Fix to removeRedundantMergeVariables.
Fix to removeRedundantMergeVariables.

HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark,CulpaBS/wbBach,diku-dk/futhark,ihc/futhark,diku-dk/futhark,mrakgr/futhark,HIPERFIT/futhark,HIPERFIT/futhark,diku-dk/futhark,ihc/futhark,mrakgr/futhark,mrakgr/futhark