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28f13bccbe
Currently we handle flushing of output denormals in uncanon_normal always before we deal with rounding. This works for architectures that detect tininess before rounding, but is usually not the right place when the architecture detects tininess after rounding. For example, for x86 the SDM states that the MXCSR FTZ control bit causes outputs to be flushed to zero "when it detects a floating-point underflow condition". This means that we mustn't flush to zero if the input is such that after rounding it is no longer tiny. At least one of our guest architectures does underflow detection after rounding but flushing of denormals before rounding (MIPS MSA); this means we need to have a config knob for this that is separate from our existing tininess_before_rounding setting. Add an ftz_detection flag. For consistency with tininess_before_rounding, we make it default to "detect ftz after rounding"; this means that we need to explicitly set the flag to "detect ftz before rounding" on every existing architecture that sets flush_to_zero, so that this commit has no behaviour change. (This means more code change here but for the long term a less confusing API.) For several architectures the current behaviour is either definitely or possibly wrong; annotate those with TODO comments. These architectures are definitely wrong (and should detect ftz after rounding): * x86 * Alpha For these architectures the spec is unclear: * MIPS (for non-MSA) * RX * SH4 PA-RISC makes ftz detection IMPDEF, but we aren't setting the "tininess before rounding" setting that we ought to. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> |
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| Kconfig | 4 years ago | |
| cpu-param.h | 2 weeks ago | |
| cpu-qom.h | 1 year ago | |
| cpu.c | 3 weeks ago | |
| cpu.h | 3 weeks ago | |
| fpu_helper.c | 2 weeks ago | |
| gdbstub.c | 9 months ago | |
| helper.c | 3 weeks ago | |
| helper.h | 3 weeks ago | |
| insns.decode | 3 weeks ago | |
| int_helper.c | 3 weeks ago | |
| machine.c | 3 weeks ago | |
| mem_helper.c | 3 weeks ago | |
| meson.build | 1 year ago | |
| op_helper.c | 2 months ago | |
| sys_helper.c | 3 weeks ago | |
| trace-events | 1 year ago | |
| trace.h | 5 years ago | |
| translate.c | 3 weeks ago | |