This patchset fixes a regression that I introduced in my recent
refactoring of softfloat NaN handling, in commit 8adcff4ae7
("fpu: handle raising Invalid for infzero in pick_nan_muladd").
When I wrote that code I was under the impression that all
architectures would raise Invalid for the "inf * zero + NaN"
case of a fused multiply-add. However, IEEE 754-2008 makes this
impdef for QNaN: an architecture can choose whether to raise
Invalid or not.For i386, SDM section 14.5.2 documents that for the 0 * Inf + NaN case that it will only raise the Invalid exception when the input is a signalling NaN, and so the behaviour change in 8adcff4ae7 that caused it to raise Invalid also for the QNaN case is wrong. The first commit here adds a knob to the softfloat code to allow an architecture to disable the "raise Invalid" that is the default, and makes x86 set that. The second commit is a test case for x86 check-tcg that exercises this corner case. We do not revert here the behaviour change for hppa, sh4 or tricore: * The sh4 manual is clear that it should signal Invalid * The tricore manual is a bit vague but doesn't say it shouldn't * The hppa manual doesn't talk about fused multiply-add corner cases at all The test case also includes a disabled test for a different x86 fma corner case; this is one that's not a regression. I've left it in the test case code because it's the justification for why the test harness has the support for testing fma insns with FTZ set. I'm working on a fix for that but I don't think it should be tangled up with fixing this regression. thanks -- PMM Peter Maydell (2): target/i386: Do not raise Invalid for 0 * Inf + QNaN tests/tcg/x86_64/fma: Test some x86 fused-multiply-add cases include/fpu/softfloat-types.h | 16 ++++- target/i386/tcg/fpu_helper.c | 5 +- tests/tcg/x86_64/fma.c | 109 +++++++++++++++++++++++++++++++ fpu/softfloat-parts.c.inc | 5 +- tests/tcg/x86_64/Makefile.target | 1 + 5 files changed, 130 insertions(+), 6 deletions(-) create mode 100644 tests/tcg/x86_64/fma.c -- 2.34.1
