Texas Instruments TMS320C2x, User Manual

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Using the C Compiler Optimizer
3-2
3.1 Using the C Compiler Optimizer
The optimizer runs as a separate pass between the parser and the code
generator. Figure 3
− 1 illustrates the execution flow of the compiler with stand-
alone optimization.
Figure 3 − 1. Compiling a C Program With the Optimizer
C source
file (.c)
Code
generator
Parser
Optimizer
.if file
.asm file
.opt file
The easiest way to invoke the optimizer is to use the dspcl shell program, spec-
ifying the
− o n option on the dspcl command line. The n denotes the level of
optimization (0, 1, 2, and 3), which controls the type and degree of optimiza-
tion:
-
− o0
J
Performs control-flow-graph simplification
J
Allocates variables to registers
J
Performs loop rotation
J
Eliminates unused code
J
Simplifies expressions and statements
J
Expands calls to functions declared inline
-
− o1
Performs all − o0 optimizations, plus:
J
Performs local copy/constant propagation
J
Removes unused assignments
J
Eliminates local common expressions
-
− o2
Performs all − o1 optimizations, plus:
J
Performs loop optimizations
J
Eliminates global common subexpressions
J
Eliminates global unused assignments
J
Converts array references in loops to incremented pointer form
J
Performs loop unrolling
The optimizer uses − o2 as the default if you use − o without an optimization
level.