Fix gradient behavior for min() and max() functions at boundaries. When input values are equal, the gradient is split evenly between both inputs. (#6411)

Co-authored-by: Yong He <yonghe@outlook.com>

4 files changed, 133 insertions, 63 deletions

diff --git a/tests/autodiff-dstdlib/dstdlib-max-min.slang b/tests/autodiff-dstdlib/dstdlib-max-min.slang
new file mode 100644
index 000000000..f37083706
--- /dev/null
+++ b/tests/autodiff-dstdlib/dstdlib-max-min.slang
@@ -0,0 +1,112 @@
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+typedef DifferentialPair<float> dpfloat;
+typedef DifferentialPair<float2> dpfloat2;
+
+[BackwardDifferentiable]
+float diffMax(float x, float y)
+{
+    return max(x, y);
+}
+
+[BackwardDifferentiable]
+float2 diffMax(float2 x, float2 y)
+{
+    return max(x, y);
+}
+
+[BackwardDifferentiable]
+float diffMin(float x, float y)
+{
+    return min(x, y);
+}
+
+[BackwardDifferentiable]
+float2 diffMin(float2 x, float2 y)
+{
+    return min(x, y);
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    // Test max() with x < y
+    {
+        dpfloat dpx = dpfloat(2.0, 1.0);
+        dpfloat dpy = dpfloat(5.0, -2.0);
+        dpfloat res = __fwd_diff(diffMax)(dpx, dpy);
+        outputBuffer[0] = res.p;        // Expect: 5.000000
+        outputBuffer[1] = res.d;        // Expect: -2.000000
+    }
+
+    // Test max() with x == y
+    {
+        dpfloat dpx = dpfloat(3.0, 1.0);
+        dpfloat dpy = dpfloat(3.0, -2.0);
+        dpfloat res = __fwd_diff(diffMax)(dpx, dpy);
+        outputBuffer[2] = res.p;        // Expect: 3.000000
+        outputBuffer[3] = res.d;        // Expect: -0.500000 (average of 1.0 and -2.0)
+    }
+
+    // Test min() with x > y
+    {
+        dpfloat dpx = dpfloat(5.0, 1.0);
+        dpfloat dpy = dpfloat(2.0, -2.0);
+        dpfloat res = __fwd_diff(diffMin)(dpx, dpy);
+        outputBuffer[4] = res.p;        // Expect: 2.000000
+        outputBuffer[5] = res.d;        // Expect: -2.000000
+    }
+
+    // Test min() with x == y
+    {
+        dpfloat dpx = dpfloat(3.0, 1.0);
+        dpfloat dpy = dpfloat(3.0, -2.0);
+        dpfloat res = __fwd_diff(diffMin)(dpx, dpy);
+        outputBuffer[6] = res.p;        // Expect: 3.000000
+        outputBuffer[7] = res.d;        // Expect: -0.500000 (average of 1.0 and -2.0)
+    }
+
+    // Test backward-mode max() with x == y
+    {
+        dpfloat dpx = dpfloat(3.0, 0.0);
+        dpfloat dpy = dpfloat(3.0, 0.0);
+        __bwd_diff(diffMax)(dpx, dpy, 1.0);
+        outputBuffer[8] = dpx.d;        // Expect: 0.500000 (half of gradient)
+        outputBuffer[9] = dpy.d;        // Expect: 0.500000 (half of gradient)
+    }
+
+    // Test backward-mode min() with x == y
+    {
+        dpfloat dpx = dpfloat(3.0, 0.0);
+        dpfloat dpy = dpfloat(3.0, 0.0);
+        __bwd_diff(diffMin)(dpx, dpy, 1.0);
+        outputBuffer[10] = dpx.d;       // Expect: 0.500000 (half of gradient)
+        outputBuffer[11] = dpy.d;       // Expect: 0.500000 (half of gradient)
+    }
+
+    // Test vector max() with x == y
+    {
+        dpfloat2 dpx = dpfloat2(float2(3.0, 4.0), float2(1.0, 2.0));
+        dpfloat2 dpy = dpfloat2(float2(3.0, 2.0), float2(-2.0, -3.0));
+        dpfloat2 res = __fwd_diff(diffMax)(dpx, dpy);
+        outputBuffer[12] = res.p[0];    // Expect: 3.000000
+        outputBuffer[13] = res.d[0];    // Expect: -0.500000 (average of 1.0 and -2.0)
+        outputBuffer[14] = res.p[1];    // Expect: 4.000000
