Scalar replacement in the presence of conditional control flow

Document Type


Publication Date



Most conventional compilers fail to allocate array elements to registers because standard data‐flow analysis treats arrays like scalars, making it impossible to analyze the definitions and uses of individual array elements. This deficiency is particularly troublesome for floating‐point registers, which are most often used as temporary repositories for subscripted variables. This paper presents a source‐to‐source transformation, called scalar replacement, that finds opportunities for reuse of subscripted variables and replaces the references involved by references to temporary scalar variables. The scalar replaced variables are more likely to be assigned to registers by the coloring‐based register allocators found in most compilers than are their unreplaced counterparts. The algorithm presented here extends previous techniques for scalar replacement by allowing the presence of forward conditional control flow within loop bodies through the mapping of partial redundancy elimination to scalar replacement. Finally, experimental results show that scalar replacement is extremely effective. On kernels, integer‐factor improvements over code generated by a good optimizing compiler of conventional design are possible. Copyright © 1994 John Wiley & Sons, Ltd

Publication Title

Software: Practice and Experience