-ffloat-store does address some issues on x87, but not all. By itself, -ffloat-store does double rounding (80-bit then 64-bit) which can produce different results than rounding directly to 64-bit in a single step.
When it can, SpiderMonkey also sets the x87's precision control field to 64-bit (see js::FIX_FPU), which avoids most of the double-rounding differences. However, the x87's precision control field only changes the effective size of the fractional part, and not the exponent part, so it still rounds differently than single-step rounding in extreme cases, for example 0x1.db3bd2a286944p-599 * 0x1.ce910af1d55cap-425. Also, the x87's load instructions automatically convert sNaN to qNaN, which is a different bit pattern, which can be observed in various places in wasm. Dan On Tue, Jan 3, 2017 at 11:45 PM, <mskal...@redhat.com> wrote: > I quess I was dealing with this problem. > > "-ffloat-store" gcc option was working for me to fix floating point > correctness issues. To make jstests passing on x86... > > > On Tuesday, January 3, 2017 at 11:48:49 AM UTC+1, Benjamin Bouvier wrote: > > Following > > https://groups.google.com/d/topic/mozilla.dev.platform/ > v3Mz5iuMkig/discussion, > > Firefox builds now include SSE2 flags on all tier-1 32-bits x86 > platforms. > > The Spidermonkey JS shell using a different build system, the SSE2 flags > > have not been included until bug 1326027 landed. Bug 1326027 also > included > > changes that require SSE2 to be enabled on these platforms (= x86 and > ARM32 > > simulator, since it uses x86 as an host). > > > > If you see wasm related failures when building on x86 32-bits, add these > > flags to your compiler flags: > > - "-msse -msse2 -mfpmath=sse" on linux32 builds, with gcc or clang > > - "-arch:SSE2" on win32 builds, with cl > > > > If you simply use the autospider.py tool [1], these flags will now be > > included by default. This is what's used on our CI infrastructure. > > > > Building without SSE2 support on x86 is still possible, but it will > impact > > WebAssembly correctness in all running modes. > > > > Cheers, > > Benjamin > > > > [1] > > http://searchfox.org/mozilla-central/source/js/src/devtools/automation/ > autospider.py > > _______________________________________________ > dev-tech-js-engine-internals mailing list > dev-tech-js-engine-internals@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals > _______________________________________________ dev-tech-js-engine-internals mailing list dev-tech-js-engine-internals@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
