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Compiler User Guide

Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler Coding Practices Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler support for inline assembly language Inline assembler support in the compiler Restrictions on inline assembler support in the co Inline assembly language syntax with the __asm key Inline assembly language syntax with the asm keywo Inline assembler rules for compiler keywords __asm Restrictions on inline assembly operations in C an Inline assembler register restrictions in C and C+ Inline assembler processor mode restrictions in C Inline assembler Thumb instruction set restriction Inline assembler Vector Floating-Point (VFP) restr Inline assembler instruction restrictions in C and Miscellaneous inline assembler restrictions in C a Inline assembler and register access in C and C++ Inline assembler and the # constant expression spe Inline assembler and instruction expansion in C an Expansion of inline assembler instructions that us Expansion of inline assembler load and store instr Inline assembler effect on processor condition fla Inline assembler expression operands in C and C++ Inline assembler register list operands in C and C Inline assembler intermediate operands in C and C+ Inline assembler function calls and branches in C Inline assembler branches and labels in C and C++ Inline assembler and virtual registers Embedded assembler support in the compiler Embedded assembler syntax in C and C++ Effect of compiler ARM and Thumb states on embedde Restrictions on embedded assembly language functio Compiler generation of embedded assembly language Access to C and C++ compile-time constant expressi Differences between expressions in embedded assemb Manual overload resolution in embedded assembler __offsetof_base keyword for related base classes i Compiler-supported keywords for calling class memb __mcall_is_virtual(D, f) __mcall_is_in_vbase(D, f) __mcall_offsetof_vbase(D, f) __mcall_this_offset(D, f) __vcall_offsetof_vfunc(D, f) Calling nonstatic member functions in embedded ass Calling a nonvirtual member function Calling a virtual member function Accessing sp (r13), lr (r14), and pc (r15) Differences in compiler support for inline and emb Compiler Command-line Options Language Extensions Compiler-specific Features C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Differences in compiler support for inline and embedded assembly code

6.45 Differences in compiler support for inline and embedded assembly code

There are differences between the ways inline and embedded assembly are compiled.

Specifically:
  • Inline assembly code uses a high level of processor abstraction, and is integrated with the C and C++ code during code generation. Therefore, the compiler optimizes the C and C++ code and the assembly code together.
  • Unlike inline assembly code, embedded assembly code is assembled separately from the C and C++ code to produce a compiled object that is then combined with the object from the compilation of the C or C++ source.
  • Inline assembly code can be inlined by the compiler, but embedded assembly code cannot be inlined, either implicitly or explicitly.
The following table summarizes the main differences between inline assembler and embedded assembler.

Table 6-1 Differences between inline and embedded assembler

Feature Embedded assembler Inline assembler
Instruction set ARM and Thumb.
ARM on all processors.
Thumb on processors with Thumb-2 technology.
ARM assembler directives All supported. None supported.
ARMv6 instructions All supported.
Supports most instructions, with some exceptions, for example SETEND and some of the system extensions. The complete set of ARMv6 SIMD instructions is supported.
ARMv7 instructions All supported. Supports most instructions.
VFP instructions All supported. VFPv2 only.
C/C++ expressions Constant expressions only. Full C/C++ expressions.
Optimization of assembly code No optimization. Full optimization.
Inlining Never. Possible.
Register access Specified physical registers are used. You can also use PC, LR and SP.
Uses virtual registers. Using sp (r13), lr (r14), and pc (r15) gives an error.
Return instructions You must add them in your code. Generated automatically. (The BX, BXJ, and BLX instructions are not supported.)
BKPT instruction Supported directly. Not supported.
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