Fix condition declarations & assignments, enable logical operators in…

… for loops

These changes fix the differentiation of variable declarations in for
loop conditions that used to result into wrong derivatives. The commit
also tackles the problem of having an assignment operator that affects
the derivative in the for-loop condition, as well as adds support for
logical operators in for-loops and allows to combine assignments with
them.

Fixes: vgvassilev#273

include/clad/Differentiator/CladUtils.h

@@ -27,6 +27,10 @@ namespace clad {
     /// function `FD`.
     std::string ComputeEffectiveFnName(const clang::FunctionDecl* FD);
 
+    // Unwraps S to a single statement if it's a compound statement only
+    // containing 1 statement.
+    clang::Stmt* unwrapIfSingleStmt(clang::Stmt* S);
+
     /// Creates and returns a compound statement having statements as follows:
     /// {`S`, all the statement of `initial` in sequence}
     clang::CompoundStmt* PrependAndCreateCompoundStmt(clang::ASTContext& C,

lib/Differentiator/BaseForwardModeVisitor.cpp

@@ -668,18 +668,64 @@ StmtDiff BaseForwardModeVisitor::VisitForStmt(const ForStmt* FS) {
   const Stmt* init = FS->getInit();
   StmtDiff initDiff = init ? Visit(init) : StmtDiff{};
   addToCurrentBlock(initDiff.getStmt_dx());
-  VarDecl* condVarDecl = FS->getConditionVariable();
-  VarDecl* condVarClone = nullptr;
-  if (condVarDecl) {
-    DeclDiff<VarDecl> condVarResult = DifferentiateVarDecl(condVarDecl);
-    condVarClone = condVarResult.getDecl();
-    if (condVarResult.getDecl_dx())
-      addToCurrentBlock(BuildDeclStmt(condVarResult.getDecl_dx()));
+
+  StmtDiff condDiff = Clone(FS->getCond());
+  Expr* cond = condDiff.getExpr();
+
+  // Declaration in the condition (if any) needs to be differentiated.
+  if (VarDecl* condVarDecl = FS->getConditionVariable()) {
+    VarDecl* condVarClone =
+        BuildVarDecl(condVarDecl->getType(), condVarDecl->getNameAsString(),
+                     Clone(condVarDecl->getInit()), condVarDecl->isDirectInit(),
+                     nullptr, condVarDecl->getInitStyle());
+    VarDecl* _d_condVarDecl = BuildVarDecl(
+        condVarClone->getType(), "_d_" + condVarClone->getNameAsString(),
+        /*Init=*/nullptr, condVarClone->isDirectInit(), nullptr,
+        condVarClone->getInitStyle());
+    m_Variables.emplace(condVarClone, BuildDeclRef(_d_condVarDecl));
+    // Here we create a fictional cond that is equal to the assignment used in
+    // the declaration. The declaration itself is thrown before the for-loop
+    // without any init value. The fictional condition is then differentiated as
+    // a normal condition would be (see below). For example, the declaration
+    // inside `for (;double t = x;) {}` will be first processed into the
+    // following code:
+    // ```
+    // {
+    // double t;
+    // for (;t = x;) {}
+    // }
+    // ```
+    // which will then get differentiated normally as a for-loop with a
+    // differentiable condition in the next section.
+    auto condInit = condVarClone->getInit();
+    condVarClone->setInit(nullptr);
+    cond = BuildOp(BO_Assign, BuildDeclRef(condVarClone), condInit);
+    addToCurrentBlock(BuildDeclStmt(condVarClone));
+  }
+
+  // Condition differentiation.
+  // This adds support for assignments in conditions.
+  if (cond) {
+    cond = cond->IgnoreParenImpCasts();
+    // If it's a supported differentiable operator we wrap it back into
+    // parentheses and then visit. To ensure the correctness, a comma operator
+    // expression (cond_dx, cond) is generated and put instead of the condition.
+    // FIXME: Add support for other expressions in cond (unary operators,
+    // comparisons, function calls, etc.). Ideally, we should be able to simply
+    // always call Visit(cond)
+    BinaryOperator* condBO = dyn_cast<BinaryOperator>(cond);
+    if (condBO && (condBO->isLogicalOp() || condBO->isAssignmentOp())) {
+      condDiff = Visit(cond);
+      if (condDiff.getExpr_dx() && !isUnusedResult(condDiff.getExpr_dx()))
+        cond = BuildOp(BO_Comma, BuildParens(condDiff.getExpr_dx()),
+                       BuildParens(condDiff.getExpr()));
+      else
+        cond = condDiff.getExpr();
+    }
   }
-  Expr* cond = FS->getCond() ? Clone(FS->getCond()) : nullptr;
-  const Expr* inc = FS->getInc();
 
