 RealView Compiler User's Guide | |
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RealView Compiler User's Guide
Preface Introduction Getting started with the ARM Compiler Compiler Features Coding Practices Optimizing code
Optimizing for size versus speed Optimization levels and the debug view Selecting the target device Optimizing loops Using volatile Code metrics Measuring code and data sizes Measuring stack use Reducing debug information in objects and librarie Functions Minimizing parameter passing overhead __value_in_regs __pure Placing ARM function qualifiers Inlining How the compiler decides to inline When is it practical for the compiler to inline? Managing inlining Inlining functions across multiple files Debugging data and the --[no]_inline keyword Marking functions as static Setting breakpoints on inlined functions in ROM im Aligning data About data alignment The __packed qualifier and unaligned accesses to d __packed structures versus individually __packed f Using floating-point arithmetic Support for floating-point operations VFP architectures The --fpu option Floating-point linkage The --fpmode option Using the --fpu option VFP support Trapping and identifying division-by-zero errors Integer division (Software) Floating point division Support for ARM architecture v6 Instruction generation Alignment support Endian support Diagnostic Messages Using the Inline and Embedded Assemblers SemihostingMinimizing parameter passing overhead
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| Home > Coding Practices > Functions > Minimizing parameter passing overhead | |||
There are several ways in which you can minimize the overhead of passing parameters to functions. For example:
Ensure that functions take four or fewer arguments, each a word or less in size. Registers
R0-R3can then be used in place of the stack for passing the parameters.Note
In C++, non-static member functions have an implicit
thispointer argument, which is usually passed inR0. Therefore only three more registers are available for passing additional arguments in this case.Ensure that a function does a significant amount of work if it requires more than four arguments, so that the cost of passing the stacked arguments is outweighed.
Put related arguments in a structure, and pass a pointer to the structure in any function call. This reduces the number of parameters and increases readability.
Minimize the number of long long parameters, as these take two argument words.
Minimize the number of double parameters if software floating-point is enabled.
Avoid functions with a variable number of parameters. Functions taking a variable number of arguments effectively pass all their arguments on the stack.
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