Add a quick pass to optimize sign / zero extension instructions. For targets where the pre-extension values are available in the subreg of the result of the extension, replace the uses of the pre-extension value with the result + extract_subreg.

For now, this pass is fairly conservative. It only perform the replacement when both the pre- and post- extension values are used in the block. It will miss cases where the post-extension values are live, but not used.

llvm-svn: 93278

1 files changed, 9 insertions, 7 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index 6ae7808e2dd..0ab85f4f45b 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -448,13 +448,15 @@ public:
                            unsigned &SrcReg, unsigned &DstReg,
                            unsigned &SrcSubIdx, unsigned &DstSubIdx) const;
 
-  /// isCoalescableInstr - Return true if the instruction is "coalescable". That
-  /// is, it's like a copy where it's legal for the source to overlap the
-  /// destination. e.g. X86::MOVSX64rr32.
-  virtual bool isCoalescableInstr(const MachineInstr &MI, bool &isCopy,
-                                unsigned &SrcReg, unsigned &DstReg,
-                                unsigned &SrcSubIdx, unsigned &DstSubIdx) const;
-
+  /// isCoalescableExtInstr - Return true if the instruction is a "coalescable"
+  /// extension instruction. That is, it's like a copy where it's legal for the
+  /// source to overlap the destination. e.g. X86::MOVSX64rr32. If this returns
+  /// true, then it's expected the pre-extension value is available as a subreg
+  /// of the result register. This also returns the sub-register index in
+  /// SubIdx.
+  virtual bool isCoalescableExtInstr(const MachineInstr &MI,
+                                     unsigned &SrcReg, unsigned &DstReg,
+                                     unsigned &SubIdx) const;
 
   unsigned isLoadFromStackSlot(const MachineInstr *MI, int &FrameIndex) const;
   /// isLoadFromStackSlotPostFE - Check for post-frame ptr elimination