Fixed derivatives for kIROp_Neg and kIROp_Div, added another test (#2639)

4 files changed, 134 insertions, 0 deletions

diff --git a/source/slang/slang-ir-autodiff-fwd.cpp b/source/slang/slang-ir-autodiff-fwd.cpp
index a45a3abf9..04acad435 100644
--- a/source/slang/slang-ir-autodiff-fwd.cpp
+++ b/source/slang/slang-ir-autodiff-fwd.cpp
@@ -1329,9 +1329,12 @@ InstPair ForwardDiffTranscriber::transcribeInstImpl(IRBuilder* builder, IRInst*
         return transcribeSwizzle(builder, as<IRSwizzle>(origInst));
     
     case kIROp_MakeTuple:
+    case kIROp_Neg:
         return transcribeByPassthrough(builder, origInst);
+
     case kIROp_UpdateElement:
         return transcribeUpdateElement(builder, origInst);
+
     case kIROp_unconditionalBranch:
         return transcribeControlFlow(builder, origInst);
 
@@ -1346,6 +1349,7 @@ InstPair ForwardDiffTranscriber::transcribeInstImpl(IRBuilder* builder, IRInst*
     case kIROp_FieldExtract:
     case kIROp_FieldAddress:
         return transcribeFieldExtract(builder, origInst);
+
     case kIROp_GetElement:
     case kIROp_GetElementPtr:
         return transcribeGetElement(builder, origInst);
@@ -1361,12 +1365,15 @@ InstPair ForwardDiffTranscriber::transcribeInstImpl(IRBuilder* builder, IRInst*
 
     case kIROp_MakeDifferentialPair:
         return transcribeMakeDifferentialPair(builder, as<IRMakeDifferentialPair>(origInst));
+
     case kIROp_DifferentialPairGetPrimal:
     case kIROp_DifferentialPairGetDifferential:
         return transcribeDifferentialPairGetElement(builder, origInst);
+
     case kIROp_ExtractExistentialValue:
     case kIROp_MakeExistential:
         return transcribeSingleOperandInst(builder, origInst);
+
     case kIROp_ExtractExistentialType:
     {
         IRInst* witnessTable;
@@ -1377,8 +1384,10 @@ InstPair ForwardDiffTranscriber::transcribeInstImpl(IRBuilder* builder, IRInst*
     }
     case kIROp_ExtractExistentialWitnessTable:
         return transcribeExtractExistentialWitnessTable(builder, origInst);
+
     case kIROp_WrapExistential:
         return transcribeWrapExistential(builder, origInst);
+
     case kIROp_undefined:
         return transcribeUndefined(builder, origInst);
 
@@ -1387,8 +1396,10 @@ InstPair ForwardDiffTranscriber::transcribeInstImpl(IRBuilder* builder, IRInst*
         // so we treat this inst as non differentiable.
         // We can extend the frontend and IR with a separate op-code that can provide an explicit diff value.
         return trascribeNonDiffInst(builder, origInst);
+
     case kIROp_StructKey:
         return InstPair(origInst, nullptr);
+        
     case kIROp_Unreachable:
     {
         auto unreachInst = builder->emitUnreachable();
diff --git a/source/slang/slang-ir-autodiff-transpose.h b/source/slang/slang-ir-autodiff-transpose.h
index eef820804..d9b28ea3c 100644
--- a/source/slang/slang-ir-autodiff-transpose.h
+++ b/source/slang/slang-ir-autodiff-transpose.h
@@ -1247,6 +1247,8 @@ struct DiffTransposePass
             case kIROp_Add:
             case kIROp_Mul:
             case kIROp_Sub: 
+            case kIROp_Div: 
+            case kIROp_Neg:
                 return transposeArithmetic(builder, fwdInst, revValue);
 
