Jump threading

Not to be confused with Threaded code.

In computing, jump threading is a compiler optimization of one jump directly to a second jump. If the second condition is a subset or inverse of the first, it can be eliminated, or threaded through the first jump.^[1] This is easily done in a single pass through the program, following acyclic chained jumps until the compiler arrives at a fixed point.

Example

The following pseudocode demonstrates when a jump may be threaded.

   10. a = SomeNumber();
   20. IF a > 10 GOTO 50
   ...
   50. IF a > 0 GOTO 100
   ...

The jump on line 50 will always be taken if the jump on line 20 is taken. Therefore the jump on line 20 may safely be modified to jump directly to line 100.

References

↑ https://gcc.gnu.org/onlinedocs/gcc-3.4.5/gcc/Optimize-Options.html

Compiler optimizations

Basic block	Peephole optimization

Loop optimization	Induction variable Strength reduction Loop fusion Loop inversion Loop interchange Loop-invariant code motion Loop nest optimization Loop unrolling Loop splitting Loop unswitching Software pipelining Automatic parallelization

Data-flow analysis	Common subexpression elimination Constant folding Induction variable recognition and elimination Dead store elimination Use-define chain Live variable analysis Available expression

SSA-based	Global value numbering Sparse conditional constant propagation

Code generation	Register allocation Instruction selection Instruction scheduling Rematerialization

Functional	Tail call elimination Deforestation

Global	Interprocedural optimization

Other	Bounds-checking elimination Dead code elimination Inline expansion Jump threading

Static analysis	Alias analysis Pointer analysis Shape analysis Escape analysis Array access analysis Dependence analysis Control flow analysis Data flow analysis

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