target-mips: Add abs2008 flavor of <ABS|NEG>.<S|D>
Updated handling of instructions <ABS|NEG>.<S|D>. Note that legacy (pre-abs2008) ABS and NEG instructions are arithmetic (and, therefore, any NaN operand causes signaling invalid operation), while abs2008 ones are non-arithmetic, always and only changing the sign bit, even for NaN-like operands. Details on these instructions are documented in [1] p. 35 and 359. Implementation-wise, abs2008 versions are implemented without helpers, for simplicity and performance sake. [1] "MIPS Architecture For Programmers Volume II-A: The MIPS64 Instruction Set Reference Manual", Imagination Technologies LTD, Revision 6.04, November 13, 2015 Signed-off-by: NThomas Schwinge <thomas@codesourcery.com> Signed-off-by: NMaciej W. Rozycki <macro@codesourcery.com> Signed-off-by: NAleksandar Markovic <aleksandar.markovic@imgtec.com> Reviewed-by: NLeon Alrae <leon.alrae@imgtec.com> Signed-off-by: NLeon Alrae <leon.alrae@imgtec.com>
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