             case kIROp_Call:
@@ -1927,6 +1929,41 @@ struct DiffTransposePass
                     SLANG_ASSERT_FAILURE("Neither operand of a mul instruction is a differential inst");
                 }
             }   
+            case kIROp_Div: 
+            {
+                if (isDifferentialInst(fwdInst->getOperand(0)))
+                {
+                    SLANG_RELEASE_ASSERT(!isDifferentialInst(fwdInst->getOperand(1)));
+
+                    // (Out = dA / B) -> (dA += dOut / B)
+                    return TranspositionResult(
+                        List<RevGradient>(
+                            RevGradient(
+                                fwdInst->getOperand(0),
+                                builder->emitDiv(operandType, revValue, fwdInst->getOperand(1)),
+                                fwdInst)));
+                }
+                {
+                    SLANG_ASSERT_FAILURE("The first operand of a div inst must be a differential inst");
+                }
+            }
+            case kIROp_Neg: 
+            {
+                if (isDifferentialInst(fwdInst->getOperand(0)))
+                {
+                    // (Out = -dA) -> (dA += -dOut)
+                    return TranspositionResult(
+                        List<RevGradient>(
+                            RevGradient(
+                                fwdInst->getOperand(0),
+                                builder->emitNeg(operandType, revValue),
+                                fwdInst)));
+                }
+                else
+                {
+                    SLANG_ASSERT_FAILURE("Cannot transpose neg of a non-differentiable inst");
+                }
+            }   
 
             default:
                 SLANG_ASSERT_FAILURE("Unhandled arithmetic");
diff --git a/tests/autodiff/reverse-arithmetic.slang b/tests/autodiff/reverse-arithmetic.slang
new file mode 100644
index 000000000..4e13251e4
--- /dev/null
+++ b/tests/autodiff/reverse-arithmetic.slang
@@ -0,0 +1,78 @@
+//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 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+typedef DifferentialPair<float> dpfloat;
+typedef float.Differential dfloat;
+
+[BackwardDifferentiable]
+float f(float x)
+{
+    return x;
+}
+
+[BackwardDifferentiable]
+float h(float x, float y)
+{
+    float m = x + y;
+    float n = x - y;
+    return m * n + 2 * x * y;
+}
+
+[BackwardDifferentiable]
+float j(float x, float y)
+{
+    float m = x / y;
+    return m * y;
+}
+
+[BackwardDifferentiable]
+float k(float x, float y)
+{
+    float m = -x;
+    return m * y;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    {
+        dpfloat dpa = dpfloat(2.0, 1.0);
+
+        __bwd_diff(f)(dpa, 1.0);
+
+        outputBuffer[0] = dpa.d; // Expect: 1
+    }
+
+    {
+        dpfloat dpa = dpfloat(2.0, 1.0);
+        dpfloat dpb = dpfloat(1.5, 1.0);
+
+        __bwd_diff(h)(dpa, dpb, 1.0);
+
+        outputBuffer[1] = dpa.d; // Expect: (2 * 2.0) + (2 * 1.5) = 7.0
+        outputBuffer[2] = dpb.d; // Expect: -(2 * 1.5) + (2 * 2.0) = 1.0
+    }
+
+    {
+        dpfloat dpa = dpfloat(2.0, 1.0);
+        dpfloat dpb = dpfloat(1.5, 1.0);
+
+        __bwd_diff(j)(dpa, dpb, 1.0);
+
+        outputBuffer[3] = dpa.d; // Expect: 1
+        outputBuffer[4] = dpb.d; // Expect: 0
+    }
+
+    {
+        dpfloat dpa = dpfloat(2.0, 1.0);
+        dpfloat dpb = dpfloat(1.5, 1.0);
+
+        __bwd_diff(k)(dpa, dpb, 1.0);
+
+        outputBuffer[5] = dpa.d; // Expect: -1.5
+        outputBuffer[6] = dpb.d; // Expect: -2.0
+    }
+}
diff --git a/tests/autodiff/reverse-arithmetic.slang.expected.txt b/tests/autodiff/reverse-arithmetic.slang.expected.txt
new file mode 100644
index 000000000..297192e6c
--- /dev/null
+++ b/tests/autodiff/reverse-arithmetic.slang.expected.txt
@@ -0,0 +1,8 @@
+type: float
+1.000000
+7.000000
+1.000000
+1.000000
+0.000000
+-1.500000
+-2.000000