[GlobalISel] Use the target preferred type for G_EXTRACT_VECTOR_ELT index.

Allows for better imported pattern re-use.

llvm-svn: 345265
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index ff2e61c..c9ed97a 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -878,6 +878,12 @@
     MIRBuilder.recordInsertion(&MI);
     return Legalized;
   }
+  case TargetOpcode::G_EXTRACT_VECTOR_ELT:
+    if (TypeIdx != 2)
+      return UnableToLegalize;
+    widenScalarSrc(MI, WideTy, 2, TargetOpcode::G_SEXT);
+    MIRBuilder.recordInsertion(&MI);
+    return Legalized;
   }
 }