X86 Peephole: fold loads to the source register operand if possible.

Machine CSE and other optimizations can remove instructions so folding
is possible at peephole while not possible at ISel.

rdar://10554090 and rdar://11873276


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160919 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 0 deletions

diff --git a/include/llvm/Target/TargetInstrInfo.h b/include/llvm/Target/TargetInstrInfo.h
index 73efc50..ba5e05d 100644
--- a/include/llvm/Target/TargetInstrInfo.h
+++ b/include/llvm/Target/TargetInstrInfo.h
@@ -14,6 +14,7 @@
 #ifndef LLVM_TARGET_TARGETINSTRINFO_H
 #define LLVM_TARGET_TARGETINSTRINFO_H
 
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/CodeGen/DFAPacketizer.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -693,6 +694,16 @@ public:
     return false;
   }
 
+  /// optimizeLoadInstr - Try to remove the load by folding it to a register
+  /// operand at the use. We fold the load instructions if and only if the
+  /// def and use are in the same BB.
+  virtual MachineInstr* optimizeLoadInstr(MachineInstr *MI,
+                        const MachineRegisterInfo *MRI,
+                        SmallSet<unsigned, 4> &FoldAsLoadDefRegs,
+                        MachineInstr *&DefMI) const {
+    return 0;
+  }
+
   /// FoldImmediate - 'Reg' is known to be defined by a move immediate
   /// instruction, try to fold the immediate into the use instruction.
   virtual bool FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,