[X86][GlobalISel] Initial implementation , select G_ADD gpr, gpr

Summary: Initial implementation for X86InstructionSelector. Handle selection COPY and G_ADD/G_SUB gpr, gpr .

Reviewers: qcolombet, rovka, zvi, ab

Reviewed By: rovka

Subscribers: mgorny, dberris, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D29816

llvm-svn: 295824

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp b/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
index 5c34da0dc55..1e1d0392483 100644
--- a/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
@@ -55,6 +55,13 @@ bool InstructionSelector::constrainSelectedInstRegOperands(
     // constrainOperandRegClass does that for us.
     MO.setReg(constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(),
                                        Reg, OpI));
+
+    // Tie uses to defs as indicated in MCInstrDesc.
+    if (MO.isUse()) {
+      int DefIdx = I.getDesc().getOperandConstraint(OpI, MCOI::TIED_TO);
+      if (DefIdx != -1)
+        I.tieOperands(DefIdx, OpI);
+    }
   }
   return true;
 }