as: Xtensa Registers

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1 9.55.2.2 Register Names
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1 The assembly syntax for a register file entry is the "short" name for a
1 TIE register file followed by the index into that register file.  For
1 example, the general-purpose 'AR' register file has a short name of 'a',
1 so these registers are named 'a0'...'a15'.  As a special feature, 'sp'
1 is also supported as a synonym for 'a1'.  Additional registers may be
1 added by processor configuration options and by designer-defined TIE
1 extensions.  An initial '$' character is optional in all register names.
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