   // Differentiate the increment expression of the for loop
+  const Expr* inc = FS->getInc();
   beginBlock();
   StmtDiff incDiff = inc ? Visit(inc) : StmtDiff{};
   CompoundStmt* decls = endBlock();
@@ -714,27 +760,20 @@ StmtDiff BaseForwardModeVisitor::VisitForStmt(const ForStmt* FS) {
     incResult = incDiff.getExpr();
   }
 
+  // Build the derived for loop body.
   const Stmt* body = FS->getBody();
   beginScope(Scope::DeclScope);
   Stmt* bodyResult = nullptr;
-  if (isa<CompoundStmt>(body)) {
-    bodyResult = Visit(body).getStmt();
-  } else {
-    beginBlock();
-    StmtDiff Result = Visit(body);
-    for (Stmt* S : Result.getBothStmts())
-      addToCurrentBlock(S);
-    CompoundStmt* Block = endBlock();
-    if (Block->size() == 1)
-      bodyResult = Block->body_front();
-    else
-      bodyResult = Block;
-  }
+  beginBlock();
+  StmtDiff bodyVisited = Visit(body);
+  for (Stmt* S : bodyVisited.getBothStmts())
+    addToCurrentBlock(S);
+  bodyResult = utils::unwrapIfSingleStmt(endBlock());
   endScope();
 
-  Stmt* forStmtDiff =
-      new (m_Context) ForStmt(m_Context, initDiff.getStmt(), cond, condVarClone,
-                              incResult, bodyResult, noLoc, noLoc, noLoc);
+  Stmt* forStmtDiff = new (m_Context)
+      ForStmt(m_Context, initDiff.getStmt(), cond, /*condVar=*/nullptr,
+              incResult, bodyResult, noLoc, noLoc, noLoc);
 
   addToCurrentBlock(forStmtDiff);
   CompoundStmt* Block = endBlock();
@@ -1366,6 +1405,26 @@ BaseForwardModeVisitor::VisitBinaryOperator(const BinaryOperator* BinOp) {
     } else
       opDiff = BuildOp(BO_Comma, BuildParens(Ldiff.getExpr()),
                        BuildParens(Rdiff.getExpr_dx()));
+  } else if (BinOp->isLogicalOp()) {
+    // For (A && B) return ((dA, A) && (dB, B)) to ensure correct evaluation and
+    // correct derivative execution.
+    auto buildOneSide = [this](StmtDiff& Xdiff) {
+      if (Xdiff.getExpr_dx() && !isUnusedResult(Xdiff.getExpr_dx()))
+        return BuildParens(BuildOp(BO_Comma, BuildParens(Xdiff.getExpr_dx()),
+                                   BuildParens(Xdiff.getExpr())));
+      else
+        return BuildParens(Xdiff.getExpr());
+    };
+    // dLL = (dL, L)
+    Expr* dLL = buildOneSide(Ldiff);
+    // dRR = (dR, R)
+    Expr* dRR = buildOneSide(Rdiff);
+    opDiff = BuildOp(opCode, dLL, dRR);
+
+    // Since the both parts are included in the opDiff, there's no point in
+    // including it as a Stmt_dx. Moreover, the fact that Stmt_dx is left
+    // nullptr is used for treating expressions like ((A && B) && C) correctly.
+    return StmtDiff(opDiff, nullptr);
   }
   if (!opDiff) {
     // FIXME: add support for other binary operators

lib/Differentiator/CladUtils.cpp

@@ -102,6 +102,19 @@ namespace clad {
       }
     }
 
+    Stmt* unwrapIfSingleStmt(Stmt* S) {
+      if (!S)
+        return nullptr;
+      if (!isa<CompoundStmt>(S))
+        return S;
+      auto* CS = cast<CompoundStmt>(S);
+      if (CS->size() == 0)
+        return nullptr;
+      if (CS->size() == 1)
+        return CS->body_front();
+      return CS;
+    }
+
     CompoundStmt* PrependAndCreateCompoundStmt(ASTContext& C, Stmt* initial,
                                                Stmt* S) {
       llvm::SmallVector<Stmt*, 16> block;

lib/Differentiator/ReverseModeVisitor.cpp

@@ -783,19 +783,6 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     return StmtDiff(Forward, Reverse);
   }
 
