From b282c88d9743fc9bb60ef27cfa5d9cf58cccd60b Mon Sep 17 00:00:00 2001 From: Copilot <198982749+Copilot@users.noreply.github.com> Date: Thu, 3 Jul 2025 23:53:02 -0700 Subject: Make copysign function differentiable (#7585) * Initial plan * Implement copysign forward and backward derivatives Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com> * Fix copysign test format to use expected.txt file Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com> * Add wgsl support to copysign and fix y==0 derivative case Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com> * Add wgsl support to copysign helper functions Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com> * Fix copysign derivative to return 0 when either x or y is 0 Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com> --- source/slang/diff.meta.slang | 77 ++++++++++++++++++++++++++++++++++++++++++++ source/slang/hlsl.meta.slang | 10 +++--- 2 files changed, 82 insertions(+), 5 deletions(-) (limited to 'source/slang') diff --git a/source/slang/diff.meta.slang b/source/slang/diff.meta.slang index 13c5d2d47..542983049 100644 --- a/source/slang/diff.meta.slang +++ b/source/slang/diff.meta.slang @@ -2160,6 +2160,83 @@ void __d_min(inout DifferentialPair dpx, inout DifferentialPair dpy, T.Dif VECTOR_MATRIX_BINARY_DIFF_IMPL(min) +// copysign +__generic +[BackwardDifferentiable] +[PreferRecompute] +[ForwardDerivativeOf(copysign)] +DifferentialPair __d_copysign(DifferentialPair dpx, DifferentialPair dpy) +{ + // copysign(x, y) = sign(y) * abs(x) + // d/dx copysign(x, y) = sign(y) * sign(x) when x != 0 and y != 0, 0 when x == 0 or y == 0 + // d/dy copysign(x, y) = 0 (sign function is not differentiable w.r.t y) + let sign_y = select(dpy.p >= T(0.0), T(1.0), T(-1.0)); + let sign_x = select(dpx.p >= T(0.0), T(1.0), T(-1.0)); + // When x == 0 or y == 0, derivative w.r.t. x should be 0 + let dx_coeff = select((dpx.p == T(0.0)) || (dpy.p == T(0.0)), T(0.0), sign_y * sign_x); + return DifferentialPair( + copysign(dpx.p, dpy.p), + __mul_p_d(dx_coeff, dpx.d) + ); +} + +__generic +[BackwardDifferentiable] +[PreferRecompute] +[BackwardDerivativeOf(copysign)] +void __d_copysign(inout DifferentialPair dpx, inout DifferentialPair dpy, T.Differential dOut) +{ + let sign_y = select(dpy.p >= T(0.0), T(1.0), T(-1.0)); + let sign_x = select(dpx.p >= T(0.0), T(1.0), T(-1.0)); + // When x == 0 or y == 0, derivative w.r.t. x should be 0 + let dx_coeff = select((dpx.p == T(0.0)) || (dpy.p == T(0.0)), T(0.0), sign_y * sign_x); + // Gradient flows only to x since d/dy copysign = 0 + dpx = diffPair(dpx.p, __mul_p_d(dx_coeff, dOut)); + dpy = diffPair(dpy.p, T.dzero()); +} + +__generic +[BackwardDifferentiable] +[PreferRecompute] +[ForwardDerivativeOf(copysign)] +DifferentialPair> __d_copysign_vector( + DifferentialPair> dpx, DifferentialPair> dpy) +{ + vector result; + vector.Differential d_result; + [ForceUnroll] for (int i = 0; i < N; ++i) + { + DifferentialPair dp_elem = __d_copysign( + DifferentialPair(dpx.p[i], __slang_noop_cast(dpx.d[i])), + DifferentialPair(dpy.p[i], __slang_noop_cast(dpy.d[i]))); + result[i] = dp_elem.p; + d_result[i] = __slang_noop_cast(dp_elem.d); + } + return DifferentialPair>(result, d_result); +} + +__generic +[BackwardDifferentiable] +[PreferRecompute] +[BackwardDerivativeOf(copysign)] +void __d_copysign_vector( + inout DifferentialPair> dpx, + inout DifferentialPair> dpy, + vector.Differential dOut) +{ + vector.Differential x_d_result, y_d_result; + [ForceUnroll] for (int i = 0; i < N; ++i) + { + DifferentialPair x_dp = DifferentialPair(dpx.p[i], __slang_noop_cast(dpx.d[i])); + DifferentialPair y_dp = DifferentialPair(dpy.p[i], __slang_noop_cast(dpy.d[i])); + __d_copysign(x_dp, y_dp, __slang_noop_cast(dOut[i])); + x_d_result[i] = __slang_noop_cast(x_dp.d); + y_d_result[i] = __slang_noop_cast(y_dp.d); + } + dpx = diffPair(dpx.p, x_d_result); + dpy = diffPair(dpy.p, y_d_result); +} + // Lerp __generic [BackwardDifferentiable] diff --git a/source/slang/hlsl.meta.slang b/source/slang/hlsl.meta.slang index 38f274984..7879fc493 100644 --- a/source/slang/hlsl.meta.slang +++ b/source/slang/hlsl.meta.slang @@ -7685,7 +7685,7 @@ matrix ceil(matrix x) /// @category math __generic [__readNone] -[require(cpp_cuda_glsl_hlsl_metal_spirv)] +[require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl)] vector copysign_half(vector x, vector y) { let ux = reinterpret>(x); @@ -7702,7 +7702,7 @@ vector copysign_half(vector x, vector y) /// @category math __generic [__readNone] -[require(cpp_cuda_glsl_hlsl_metal_spirv)] +[require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl)] vector copysign_float(vector x, vector y) { let ux = reinterpret>(x); @@ -7719,7 +7719,7 @@ vector copysign_float(vector x, vector y) /// @category math __generic [__readNone] -[require(cpp_cuda_glsl_hlsl_metal_spirv)] +[require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl)] vector copysign_double(vector x, vector y) { let ux = reinterpret>(x); @@ -7740,7 +7740,7 @@ vector __real_cast(vector val); /// @category math __generic [__readNone] -[require(cpp_cuda_glsl_hlsl_metal_spirv)] +[require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl)] vector copysign(vector x, vector y) { __target_switch @@ -7766,7 +7766,7 @@ vector copysign(vector x, vector y) __generic [__readNone] -[require(cpp_cuda_glsl_hlsl_metal_spirv)] +[require(cpp_cuda_glsl_hlsl_metal_spirv_wgsl)] T copysign(T x, T y) { __target_switch -- cgit v1.2.3