two and three pass compiler architecture, Slides of Compiler Construction

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Compiler

Construction

Lecture 4

The Back End

Register Allocation:  Have each value in a register when it is used. Instruction selection IR (^) machine code errors Register allocation Instruction scheduling

IR IR

The Back End

Register Allocation:  (^) Can change instruction choices and insert LOADs and STOREs. Instruction selection IR (^) machine code errors Register allocation Instruction scheduling

IR IR

The Back End

Register Allocation:  Optimal register allocation is NP-Complete. Instruction selection IR (^) machine code errors Register allocation Instruction scheduling

IR IR

The Back End

Instruction Scheduling:  Use all functional units productively. Instruction selection IR (^) machine code errors Register allocation Instruction scheduling

IR IR

The Back End

Instruction Scheduling:  (^) Optimal scheduling is NP-Complete in nearly all cases. Instruction selection IR (^) machine code errors Register allocation Instruction scheduling

IR IR

Three-pass Compiler

 Analyzes IR and rewrites (or transforms ) IR Front End Source code machine code errors Middle End Back End

IR IR

Three-pass Compiler

 Primary goal is to reduce running time of the compiled code Front End Source code machine code errors Middle End Back End

IR IR

Three-pass Compiler

 (^) Must preserve “meaning” of the code.  (^) Measured by values of named variables Front End Source code machine code errors Middle End Back End

IR IR

Optimizer

 Modern optimizers are structured as a series of passes Opt 1

IR IR

errors Opt 2 Opt n

IR

IR Opt 3

IR

Optimizer

Typical transformations

Move a computation to a less frequently executed place Opt 1

IR IR

errors Opt 2 Opt n

IR

IR Opt 3

IR

Optimizer

Typical transformations

Specialize some computation based on context Opt 1

IR IR

errors Opt 2 Opt n

IR

IR Opt 3

IR

Optimizer

Typical transformations  Remove useless or unreachable code Opt 1

IR IR

errors Opt 2 Opt n

IR

IR Opt 3

IR

Optimizer

Typical transformations  Encode an idiom in some particularly efficient form Opt 1

IR IR

errors Opt 2 Opt n

IR

IR Opt 3

IR