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The patterns of an individual RTL instruction describe which registersare inputs to that instruction and which registers are outputs fromthat instruction. However, it is often useful to know where thedefinition of a register input comes from and where the result ofa register output is used. One way of obtaining this informationis to use the RTL SSA form, which provides a Static Single Assignmentrepresentation of the RTL instructions.
The RTL SSA code is located in thertl-ssa subdirectory of the GCCsource tree. This section only gives a brief overview of it; pleasesee the comments in the source code for more details.