> > Is there any reason to use V8_31BIT_SMIS_ON_64BIT_ARCH or not when not > using compressed pointers?
Smis are faster than any alternative, so 32-bit Smis potentially allow more code to benefit from the Smi advantage than 31-bit Smis. We separated the build flags mostly to be able to track the impact of moving to 31-bit Smis separately from the impact of un/compressing pointers on the fly. If you don't compress pointers, you're better served by 32-bit Smis. The difference should (in most cases) be small though, you might not even notice it. And just to reiterate: pointer compression requires 31-bit Smis, you can't have V8_COMPRESS_POINTERS without V8_31BIT_SMIS_ON_64BIT_ARCH. On Tue, Apr 14, 2020 at 5:56 PM Alex Kodat <alexko...@gmail.com> wrote: > It appears that the default for v8_enable_31bit_smis_on_64bit_arch has > changed from false to true somewhere between 7.7 (our last build for our > code) and 8.1 (what we're trying to upgrade to). It appears that if > V8_COMPRESS_POINTERS is defined, the setting of V8_31BIT_SMIS_ON_64BIT_ARCH > doesn't matter because kApiTaggedSize is set to kApiInt32Size in > v8-internal.h when V8_COMPRESS_POINTERS is defined. > > But, we decided we didn't want compressed pointers so we built V8 > with v8_enable_pointer_compression set to false. But, because we didn't > realize the default for v8_enable_31bit_smis_on_64bit_arch had changed to > true, when we compiled our code with V8_COMPRESS_POINTERS not defined, bad > things happened because V8_31BIT_SMIS_ON_64BIT_ARCH was defined for the V8 > build but not for our compile and when V8_COMPRESS_POINTERS is not defined > this difference causes problems. > > So this is mostly just a heads up to anyone building with > v8_enable_pointer_compression set to false. You either better also set > v8_enable_31bit_smis_on_64bit_arch to false in your V8 build or make sure > you define V8_31BIT_SMIS_ON_64BIT_ARCH in your own compiles. > > But then also, one question. Is there any reason to use > V8_31BIT_SMIS_ON_64BIT_ARCH or not when not using compressed pointers? It > seems that the difference is largely aesthetic -- what do you like your > SMIs to look like when looking at storage? So we just went with the new > default of V8_31BIT_SMIS_ON_64BIT_ARCH assuming the default must be the > better approach. ;-) Opinions? > > Thanks > > -- > -- -- v8-users mailing list v8-users@googlegroups.com http://groups.google.com/group/v8-users --- You received this message because you are subscribed to the Google Groups "v8-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to v8-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/v8-users/CAKSzg3StLqNNQV3Ysm6Xzq_m5CxepNT7YT6c9arkkV%2BXNNHH1g%40mail.gmail.com.
