Add target hook for pseudo instruction expansion.

Many targets use pseudo instructions to help register allocation.  Like
the COPY instruction, these pseudos can be expanded after register
allocation.  The early expansion can make life easier for PEI and the
post-ra scheduler.

This patch adds a hook that is called for all remaining pseudo
instructions from the ExpandPostRAPseudos pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140472 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 35 insertions, 7 deletions

diff --git a/include/llvm/MC/MCInstrDesc.h b/include/llvm/MC/MCInstrDesc.h
index 7061fcb..aafa800 100644
--- a/include/llvm/MC/MCInstrDesc.h
+++ b/include/llvm/MC/MCInstrDesc.h
@@ -97,6 +97,7 @@ namespace MCID {
   enum {
     Variadic = 0,
     HasOptionalDef,
+    Pseudo,
     Return,
     Call,
     Barrier,
@@ -275,6 +276,13 @@ public:
     return Size;
   }
 
+  /// isPseudo - Return true if this is a pseudo instruction that doesn't
+  /// correspond to a real machine instruction.
+  ///
+  bool isPseudo() const {
+    return Flags & (1 << MCID::Pseudo);
+  }
+
   bool isReturn() const {
     return Flags & (1 << MCID::Return);
   }
diff --git a/include/llvm/Target/TargetInstrInfo.h b/include/llvm/Target/TargetInstrInfo.h
index e6e963c..bbe5897 100644
--- a/include/llvm/Target/TargetInstrInfo.h
+++ b/include/llvm/Target/TargetInstrInfo.h
@@ -386,6 +386,16 @@ public:
   assert(0 && "Target didn't implement TargetInstrInfo::loadRegFromStackSlot!");
   }
 
+  /// expandPostRAPseudo - This function is called for all pseudo instructions
+  /// that remain after register allocation. Many pseudo instructions are
+  /// created to help register allocation. This is the place to convert them
+  /// into real instructions. The target can edit MI in place, or it can insert
+  /// new instructions and erase MI. The function should return true if
+  /// anything was changed.
+  bool expandPostRAPseudo(MachineBasicBlock::iterator MI) const {
+    return false;
+  }
+
   /// emitFrameIndexDebugValue - Emit a target-dependent form of
   /// DBG_VALUE encoding the address of a frame index.  Addresses would
   /// normally be lowered the same way as other addresses on the target,
diff --git a/lib/CodeGen/ExpandPostRAPseudos.cpp b/lib/CodeGen/ExpandPostRAPseudos.cpp
index 78382f5..623b67d 100644
--- a/lib/CodeGen/ExpandPostRAPseudos.cpp
+++ b/lib/CodeGen/ExpandPostRAPseudos.cpp
@@ -202,17 +202,26 @@ bool ExpandPostRA::runOnMachineFunction(MachineFunction &MF) {
        mbbi != mbbe; ++mbbi) {
     for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
          mi != me;) {
-      MachineBasicBlock::iterator nmi = llvm::next(mi);
       MachineInstr *MI = mi;
-      assert(!MI->isInsertSubreg() && "INSERT_SUBREG should no longer appear");
-      assert(MI->getOpcode() != TargetOpcode::EXTRACT_SUBREG &&
-             "EXTRACT_SUBREG should no longer appear");
-      if (MI->isSubregToReg()) {
+      // Advance iterator here because MI may be erased.
+      ++mi;
+      switch (MI->getOpcode()) {
+      case TargetOpcode::SUBREG_TO_REG:
         MadeChange |= LowerSubregToReg(MI);
-      } else if (MI->isCopy()) {
+        break;
+      case TargetOpcode::COPY:
         MadeChange |= LowerCopy(MI);
+        break;
+      case TargetOpcode::DBG_VALUE:
+        continue;
+      case TargetOpcode::INSERT_SUBREG:
+      case TargetOpcode::EXTRACT_SUBREG:
+        llvm_unreachable("Sub-register pseudos should have been eliminated.");
+      default:
+        if (MI->getDesc().isPseudo())
+          MadeChange |= TII->expandPostRAPseudo(MI);
+        break;
       }
-      mi = nmi;
     }
   }
 
diff --git a/utils/TableGen/InstrInfoEmitter.cpp b/utils/TableGen/InstrInfoEmitter.cpp
index 1cf7c90..35fe728 100644
--- a/utils/TableGen/InstrInfoEmitter.cpp
+++ b/utils/TableGen/InstrInfoEmitter.cpp
@@ -268,6 +268,7 @@ void InstrInfoEmitter::emitRecord(const CodeGenInstruction &Inst, unsigned Num,
      << Inst.TheDef->getName() << "\", 0";
 
   // Emit all of the target indepedent flags...
+  if (Inst.isPseudo)           OS << "|(1<<MCID::Pseudo)";
   if (Inst.isReturn)           OS << "|(1<<MCID::Return)";
   if (Inst.isBranch)           OS << "|(1<<MCID::Branch)";
   if (Inst.isIndirectBranch)   OS << "|(1<<MCID::IndirectBranch)";