[mips] SelectionDAGISel subclasses now follow the optimization level.

Summary:
It was recently discovered that, for Mips's SelectionDAGISel subclasses,
all optimization levels caused SelectionDAGISel to behave like -O2.

This change adds the necessary plumbing to initialize the optimization level.

Reviewers: andrew.w.kaylor

Subscribers: andrew.w.kaylor, sdardis, dean, llvm-commits, vradosavljevic, petarj, qcolombet, probinson, dsanders

Differential Revision: https://reviews.llvm.org/D14900

llvm-svn: 275410
diff --git a/llvm/lib/Target/Mips/MipsTargetMachine.cpp b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
index 8366129..c248c3a 100644
--- a/llvm/lib/Target/Mips/MipsTargetMachine.cpp
+++ b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
@@ -229,8 +229,8 @@
 // the ISelDag to gen Mips code.
 bool MipsPassConfig::addInstSelector() {
   addPass(createMipsModuleISelDagPass(getMipsTargetMachine()));
-  addPass(createMips16ISelDag(getMipsTargetMachine()));
-  addPass(createMipsSEISelDag(getMipsTargetMachine()));
+  addPass(createMips16ISelDag(getMipsTargetMachine(), getOptLevel()));
+  addPass(createMipsSEISelDag(getMipsTargetMachine(), getOptLevel()));
   return false;
 }