a94b783952
The appended paves the way for leveraging the host FPU for a subset of guest FP operations. For most guest workloads (e.g. FP flags aren't ever cleared, inexact occurs often and rounding is set to the default [to nearest]) this will yield sizable performance speedups. The approach followed here avoids checking the FP exception flags register. See the added comment for details. This assumes that QEMU is running on an IEEE754-compliant FPU and that the rounding is set to the default (to nearest). The implementation-dependent specifics of the FPU should not matter; things like tininess detection and snan representation are still dealt with in soft-fp. However, this approach will break on most hosts if we compile QEMU with flags that break IEEE compatibility. There is no way to detect all of these flags at compilation time, but at least we check for -ffast-math (which defines __FAST_MATH__) and disable hardfloat (plus emit a #warning) when it is set. This patch just adds common code. Some operations will be migrated to hardfloat in subsequent patches to ease bisection. Note: some architectures (at least PPC, there might be others) clear the status flags passed to softfloat before most FP operations. This precludes the use of hardfloat, so to avoid introducing a performance regression for those targets, we add a flag to disable hardfloat. In the long run though it would be good to fix the targets so that at least the inexact flag passed to softfloat is indeed sticky. Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Emilio G. Cota <cota@braap.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> |
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| .. | ||
| softfloat-specialize.h | ||
| softfloat.c | ||