target/ppc: Fix FPSCR.FI bit being cleared when it shouldn't

According to Power ISA, the FI bit in FPSCR is non-sticky.
This means that if an instruction is said to modify the FI bit, then
it should be set or cleared depending on the result of the
instruction. Otherwise, it should be kept as was before.

However, the following inconsistency was found when comparing results
from the hardware (tested on both a Power 9 processor and in
Power 10 Mambo):

(FI bit is set before the execution of the instruction)
Hardware: xscmpeqdp(0xff..ff, 0xff..ff) = FI: SET -> SET
QEMU: xscmpeqdp(0xff..ff, 0xff..ff) = FI: SET -> CLEARED

As the FI bit is non-sticky, and xscmpeqdp does not list it as a field
that is changed by the instruction, it should not be changed after its
execution.
This is happening to multiple instructions in the vsx implementations.

If the ISA does not list the FI bit as altered for a particular
instruction, then it should be kept as it was before the instruction.

QEMU is not following this behavior. Affected instructions include:
- xv* (all vsx-vector instructions);
- xscmp*, xsmax*, xsmin*;
- xstdivdp and similars;
(to identify the affected instructions, just search in the ISA for
 the instructions that does not list FI in "Special Registers Altered")

Most instructions use the function do_float_check_status() to commit
changes in the inexact flag. So the fix is to add a parameter to it
that will control if the bit FI should be changed or not.
All users of do_float_check_status() are then modified to provide this
argument, controlling if that specific instruction changes bit FI or
not.
Some macro helpers are responsible for both instructions that change
and instructions that aren't suposed to change FI. This seems to always
overlap with the sfprf flag. So, reuse this flag for this purpose when
applicable.

Signed-off-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220517161522.36132-2-victor.colombo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

0 files changed, 0 insertions, 0 deletions