Support custom derivatives of member functions of differentiable types (#5124)

* Initial work to support custom derivatives for member methods of differentiable types

* Support custom derivatives of member functions of differentiable types

 - Also adds support for declaring custom derivatives via extensions.

* Fix

* move defs

* Update slang-check-decl.cpp

* Create diff-member-func-custom-derivative.slang.expected.txt

* Update slang-check-decl.cpp

* Fix for static custom derivatives

* Fix diagnostics for [PreferRecompute]

* Add backward custom derivative tests

6 files changed, 181 insertions, 0 deletions

diff --git a/tests/autodiff/diff-member-func-custom-derivative.slang b/tests/autodiff/diff-member-func-custom-derivative.slang
new file mode 100644
index 000000000..4e4f540f9
--- /dev/null
+++ b/tests/autodiff/diff-member-func-custom-derivative.slang
@@ -0,0 +1,59 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+struct A : IDifferentiable
+{
+    float x;
+
+    [ForwardDerivative(diff_f)]
+    float f(float v)
+    {
+        return v * v;
+    }
+
+    static DifferentialPair<float> diff_f(DifferentialPair<A> dpa, DifferentialPair<float> v)
+    {
+        return diffPair(v.p * v.p, v.p * v.d * 2.0);
+    }
+
+    [BackwardDerivative(diff_g)]
+    float g(float v)
+    {
+        return v * v;
+    }
+
+    static void diff_g(inout DifferentialPair<A> dpa, inout DifferentialPair<float> v, float dOut)
+    {
+        v = diffPair(v.p, dOut * 2.0);
+    }
+}
+
+[ForwardDifferentiable]
+float test(A obj, float v)
+{
+    return obj.f(v);
+}
+
+[BackwardDifferentiable]
+float test2(A obj, float v)
+{
+    return obj.g(v);
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    A a = {0.0};
+    var p = diffPair(3.0, 1.0);
+    let rs = fwd_diff(test)(diffPair(a, {1.0}), p);
+
+    var q = diffPair(3.0);
+    var qa = diffPair(a);
+    bwd_diff(test2)(qa, q, 1.0);
+
+    outputBuffer[0] = rs.d;
+    outputBuffer[1] = q.d;
+}
diff --git a/tests/autodiff/diff-member-func-custom-derivative.slang.expected.txt b/tests/autodiff/diff-member-func-custom-derivative.slang.expected.txt
new file mode 100644
index 000000000..1bb28547d
--- /dev/null
+++ b/tests/autodiff/diff-member-func-custom-derivative.slang.expected.txt
@@ -0,0 +1,3 @@
+type: float
+6.000000
+2.000000
\ No newline at end of file
diff --git a/tests/autodiff/member-func-extension-custom-derivative.slang b/tests/autodiff/member-func-extension-custom-derivative.slang
new file mode 100644
index 000000000..8752dfff5
--- /dev/null
+++ b/tests/autodiff/member-func-extension-custom-derivative.slang
@@ -0,0 +1,55 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+struct A
+{
+    float x;
+
+    float f(float v)
+    {
+        return v * v;
+    }
+}
+
+extension A
+{
+    [ForwardDerivativeOf(f)]
+    DifferentialPair<float> diff_f(DifferentialPair<float> v)
+    {
+        return diffPair(v.p * v.p, v.p * v.d * 2.0);
+    }
+}
+
+struct Foo<T : IDifferentiable>
+{
+    T value;
+    T doThing() { return value; }
+}
+
+extension<T : IDifferentiable> Foo<T>
+{
+    [ForwardDerivativeOf(doThing)]
+    DifferentialPair<T> diff_doThing()
+    {
+        return diffPair(value, T.dzero());
+    }
+}
+
+
+[ForwardDifferentiable]
+float test(Foo<float> obj, float v)
+{
+    return obj.doThing() * v;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    Foo<float> a = {0.0};
+    var p = diffPair(3.0, 1.0);
+    let rs = __fwd_diff(test)(a, p);
+    outputBuffer[0] = rs.d;
+}
diff --git a/tests/autodiff/member-func-extension-custom-derivative.slang.expected.txt b/tests/autodiff/member-func-extension-custom-derivative.slang.expected.txt
new file mode 100644
index 000000000..4b1f4c0d9
--- /dev/null
+++ b/tests/autodiff/member-func-extension-custom-derivative.slang.expected.txt
@@ -0,0 +1,2 @@
+type: float
+0.000000
diff --git a/tests/autodiff/static-func-custom-derivative.slang b/tests/autodiff/static-func-custom-derivative.slang
new file mode 100644
index 000000000..b75012735
--- /dev/null
+++ b/tests/autodiff/static-func-custom-derivative.slang
@@ -0,0 +1,59 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+struct A : IDifferentiable
+{
+    float x;
+
+    [ForwardDerivative(diff_f)]
+    static float f(float v)
+    {
+        return v * v;
+    }
+
+    static DifferentialPair<float> diff_f(DifferentialPair<float> v)
+    {
+        return diffPair(v.p * v.p, v.p * v.d * 2.0);
+    }
+
+    [BackwardDerivative(diff_g)]
+    static float g(float v)
+    {
+        return v * v;
+    }
+
+    static void diff_g(inout DifferentialPair<float> v, float.Differential dOut)
+    {
+        v = diffPair(v.p, dOut * 2.0);
+    }
+}
+
+[ForwardDifferentiable]
+float test(A obj, float v)
+{
+    return obj.f(v);
+}
+
+[BackwardDifferentiable]
+float test2(A obj, float v)
+{
+    return obj.g(v);
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    A a = {0.0};
+    var p = diffPair(3.0, 1.0);
+    let rs = fwd_diff(test)(diffPair(a, {1.0}), p);
+
+    var q = diffPair(3.0);
+    var qa = diffPair(a);
+    bwd_diff(test2)(qa, q, 1.0);
+
+    outputBuffer[0] = rs.d;
+    outputBuffer[1] = q.d;
+}
diff --git a/tests/autodiff/static-func-custom-derivative.slang.expected.txt b/tests/autodiff/static-func-custom-derivative.slang.expected.txt
new file mode 100644
index 000000000..1bb28547d
--- /dev/null
+++ b/tests/autodiff/static-func-custom-derivative.slang.expected.txt
@@ -0,0 +1,3 @@
+type: float
+6.000000
+2.000000
\ No newline at end of file