Miscellaneous backward autodiff fixes. (#2665)

* Fix differentiable type registration

* Fix use of non-differentiable return value in a differentiable func.

* Fix use of primal inst that does not dominate the diff block.

* Fix primal inst hoisting, and add missing type legalization logic.

* Make `detach` defined on all differentiable T.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

8 files changed, 127 insertions, 9 deletions

diff --git a/tests/autodiff/bool-return-control-flow.slang b/tests/autodiff/bool-return-control-flow.slang
new file mode 100644
index 000000000..9dd398a89
--- /dev/null
+++ b/tests/autodiff/bool-return-control-flow.slang
@@ -0,0 +1,31 @@
+//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 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[BackwardDifferentiable]
+bool conditionFunc(no_diff float a, inout float x)
+{
+    x = x * a;
+    return x > 100.f;
+}
+
+[BackwardDifferentiable]
+float outerFunc(no_diff float a, float x)
+{
+    if (conditionFunc(a, x))
+        return x;
+    else
+        return -x;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    float a = 10.0;
+    DifferentialPair<float> dpx = DifferentialPair<float>(4.f, 1.f);
+    __bwd_diff(outerFunc)(a, dpx, 1.0);
+
+    outputBuffer[0] = dpx.d;
+}
\ No newline at end of file
diff --git a/tests/autodiff/bool-return-control-flow.slang.expected.txt b/tests/autodiff/bool-return-control-flow.slang.expected.txt
new file mode 100644
index 000000000..e2789a12c
--- /dev/null
+++ b/tests/autodiff/bool-return-control-flow.slang.expected.txt
@@ -0,0 +1,5 @@
+type: float
+-10.000000
+0.000000
+0.000000
+0.000000
\ No newline at end of file
diff --git a/tests/autodiff/reverse-control-flow-2.slang b/tests/autodiff/reverse-control-flow-2.slang
new file mode 100644
index 000000000..cde707b4d
--- /dev/null
+++ b/tests/autodiff/reverse-control-flow-2.slang
@@ -0,0 +1,75 @@
+//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 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[BackwardDifferentiable]
+bool doWork(float x, out float y)
+{
+    bool retVal = false;
+    y = 0;
+    for (;;)
+    {
+        if (x == 0.0)
+            break;
+
+        bool exited = (x == 1.0);
+
+        y += x;
+
+        if (!exited)
+        {
+            if (x < 1.0)
+            {
+                float b = x * 2.0f;
+                y += b;
+                exited = true;
+            }
+        }
+        retVal = true;
+        break;
+    }
+    return retVal;
+}
+
+[BackwardDifferentiable]
+bool doWork2(float x, out float y)
+{
+    y = 0;
+
+    if (x == 0.0) return false;
+
+    [ForceUnroll]
+    for (int i = 0; i < 2; ++i)
+    {
+        if (x > 0.0)
+        {
+            y += x;
+
+            if (x == 1.0) break;
+
+            y += x;
+        }
+        else
+        {
+            y += x;
+        }
+    }
+    return true;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    {
+        var dpx = diffPair(0.5f, 1.0f);
+        __bwd_diff(doWork)(dpx, 1.0f);
+        outputBuffer[0] = dpx.d;
+    }
+    {
+        var dpx = diffPair(0.5f, 0.0f);
+        __bwd_diff(doWork2)(dpx, 1.0);
+        outputBuffer[1] = dpx.d;
+    }
+}
diff --git a/tests/autodiff/reverse-control-flow-2.slang.expected.txt b/tests/autodiff/reverse-control-flow-2.slang.expected.txt
new file mode 100644
index 000000000..31023ed32
--- /dev/null
+++ b/tests/autodiff/reverse-control-flow-2.slang.expected.txt
@@ -0,0 +1,6 @@
+type: float
+3.000000
+4.000000
+0.000000
+0.000000
+0.000000
diff --git a/tests/diagnostics/autodiff-data-flow-2.slang b/tests/diagnostics/autodiff-data-flow-2.slang
index aa923c5d6..3148c6a41 100644
--- a/tests/diagnostics/autodiff-data-flow-2.slang
+++ b/tests/diagnostics/autodiff-data-flow-2.slang
@@ -24,5 +24,11 @@ float h(float x)
     float val = 0;
     // no diagnostic by clarifying intention.
     val = no_diff(f(x + 1));
+
+    // error: dynamic loop without [MaxIters] or [ForceUnroll]
+    for (int i = 0; i < (int)x; i++)
+    {
+    }
+
     return val;
 }
diff --git a/tests/diagnostics/autodiff-data-flow-2.slang.expected b/tests/diagnostics/autodiff-data-flow-2.slang.expected
index 9026c0748..725a27c9c 100644
--- a/tests/diagnostics/autodiff-data-flow-2.slang.expected
+++ b/tests/diagnostics/autodiff-data-flow-2.slang.expected
@@ -1,8 +1,11 @@
 result code = -1
 standard error = {
-tests/diagnostics/autodiff-data-flow-2.slang(18): error 41020: derivative cannot be propagated through call to non-backward-differentiable function `f`, use 'no_diff' to clarify intention.
+tests/diagnostics/autodiff-data-flow-2.slang(17): error 41020: derivative cannot be propagated through call to non-backward-differentiable function `f`, use 'no_diff' to clarify intention.
     float val = f(x + 1); // Error: f must also be backward-differentiable
                  ^
+tests/diagnostics/autodiff-data-flow-2.slang(29): error 30510: loops inside a differentiable function need to provide either '[MaxIters(n)]' or '[ForceUnroll]' attribute.
+    for (int i = 0; i < (int)x; i++)
+    ^~~
 }
 standard output = {
 }
diff --git a/tests/diagnostics/autodiff.slang b/tests/diagnostics/autodiff.slang
index 935ef07cb..7905b48b6 100644
--- a/tests/diagnostics/autodiff.slang
+++ b/tests/diagnostics/autodiff.slang
@@ -12,11 +12,6 @@ float f(float x)
     if (x > 5)
         val = x + 1;
 
-    // warning: dynamic loop without [MaxIters] or [ForceUnroll]
-    for (int i = 0; i < (int)x; i++) 
-    {
-    }
-
     [MaxIters(2)]
     for (int i = 0; i < (int)x; i++) // OK
     {
diff --git a/tests/diagnostics/autodiff.slang.expected b/tests/diagnostics/autodiff.slang.expected
index 952503d1c..d075b9406 100644
--- a/tests/diagnostics/autodiff.slang.expected
+++ b/tests/diagnostics/autodiff.slang.expected
@@ -1,8 +1,5 @@
 result code = -1
 standard error = {
-tests/diagnostics/autodiff.slang(16): error 30510: loops inside a differentiable function need to provide either '[MaxIters(n)]' or '[ForceUnroll]' attribute.
-    for (int i = 0; i < (int)x; i++)
-    ^~~
 tests/diagnostics/autodiff.slang(35): error 38031: 'no_diff' can only be used to decorate a call.
     float x1 = no_diff x; // invalid use of no_diff here.
                ^~~~~~~