re PR tree-optimization/22278 (gcc -O2 discards cast to volatile)

        PR tree-opt/22278
        * gimplify.c (gimplify_expr): Use main variant type for the temp
        destination for a discarded volatile read.
        * tree-ssa.c (tree_ssa_useless_type_conversion_1): Don't elide
        casts between non-void types that change volatility.

From-SVN: r102169