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

2 files changed, 18 insertions, 0 deletions

diff --git a/include/llvm/MC/MCInstrDesc.h b/include/llvm/MC/MCInstrDesc.h
index 7061fcb012..aafa800c1a 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 e6e963c03e..bbe5897821 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,