vecmath: native WebAssembly SIMD128 backend

[borisbat]

Behavior change: on the web build int(x) of a float outside the 32-bit range now saturates (NaN gives 0) instead of answering INT_MIN - the NEON contract; nothing to do unless a script relied on the sentinel.

Why. The web build ran vecmath's SSE2 arm through emscripten's -msse2 compat layer. There a float-to-int conversion is a per-lane lrint loop (86 wasm instructions for v_cvti_vec4i, 170 for v_cvt_roundi, 91 for v_floor), and min, max, select, abs and mul+add each cost two to four ops.

What changes.

• include/vecmath/dag_vecMath_wasm.h implements the backend contract on wasm SIMD128: trunc_sat, floor/nearest, pmin/pmax with swapped operands (the SSE NaN and signed-zero rule), bitselect, one i8x16.shuffle per permutation.
• vec4f/vec4i are clang typed vectors, selected on __wasm_simd128__ ahead of the __SSE2__ the compat layer predefines; daScriptC.h spells the same types for C.
• web/ and the dasImgui wasm archives drop -msse2; relaxed SIMD is an opt-in knob, OFF because Safari refuses any relaxed opcode.
• The backend battery gains a wasm arm and rows for the saturating converts, the pshufb key mask, the 64-bit shifts and other previously unpinned primitives; the wasm_build lane builds both arms and runs them under node.
• The dasAudio convolution reverb takes its SIMD path on wasm; dasStbImage no longer forces its scalar paths there. Both were gated on the removed -msse2.

Observable behavior.

• interpreter under node, float-to-int + floor + round loop: 26.4 ms -> 11.9 ms; n-bodies and the other profile samples unchanged
• int(3e9) on the web build: INT_MIN -> INT_MAX (saturating, as on NEON)
• daslang_static.wasm carries no relaxed opcode before or after

Where to look. The operand swap in v_min/v_max, the sign-bit shift in v_sel, the shift-count guards, and vd_cvt_to_vec4i's lane join in dag_vecMath_double.h.

Validation, claims, ledger

Validation

• The wasm arm can fail only in .github/workflows/wasm_build.yml job wasm_build (the native ctest -L small builds the same file with EXPECT_WASM undefined). Ran on Windows, one of the three matrix cells, in web/cmake_temp: ninja test_vecmath_native test_vecmath_scalar, then from web/: "$EMSDK_NODE" --experimental-wasm-exnref output/tests/test_vecmath_native.js and ..._scalar.js - both all vecmath backend checks passed, exit 0; "$EMSDK_NODE" --experimental-wasm-exnref test/dastest_wasm.js ../ ./output - 1696 passed, 0 failed. EMSDK_PYTHON pointed at python 3.13 (the emsdk-bundled 3.9 is below emscripten's floor). Linux and macOS cells: the lane's run on the head commit.
• Native: full MSVC Release build, ctest -C Release -L small 150 passed (includes vecmath_native and vecmath_scalar, rerun after the new rows), dastest --test tests/language 1758 passed. The preflight tests lane selected nothing (no .das changed) and the full preflight chain was not run: the diff reaches only the wasm lane and the vecmath headers, whose x86 and NEON arms gain preprocessor gates and no code.
• No relaxed opcode in the built module: llvm-objdump -d daslang_static.wasm | grep -c relaxed is 0 for both the baseline and this branch.
• Woodpecker round on 9eb6980: one P2 finding (the test targets' link options dropped the memory64 and pthread link flags), fixed; no second round - the fix batch is build plumbing, two preprocessor gates and test rows.

Claims - stated, not tested

• The dasAudio convolution reverb's SIMD path and dasStbImage's wasm SIMD paths compile and run on wasm: verified by the web build and the node suite, not by an audio or image test under node. A break would be a compile error in libDasModuleAudio / libDasModuleStbImage on the wasm_build lane or a wrong reverb/decode result in the playground.
• DAS_WASM_MEMORY64=ON / DAS_WASM_PTHREADS=ON builds of the two test arms link: the link option list carries -sMEMORY64=2 / -pthread from the same knobs, not built here.
• The relaxed-SIMD arm of v_madd/v_nmsub (-mrelaxed-simd, opt-in) compiles: built by hand once for the instruction-count probe, no lane builds it.

