DMD: Support D_SIMD

[p0nce]

Enabling core.simd:

• We can enable core.simd usage with DMD today, without even using D_SIMD, which brings the performance gap of LDC vs DMD from 20x to 4x. DMD binaries that makes heavy usage of intel-intrinsics typically go 5x faster.

Instead of the slow replacements. But does it support float2, int2? (EDIT: no, but we can work around it)

• D_SIMD and core.simd can be enabled with a constant
• MMX
• SSE
• SSE2 up to line: 1024
• SSE3
• SSSE3
• Wait for DMD 2.096 and test that _mm_movehl_ps generates MOVHLPS with __simd (and not MOVLPS)
• Wait for DMD 2.096 and test that _mm_movelh_ps generates MOVLHPS with __simd (and not MOVHPS)

[p0nce]

Also DMD: use core.simd instead of emulation when available.

[p0nce]

Blocked by #59

[p0nce]

Each version of DMD bring regressions when SIMD vectors are actually used. It's a maintenance burden.

[p0nce]

D_SIMD finally enabled in intel-intrinsics v1.9, when DMD 2.099+ is used. Let's see what happens next.

[p0nce]

8 hours later I was asked to remove it. 4 bugs are kinda blockers for D_SIMD to happen (well, more will be found as translation progress, but also perf will augment).

[p0nce]

4 more issues fixed by core.
https://forum.dlang.org/post/[email protected]

[p0nce]

Enable core.simd and D_SIMD usage in DMD now! It seems like the best time to do it. (mmm, not really)

[p0nce]

DMD debug builds now surprisingly useful since, they are at a 5% difference with LDC builds but build faster. Could become both faster to build and more efficient with a bit of effort on intel-intrinsics.

[p0nce]

Another final attemps at making D_SIMD used by default. Phew.

[p0nce]

It triggered only one regression, some Linux only bugs, and it seems like this is it? D_SIMD finally activated. (but not for AVX, only SSE)

[p0nce]

Some critical instructions:

• _mmcvtps_pd
• _mm_srli_epi32
• _mm_hadd_ps

[p0nce]

Besides, DMD output is wrong vs LDC on a complete plugin such as Lens.

[p0nce]

Critical for Lens:

• inlining of _mm_addsub_pd with D_SIMD => didn't work
• _mm_movelh_ps till buggy with D_SIMD? => no
• _mm_cvtepi32_ps
  (try within Lens regression testing, it's dangerous)

[p0nce]

Are we still in the DMD test suite? latest DMD fails in GH Actions => yes we are