[0/4] target/i386: Emulate ftz and denormal flag bits correctly

Message

Peter Maydell Feb. 13, 2025, 2:26 p.m. UTC

This is a set of four patches to target/i386 which use the core
fpu functionality we just landed for Arm FEAT_AFP to correct
the emulation of some corner cases of x86 floating point:
 * when we are flushing denormal outputs to zero, this should
   be done after rounding, not before
 * the MXCSR.DE and FPUS.DE bits indicate when a denormal input
   was not flushed and was used in an fp operation; we previously
   weren't implementing these semantics

All four patches have been reviewed by RTH. Testing is a bit
light (make check-tcg and make check-functional), because AFAIK
there is no freely available comprehensive FP testsuite for x86,
and risu doesn't support x86 currently so I can't do the same kind
of random-instruction-testing I could for Arm.

thanks
-- PMM

Peter Maydell (4):
  target/i386: Detect flush-to-zero after rounding
  target/i386: Use correct type for get_float_exception_flags() values
  target/i386: Wire up MXCSR.DE and FPUS.DE correctly
  tests/tcg/x86_64/fma: add test for exact-denormal output

 target/i386/ops_sse.h        |  16 +++---
 target/i386/tcg/fpu_helper.c | 101 +++++++++++++++++------------------
 tests/tcg/x86_64/fma.c       |  17 ++++--
 3 files changed, 68 insertions(+), 66 deletions(-)