IEEE_754 Compliance
The MIPS4 instruction set contains IEEE754 noncompliant instructions:
 recip.s/d (reciprocal 1/x) instruction is accurate to 1 ulp
 rsqrt.s/d (reciprocalsqrt: 1/sqrt(x)) instruction to 2 ulp

OPT:IEEE_arithmetic=X specify degree of noncompliance
and what to do with inf and NaN operands
X = 1 strict IEEE754 compliance; does not use the recip and rsqrt instructions (O1,2)
X = 2 optimize 0*x=0 and x/x=1 while x can be NaN (default at O3)
X = 3 any mathematically valid transformation is allowed, including recip & rsqrt instr.
21 cycles/iteration; 4% peak
1 cycles/iteration; 100% peak