[BUG] Incorrect Accumulation of ‘OF’ Flag in fflags After Executing fsqrt.d on Infinity

[youzi27]

Bug Description

When executing the fsqrt.d instruction on a double-precision floating-point value representing positive infinity (0x7ff0000000000000), the Overflow (OF) flag in the fflags register is erroneously set. According to the IEEE 754 standard and the RISC-V specification, the fsqrt.d operation should not lead to an overflow situation when the input is infinity. This also results in inconsistency with Spike's output

Expected Behavior:
The OF flag in the fflags register should remain clear (i.e., not set) after performing a square root operation on an infinite value, as the result is well-defined and should be positive infinity.

Actual Behavior:
The OF flag is set in the fflags register, indicating an overflow, which contradicts the expected behavior defined by the IEEE 754 standard and RISC-V floating-point operation guidelines.

Steps to Reproduce:

1. Load a double-precision floating-point register with the value 0x7ff0000000000000 (positive infinity).
2. Execute the fsqrt.d instruction on this register.
3. Check the fflags register; observe that the OF flag is incorrectly set.

EDIT: A PR has been submitted pulp-platform/fpu_div_sqrt_mvp#25

EDIT: And See: openhwgroup/cva6#2058