[GISel]: Add support for CSEing continuously during GISel passes.

https://reviews.llvm.org/D52803

This patch adds support to continuously CSE instructions during
each of the GISel passes. It consists of a GISelCSEInfo analysis pass
that can be used by the CSEMIRBuilder.

llvm-svn: 351283
diff --git a/llvm/lib/Target/Mips/MipsPreLegalizerCombiner.cpp b/llvm/lib/Target/Mips/MipsPreLegalizerCombiner.cpp
index c355a0e..1cff1c8 100644
--- a/llvm/lib/Target/Mips/MipsPreLegalizerCombiner.cpp
+++ b/llvm/lib/Target/Mips/MipsPreLegalizerCombiner.cpp
@@ -73,7 +73,7 @@
   auto *TPC = &getAnalysis<TargetPassConfig>();
   MipsPreLegalizerCombinerInfo PCInfo;
   Combiner C(PCInfo, TPC);
-  return C.combineMachineInstrs(MF);
+  return C.combineMachineInstrs(MF, nullptr);
 }
 
 char MipsPreLegalizerCombiner::ID = 0;