Editing Optimizing compiler (section)

=== SSA-based optimizations ===
These optimizations are intended to be done after transforming the program into a special form called [[SSA (compilers)|Static Single Assignment]], in which every variable is assigned in only one place. Although some function without SSA, they are most effective with SSA. Many optimizations listed in other sections also benefit with no special changes, such as register allocation.

;[[Global value numbering]]: GVN eliminates redundancy by constructing a value graph of the program, and then determining which values are computed by equivalent expressions. GVN can identify some redundancy that [[common subexpression elimination]] cannot, and vice versa.

;[[Sparse conditional constant propagation]]: Combines constant propagation, [[constant folding]], and [[dead-code elimination]], and improves upon what is possible by running them separately.<ref>{{cite journal|last1=Wegman|first1=Mark N.|last2=Zadeck|first2=F. Kenneth|url=https://bears.ece.ucsb.edu/class/ece253/papers/wegman91.pdf|title=Constant Propagation with Conditional Branches|journal=[[ACM Transactions on Programming Languages and Systems]]|volume=13|issue=2|date=April 1991|pages=181–210|doi=10.1145/103135.103136}}</ref><ref>{{cite journal|last1=Click|first1=Clifford|last2=Cooper|first2=Keith.|url=https://scholarship.rice.edu/bitstream/handle/1911/96451/TR95-252.pdf?sequence=1&isAllowed=y|title=Combining Analyses, Combining Optimizations|journal=ACM Transactions on Programming Languages and Systems|volume=17|issue=2|date=March 1995|pages=181–196|doi=10.1145/201059.201061}}</ref> This optimization symbolically executes the program, simultaneously propagating constant values and eliminating portions of the [[control-flow graph]] that this makes unreachable.