Fix ICE when immutable value is passed to a bwd_diff function. (#7973)

4 files changed, 31 insertions, 4 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 31b08e925..f70760c5d 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -2703,10 +2703,14 @@ void SemanticsVisitor::maybeDiagnoseConstVariableAssignment(Expr* expr)
         {
             e = subscriptExpr->baseExpression;
         }
-        else
+        else if (as<ThisExpr>(e))
         {
             break;
         }
+        else
+        {
+            return;
+        }
     }
 
     // Check if we're trying to assign to a non-l-value (const variable, immutable member, etc.)
@@ -2979,7 +2983,9 @@ Expr* SemanticsVisitor::CheckInvokeExprWithCheckedOperands(InvokeExpr* expr)
                             else if (!as<ErrorType>(argExpr->type))
                             {
                                 // Emit additional diagnostic for invalid pointer taking operations
-                                auto funcDeclRef = getDeclRef(m_astBuilder, funcDeclRefExpr);
+                                auto funcDeclRef = funcDeclRefExpr
+                                                       ? getDeclRef(m_astBuilder, funcDeclRefExpr)
+                                                       : DeclRef<Decl>();
                                 if (funcDeclRef)
                                 {
                                     auto knownBuiltinAttr =
diff --git a/tests/diagnostics/implicit-cast-lvalue.slang.expected b/tests/diagnostics/implicit-cast-lvalue.slang.expected
index 93217b239..10ebfc656 100644
--- a/tests/diagnostics/implicit-cast-lvalue.slang.expected
+++ b/tests/diagnostics/implicit-cast-lvalue.slang.expected
@@ -7,7 +7,6 @@ tests/diagnostics/implicit-cast-lvalue.slang(19): error 30047: argument passed t
     a(y);
       ^
 tests/diagnostics/implicit-cast-lvalue.slang(19): note 30063: argument was implicitly cast from 'double' to 'float', and Slang does not support using an implicit cast as an l-value with this type
-tests/diagnostics/implicit-cast-lvalue.slang(19): note 30049: attempting to assign to a const variable or immutable member; use '[mutating]' attribute on the containing method to allow modification
 }
 standard output = {
 }
diff --git a/tests/diagnostics/lvalue-in-bwd-diff.slang b/tests/diagnostics/lvalue-in-bwd-diff.slang
new file mode 100644
index 000000000..2e12bf5c0
--- /dev/null
+++ b/tests/diagnostics/lvalue-in-bwd-diff.slang
@@ -0,0 +1,23 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+[Differentiable]
+float square(float x, float y)
+{
+    return x * x + y * y;
+}
+
+void main()
+{
+    // Forward mode differentiation
+    let x = diffPair(3.0, 1.0); // x = 3, 𝜕x/𝜕𝛉 = 1
+    let y = diffPair(4.0, 1.0); // y = 4, 𝜕y/𝜕𝛄 = 1
+    let result = fwd_diff(square)(x, y);
+    printf("dResult: %f\n", result.d);
+
+    // Backward mode differentiation
+    let dLdSquare = 1.0f;
+    // CHECK-NOT: error 30049
+    // CHECK: error 30047
+    // CHECK-NOT: error 30049
+    bwd_diff(square)(x, y, dLdSquare);
+    printf("dL/dx: %f, dL/dy: %f\n", x.d, y.d);
+}
diff --git a/tests/diagnostics/methods/mutating-method-on-rvalue.slang.expected b/tests/diagnostics/methods/mutating-method-on-rvalue.slang.expected
index d9694276b..066c8439d 100644
--- a/tests/diagnostics/methods/mutating-method-on-rvalue.slang.expected
+++ b/tests/diagnostics/methods/mutating-method-on-rvalue.slang.expected
@@ -7,7 +7,6 @@ tests/diagnostics/methods/mutating-method-on-rvalue.slang(13): note 30049: attem
 tests/diagnostics/methods/mutating-method-on-rvalue.slang(25): error 30050: mutating method 'increment' cannot be called on an immutable value
     gCounter.increment();
                       ^
-tests/diagnostics/methods/mutating-method-on-rvalue.slang(25): note 30049: attempting to assign to a const variable or immutable member; use '[mutating]' attribute on the containing method to allow modification
 }
 standard output = {
 }