+        outputBuffer[15] = res.d[1];    // Expect: 2.000000
+    }
+
+    // Test vector min() with x == y
+    {
+        dpfloat2 dpx = dpfloat2(float2(3.0, 4.0), float2(1.0, 2.0));
+        dpfloat2 dpy = dpfloat2(float2(3.0, 2.0), float2(-2.0, -3.0));
+        dpfloat2 res = __fwd_diff(diffMin)(dpx, dpy);
+        outputBuffer[16] = res.p[0];    // Expect: 3.000000
+        outputBuffer[17] = res.d[0];    // Expect: -0.500000 (average of 1.0 and -2.0)
+        outputBuffer[18] = res.p[1];    // Expect: 2.000000
+        outputBuffer[19] = res.d[1];    // Expect: -3.000000
+    }
+}
diff --git a/tests/autodiff-dstdlib/dstdlib-max-min.slang.expected.txt b/tests/autodiff-dstdlib/dstdlib-max-min.slang.expected.txt
new file mode 100644
index 000000000..504343b58
--- /dev/null
+++ b/tests/autodiff-dstdlib/dstdlib-max-min.slang.expected.txt
@@ -0,0 +1,21 @@
+type: float
+5.000000
+-2.000000
+3.000000
+-0.500000
+2.000000
+-2.000000
+3.000000
+-0.500000
+0.500000
+0.500000
+0.500000
+0.500000
+3.000000
+-0.500000
+4.000000
+2.000000
+3.000000
+-0.500000
+2.000000
+-3.000000
\ No newline at end of file
diff --git a/tests/autodiff-dstdlib/dstdlib-max.slang b/tests/autodiff-dstdlib/dstdlib-max.slang
deleted file mode 100644
index 026914c8c..000000000
--- a/tests/autodiff-dstdlib/dstdlib-max.slang
+++ /dev/null
@@ -1,52 +0,0 @@
-//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
-//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
-
-//TEST_INPUT:ubuffer(data=[0 0 0 0 0 0 0 0 0 0], stride=4):out,name=outputBuffer
-RWStructuredBuffer<float> outputBuffer;
-
-typedef DifferentialPair<float> dpfloat;
-typedef DifferentialPair<float2> dpfloat2;
-
-[BackwardDifferentiable]
-float diffMax(float x, float y)
-{
-    return max(x, y);
-}
-
-[BackwardDifferentiable]
-float2 diffMax(float2 x, float2 y)
-{
-    return max(x, y);
-}
-
-[numthreads(1, 1, 1)]
-void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
-{
-    {
-        dpfloat dpx = dpfloat(2.0, 1.0);
-        dpfloat dpy = dpfloat(5.0, -2.0);
-        dpfloat res = __fwd_diff(diffMax)(dpx, dpy);
-        outputBuffer[0] = res.p;        // Expect: 5.000000
-        outputBuffer[1] = res.d;        // Expect: -2.000000
-    }
-
-    {
-        dpfloat2 dpx = dpfloat2(float2(-3.0, 4.0), float2(-1.0, -1.0));
-        dpfloat2 dpy = dpfloat2(float2(1.0, 2.0), float2(2.0, 2.0));
-        dpfloat2 res = __fwd_diff(diffMax)(dpx, dpy);
-        outputBuffer[2] = res.p[0];     // Expect: 1.000000
-        outputBuffer[3] = res.d[0];     // Expect: 2.000000
-        outputBuffer[4] = res.p[1];     // Expect: 4.000000
-        outputBuffer[5] = res.d[1];     // Expect: -1.000000
-    }
-
-    {
-        dpfloat2 dpx = dpfloat2(float2(2.0, 3.0), float2(0.0, 0.0));
-        dpfloat2 dpy = dpfloat2(float2(5.0, 1.0), float2(0.0, 0.0));
-        __bwd_diff(diffMax)(dpx, dpy, float2(1.0, 2.0));
-        outputBuffer[6] = dpx.d[0]; // Expect: 0.000000
-        outputBuffer[7] = dpx.d[1]; // Expect: 2.000000
-        outputBuffer[8] = dpy.d[0]; // Expect: 1.000000
-        outputBuffer[9] = dpy.d[1]; // Expect: 0.000000
-    }
-}
diff --git a/tests/autodiff-dstdlib/dstdlib-max.slang.expected.txt b/tests/autodiff-dstdlib/dstdlib-max.slang.expected.txt
deleted file mode 100644
index 4cc1e9533..000000000
--- a/tests/autodiff-dstdlib/dstdlib-max.slang.expected.txt
+++ /dev/null
@@ -1,11 +0,0 @@
-type: float
-5.000000
--2.000000
-1.000000
-2.000000
-4.000000
--1.000000
-0.000000
-2.000000
-1.000000
-0.000000
\ No newline at end of file