Overview of backend passes.

Overview of backend passes.

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The back-end performs a series of passes that can possibly introduce some backtracking - returning to a given point in the sequence of passes to re-run it again, possibly with new information. This usually happens when PHV or table allocation fails.

The back-end starts with IR that was already transformed from front-end/mid-end IR into back-end IR (via BackendConverter). Also the back-end works on individual pipes in the program, not the entire program at once. This means that the input of the back-end is a back-end IR of a pipe and the output is a assembly file for this pipe.

There are currently two top-level flows. Changing between them can be done by setting options.alt_phv_alloc. These two flows are:

• Main flow:
  1. Run full PHV allocation
  2. Run MAU allocation
• Alternative flow:
  1. Run trivial PHV allocation
  2. Run MAU allocation
  3. Run full PHV allocation
• Note: Both flows include different optimization/transformation passes in between and also possible backtracking.

There are two special types of passes:

• Dumping passes - these passes dump some information from the compiler usually some part of IR.
  • DumpPipe
  • DumpParser
  • DumpTableFlowGraph
  • DumpJsonGraph
• Logging passes - these passes create log/report files.
  • LogFlexiblePacking
  • CollectPhvLoggingInfo
  • GeneratePrimitiveInfo
  • LiveRangeReport
  • BFN::CollectIXBarInfo