Not done

• Upstream contribution of dag_vecMath_wasm.h to DagorEngine prog/1stPartyLibs/vecmath after this lands.
• Declined folds from the dupe audit: sharing the __builtin_shufflevector perm block with the NEON arm, moving the v_hmin/v_check_*/v_round family into dag_vecMath_common.h, and the vd_dot* one-liners into the double header's shared tail - each touches the other backends' arms, which go upstream as they are.
• The target auto-detect ladder stays duplicated between dag_vecMathDecl.h and daScriptC.h (pre-existing; a shared C-compatible header is the fold).
• web/ has no ARCHITECTURE.md; its README.md cannot take anchored facts, so web/CMakeLists.txt's why-comments stay comments.
• The JIT's wasm feature string (+simd128,+nontrapping-fptoint) is unchanged; JIT-emitted code keeps mul+add, matching the runtime archive.

[Copilot]

🟡 Changes recommended

Vecmath README updates are missing the -mnontrapping-fptoint requirement even though the wasm backend depends on trunc_sat conversions enabled by that feature.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Adds a native WebAssembly SIMD128 backend for vecmath (replacing reliance on Emscripten’s SSE2 compatibility layer), updates wasm build flags accordingly, and extends CI/tests/docs to validate and explain the new wasm SIMD behavior (notably saturating float→int conversions on web builds).

Changes:

• Implement include/vecmath/dag_vecMath_wasm.h and wire _TARGET_SIMD_WASM auto-detect + vec4d support for wasm.
• Drop -msse2 from web/ and dasImgui wasm builds; add an opt-in -mrelaxed-simd knob (default OFF for Safari compatibility).
• Extend vecmath backend battery + wasm CI lane to run wasm-native and scalar arms under Node.

File summaries

File	Description
web/REVIEW.md	Adds checklist constraints around relaxed-SIMD defaults and keeping wasm feature flags in sync with dasImgui.
web/CMakeLists.txt	Removes -msse2, adds DAS_WASM_RELAXED_SIMD option and -mrelaxed-simd gating.
tests-cpp/REVIEW.md	Clarifies “big” checklist applicability based on ctest labels rather than local CMake ownership.
tests-cpp/big/vecmath_backend/test_vecmath_backend.cpp	Updates backend battery semantics/guards for wasm (packed _x ops + saturating converts) and adds new pinned rows.
tests-cpp/big/vecmath_backend/CMakeLists.txt	Ensures wasm builds explicitly build/link the vecmath test arms into web/output/tests with appropriate link options.
skills/internal/preflight.md	Updates documentation of wasm_build.yml to include the Node-run language suite + vecmath battery.
skills/comment_style_hygiene.md	Adds a rule about preserving upstream comment/shape conventions for upstream-contributed code.
modules/dasStbImage/CMakeLists.txt	Removes wasm-only scalar-forcing defines now that -msse2 is no longer used on web builds.
modules/dasImgui/REVIEW.md	Mirrors relaxed-SIMD “default OFF” constraints and cross-folder flag sync requirements.
modules/dasImgui/CMakeLists.txt	Drops -msse2 and adds opt-in relaxed-SIMD flag for wasm archives.
modules/dasAudio/src/convolution_reverb.h	Enables wasm SIMD path via _TARGET_SIMD_WASM gating.
include/vecmath/usage.md	Updates vecmath usage docs to include wasm SIMD128 among supported backends.
include/vecmath/README.md	Updates high-level README to include wasm SIMD128 in supported targets and describes wasm flags (see review comment re: -mnontrapping-fptoint).
include/vecmath/dag_vecMathDecl.h	Adds _TARGET_SIMD_WASM auto-detect and wasm typed-vector definitions for vec4f/vec4i/vec4d.
include/vecmath/dag_vecMath.h	Includes the new wasm backend header when _TARGET_SIMD_WASM is selected.
include/vecmath/dag_vecMath_wasm.h	New wasm SIMD128 backend implementing vecmath primitive contract (including saturating float→int).
include/vecmath/dag_vecMath_double.h	Adds wasm SIMD128 implementation for the vec4d layer.
include/vecmath/dag_vecMath_const.h	Extends constant definitions to cover the wasm backend.
include/vecmath/dag_vecMath_common.h	Aligns shared helpers to treat wasm like SSE where semantics match.
include/vecmath/CLAUDE.md	Updates module overview and backend contract notes to include wasm.
include/daScript/daScriptC.h	Mirrors wasm target auto-detect and defines wasm vec4f/vec4i types for the C API.
CMakeLists.txt	Adds the new vecmath wasm header to the build’s vecmath source list.
.github/workflows/wasm_build.yml	Builds vecmath test arms explicitly and runs vecmath battery + language suite under Node.
.github/workflows/REVIEW.md	Tightens workflow-doc update requirements (row + per-workflow section in skills/internal/preflight.md).

Review details

• Files reviewed: 24/24 changed files
• Comments generated: 1
• Review effort level: Lite

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