Fix the derivative of string literals in forward mode

This commit makes Clad set the derivative of string literals to an empty string in the forward mode. Differentiating string literals used to produce integer zero literals previously.
gojakuch · Jul 4, 2024 · 4ac8ca5 · 4ac8ca5
1 parent 645d2b6
commit 4ac8ca5
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Showing 2 changed files with 36 additions and 4 deletions.
diff --git a/lib/Differentiator/BaseForwardModeVisitor.cpp b/lib/Differentiator/BaseForwardModeVisitor.cpp
@@ -1662,10 +1662,9 @@ BaseForwardModeVisitor::VisitCharacterLiteral(const CharacterLiteral* CL) {
 }
 
 StmtDiff BaseForwardModeVisitor::VisitStringLiteral(const StringLiteral* SL) {
-  llvm::APInt zero(m_Context.getIntWidth(m_Context.IntTy), /*value*/ 0);
-  auto* constant0 =
-      IntegerLiteral::Create(m_Context, zero, m_Context.IntTy, noLoc);
-  return StmtDiff(Clone(SL), constant0);
+  return StmtDiff(Clone(SL), StringLiteral::Create(
+                                 m_Context, "", SL->getKind(), SL->isPascal(),
+                                 SL->getType(), utils::GetValidSLoc(m_Sema)));
 }
 
 StmtDiff BaseForwardModeVisitor::VisitWhileStmt(const WhileStmt* WS) {

diff --git a/test/FirstDerivative/Variables.C b/test/FirstDerivative/Variables.C
@@ -4,6 +4,7 @@
 
 #include "clad/Differentiator/Differentiator.h"
 #include <cmath>
+#include <string>
 
 double f_x(double x) {
   double t0 = x;
@@ -86,12 +87,44 @@ double f_sin(double x, double y) {
 // CHECK-NEXT:     return _d_xt + _d_yt;
 // CHECK-NEXT: }
 
+double f_string(double x) {
+  const char *s = "string literal";
+  return x;
+}
+
+// CHECK: double f_string_darg0(double x) {
+// CHECK-NEXT:     double _d_x = 1;
+// CHECK-NEXT:     const char *_d_s = "";
+// CHECK-NEXT:     const char *s = "string literal";
+// CHECK-NEXT:     return _d_x;
+// CHECK-NEXT: }
+
+namespace clad {
+namespace custom_derivatives {
+clad::ValueAndPushforward<double, double> string_test_pushforward(double x, const char s[], double _d_x, const char *_d_s) {
+    return {0, 0};
+}
+}}
+double string_test(double x, const char s[]) {
+    return 1;
+}
+double f_string_call(double x) {
+  return string_test(x, "string literal");
+}
+
+// CHECK: double f_string_call_darg0(double x) {
+// CHECK-NEXT:         double _d_x = 1;
+// CHECK-NEXT:         clad::ValueAndPushforward<double, double> _t0 = clad::custom_derivatives::string_test_pushforward(x, "string literal", _d_x, "");
+// CHECK-NEXT:         return _t0.pushforward;
+// CHECK-NEXT:     }
 
 int main() {
   clad::differentiate(f_x, 0);
   clad::differentiate(f_ops1, 0);
   clad::differentiate(f_ops2, 0);
   clad::differentiate(f_sin, 0);
+  clad::differentiate(f_string, 0);
+  clad::differentiate(f_string_call, 0);
 }