       // repeated substring.
-      mapToIllegalUnsigned(It, UnsignedVecForMBB, InstrListForMBB);
+      mapToIllegalUnsigned(It, CanOutlineWithPrevInstr, UnsignedVecForMBB,
+      InstrListForMBB);
       InstrList.insert(InstrList.end(), InstrListForMBB.begin(),
                        InstrListForMBB.end());
       UnsignedVec.insert(UnsignedVec.end(), UnsignedVecForMBB.begin(),