Stream: git-wasmtime

Topic: wasmtime / PR #1990 Implement fcvt_to_uint_sat (f32x4 -> ...

Wasmtime GitHub notifications bot (Jul 07 2020 at 17:40):

abrown opened PR #1990 from trunc-sat-unsigned-again to main:

This replaces #1822; it consists of the same functionality but removes the AVX512 instruction lowering for the time being. There are two reasons for this:

• the default MXCSR rounding is round to nearest even, which does not match the semantics required by i32x4.trunc_sat_f32x4_u. We can then use embedded rounding control but lose the ability to specify the vector length, so the instruction would operate on 512-bits which we should discuss (@sunfishcode has reported issues with 512-bit vectors in Spidermonkey)
• the output of VCVTPS2UDQ for negative lanes is 0xFFFFFFFF (I had thought it would be 0x00000000); this can be resolved with the following sequence: v0 = pxor ...; v2 = fcmp gte v1, v0 (gte ensures they are ordered); v3 = vcvtps2udq v1; v4 = band v2, v3. However, I would like to look at this a little bit more before submitting a separate PR for it (this is the reason for keeping the legalization in enc_tables.rs and under narrow_avx, BTW).

Wasmtime GitHub notifications bot (Jul 07 2020 at 17:43):

abrown requested julian-seward1 for a review on PR #1990.

Wasmtime GitHub notifications bot (Jul 08 2020 at 16:02):

abrown updated PR #1990 from trunc-sat-unsigned-again to main:

This replaces #1822; it consists of the same functionality but removes the AVX512 instruction lowering for the time being. There are two reasons for this:

• the default MXCSR rounding is round to nearest even, which does not match the semantics required by i32x4.trunc_sat_f32x4_u. We can then use embedded rounding control but lose the ability to specify the vector length, so the instruction would operate on 512-bits which we should discuss (@sunfishcode has reported issues with 512-bit vectors in Spidermonkey)
• the output of VCVTPS2UDQ for negative lanes is 0xFFFFFFFF (I had thought it would be 0x00000000); this can be resolved with the following sequence: v0 = pxor ...; v2 = fcmp gte v1, v0 (gte ensures they are ordered); v3 = vcvtps2udq v1; v4 = band v2, v3. However, I would like to look at this a little bit more before submitting a separate PR for it (this is the reason for keeping the legalization in enc_tables.rs and under narrow_avx, BTW).

Wasmtime GitHub notifications bot (Jul 08 2020 at 16:11):

julian-seward1 submitted PR Review.

Wasmtime GitHub notifications bot (Jul 08 2020 at 16:19):

abrown updated PR #1990 from trunc-sat-unsigned-again to main:

This replaces #1822; it consists of the same functionality but removes the AVX512 instruction lowering for the time being. There are two reasons for this:

• the default MXCSR rounding is round to nearest even, which does not match the semantics required by i32x4.trunc_sat_f32x4_u. We can then use embedded rounding control but lose the ability to specify the vector length, so the instruction would operate on 512-bits which we should discuss (@sunfishcode has reported issues with 512-bit vectors in Spidermonkey)
• the output of VCVTPS2UDQ for negative lanes is 0xFFFFFFFF (I had thought it would be 0x00000000); this can be resolved with the following sequence: v0 = pxor ...; v2 = fcmp gte v1, v0 (gte ensures they are ordered); v3 = vcvtps2udq v1; v4 = band v2, v3. However, I would like to look at this a little bit more before submitting a separate PR for it (this is the reason for keeping the legalization in enc_tables.rs and under narrow_avx, BTW).

Wasmtime GitHub notifications bot (Jul 08 2020 at 17:20):

abrown merged PR #1990.

Last updated: Oct 23 2024 at 20:03 UTC