as: Xtensa Opcodes

1 
1 9.55.2.1 Opcode Names
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1 See the 'Xtensa Instruction Set Architecture (ISA) Reference Manual' for
1 a complete list of opcodes and descriptions of their semantics.
1 
1    If an opcode name is prefixed with an underscore character ('_'),
1 'as' will not transform that instruction in any way.  The underscore
DONTPRINTYET 11 prefix disables both optimization (⇒Xtensa Optimizations Xtensa
 Optimizations.) and relaxation (*noteXtensa Relaxation: Xtensa
1DONTPRINTYET 11 prefix disables both optimization (⇒Xtensa Optimizations Xtensa
 Optimizations.) and relaxation (⇒Xtensa Relaxation Xtensa

 Relaxation.) for that particular instruction.  Only use the underscore
1 prefix when it is essential to select the exact opcode produced by the
1 assembler.  Using this feature unnecessarily makes the code less
1 efficient by disabling assembler optimization and less flexible by
1 disabling relaxation.
1 
1    Note that this special handling of underscore prefixes only applies
1 to Xtensa opcodes, not to either built-in macros or user-defined macros.
1 When an underscore prefix is used with a macro (e.g., '_MOV'), it refers
1 to a different macro.  The assembler generally provides built-in macros
1 both with and without the underscore prefix, where the underscore
1 versions behave as if the underscore carries through to the instructions
1 in the macros.  For example, '_MOV' may expand to '_MOV.N'.
1 
1    The underscore prefix only applies to individual instructions, not to
1 series of instructions.  For example, if a series of instructions have
1 underscore prefixes, the assembler will not transform the individual
1 instructions, but it may insert other instructions between them (e.g.,
1 to align a 'LOOP' instruction).  To prevent the assembler from modifying
1 a series of instructions as a whole, use the 'no-transform' directive.
1 ⇒transform Transform Directive.
1