[Qemu-devel] [PATCH 0/5] target-arm: Implement UDIV/SDIV and fused multiply-accumulate

[Peter Maydell]

This patch series implements support in QEMU for some (user-mode)
instructions which are present on some recent processors
(eg Cortex-A15).

The new instructions are UDIV/SDIV (previously only available as a Thumb
encoding for M-class cores, now an optional extension to ARMv7A), and
the fused-multiply-accumulate instructions VFMA, VFMS, VFNMA, VFNMS.
We don't (yet) support a specific processor for system mode with these
extensions, so they are enabled only for ARM_CPUID_ANY.

The most interesting part of this is the fused multiply-accumulate
support which I have added to softfloat. Although this is only used
by ARM at the moment I've put in some flags which should be sufficient
for the variants provided by other architectures. (Specifically,
x86, Itanium and SPARC64 VI all need the "negate product" flag
since they have "-(a*b)+c" instructions. PPC needs the "negate
result" and "negate addend" flags.)

The NaN handling hooks are not as clean as the 2-operand versions.
This is because there isn't really any consensus about what order
the operands in a fused-mac should be in; ARM uses c+(a*b), PPC
does something else, and so on. So even if there was more than
one 3-operand IEEE operation a generic "pick one of 3 NaNs"
function would be tricky; I opted to just be clear about the
fact this was fused-mac specific. I've provided the PPC implementation
of the NaN-selection function because the architecture manual was
helpfully clear about what it was. x86 and SPARC don't seem to
document the behaviour in this area :-(

I've thrown in the "reinstate target-specific NaN handling" patch
I posted earlier this week just to avoid possible patch conflicts.

As usual, this has all been tested with a long run on my random
instruction generation testbed.


Peter Maydell (5):
  softfloat: Reinstate accidentally disabled target-specific NaN
    handling
  target-arm: v6 media multiply space: UNDEF on unassigned encodings
  target-arm: Add ARM UDIV/SDIV support
  softfloat: Implement fused multiply-add
  target-arm: Implement VFPv4 fused multiply-accumulate insns

 fpu/softfloat-specialize.h |  178 ++++++++++++++++++
 fpu/softfloat.c            |  433 ++++++++++++++++++++++++++++++++++++++++++++
 fpu/softfloat.h            |   14 ++
 target-arm/cpu.h           |    1 +
 target-arm/helper.c        |   14 ++
 target-arm/helper.h        |    3 +
 target-arm/translate.c     |  115 +++++++++++-
 7 files changed, 754 insertions(+), 4 deletions(-)