[MIPS GlobalISel] Select branch instructions

Select G_BR and G_BRCOND for MIPS32.
Unconditional branch G_BR does not have register operand,
for that reason we only add tests.
Since conditional branch G_BRCOND compares register to zero on MIPS32,
explicit extension must be performed on i1 condition in order to set
high bits to appropriate value.

Differential Revision: https://reviews.llvm.org/D58182

llvm-svn: 354022
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index b3170b0..298a916 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -1176,7 +1176,7 @@
   }
   case TargetOpcode::G_BRCOND:
     Observer.changingInstr(MI);
-    widenScalarSrc(MI, WideTy, 0, TargetOpcode::G_ANYEXT);
+    widenScalarSrc(MI, WideTy, 0, MIRBuilder.getBoolExtOp(false, false));
     Observer.changedInstr(MI);
     return Legalized;