-  static Stmt* unwrapIfSingleStmt(Stmt* S) {
-    if (!S)
-      return nullptr;
-    if (!isa<CompoundStmt>(S))
-      return S;
-    auto* CS = cast<CompoundStmt>(S);
-    if (CS->size() == 0)
-      return nullptr;
-    if (CS->size() == 1)
-      return CS->body_front();
-    return CS;
-  }
-
   StmtDiff ReverseModeVisitor::VisitIfStmt(const clang::IfStmt* If) {
     // Control scope of the IfStmt. E.g., in if (double x = ...) {...}, x goes
     // to this scope.
@@ -888,8 +875,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
         m_ExternalSource
             ->ActBeforeFinalizingVisitBranchSingleStmtInIfVisitStmt();
 
-      Stmt* Forward = unwrapIfSingleStmt(endBlock(direction::forward));
-      Stmt* Reverse = unwrapIfSingleStmt(BranchDiff.getStmt_dx());
+      Stmt* Forward = utils::unwrapIfSingleStmt(endBlock(direction::forward));
+      Stmt* Reverse = utils::unwrapIfSingleStmt(BranchDiff.getStmt_dx());
       return StmtDiff(Forward, Reverse);
     };
 
@@ -914,8 +901,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     CompoundStmt* ForwardBlock = endBlock(direction::forward);
     CompoundStmt* ReverseBlock = endBlock(direction::reverse);
     endScope();
-    return StmtDiff(unwrapIfSingleStmt(ForwardBlock),
-                    unwrapIfSingleStmt(ReverseBlock));
+    return StmtDiff(utils::unwrapIfSingleStmt(ForwardBlock),
+                    utils::unwrapIfSingleStmt(ReverseBlock));
   }
 
   StmtDiff ReverseModeVisitor::VisitConditionalOperator(
@@ -941,8 +928,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
       auto Result = DifferentiateSingleExpr(Branch, dfdx);
       StmtDiff BranchDiff = Result.first;
       StmtDiff ExprDiff = Result.second;
-      Stmt* Forward = unwrapIfSingleStmt(BranchDiff.getStmt());
-      Stmt* Reverse = unwrapIfSingleStmt(BranchDiff.getStmt_dx());
+      Stmt* Forward = utils::unwrapIfSingleStmt(BranchDiff.getStmt());
+      Stmt* Reverse = utils::unwrapIfSingleStmt(BranchDiff.getStmt_dx());
       return {StmtDiff(Forward, Reverse), ExprDiff};
     };
 
@@ -1128,7 +1115,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     Reverse = endBlock(direction::reverse);
     endScope();
 
-    return {unwrapIfSingleStmt(Forward), unwrapIfSingleStmt(Reverse)};
+    return {utils::unwrapIfSingleStmt(Forward),
+            utils::unwrapIfSingleStmt(Reverse)};
   }
 
   StmtDiff
@@ -2766,7 +2754,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
       addToCurrentBlock(SDiff.getStmt_dx(), direction::reverse);
     CompoundStmt* RCS = endBlock(direction::reverse);
     std::reverse(RCS->body_begin(), RCS->body_end());
-    Stmt* ReverseResult = unwrapIfSingleStmt(RCS);
+    Stmt* ReverseResult = utils::unwrapIfSingleStmt(RCS);
     return StmtDiff(SDiff.getStmt(), ReverseResult);
   }
 
@@ -2780,7 +2768,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     CompoundStmt* RCS = endBlock(direction::reverse);
     Stmt* ForwardResult = endBlock(direction::forward);
     std::reverse(RCS->body_begin(), RCS->body_end());
-    Stmt* ReverseResult = unwrapIfSingleStmt(RCS);
+    Stmt* ReverseResult = utils::unwrapIfSingleStmt(RCS);
     return {StmtDiff(ForwardResult, ReverseResult), EDiff};
   }
 
@@ -2929,7 +2917,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
       for (Decl* decl : decls)
         addToBlock(BuildDeclStmt(decl), m_Globals);
       Stmt* initAssignments = MakeCompoundStmt(inits);
-      initAssignments = unwrapIfSingleStmt(initAssignments);
+      initAssignments = utils::unwrapIfSingleStmt(initAssignments);
       return StmtDiff(initAssignments);
     }
 
@@ -3574,7 +3562,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
       if (m_ExternalSource)
         m_ExternalSource->ActAfterProcessingSingleStmtBodyInVisitForLoop();
 
-      Stmt* reverseBlock = unwrapIfSingleStmt(bodyDiff.getStmt_dx());
+      Stmt* reverseBlock = utils::unwrapIfSingleStmt(bodyDiff.getStmt_dx());
       bodyDiff = {endBlock(direction::forward), reverseBlock};
       // for forward-pass loop statement body
       endScope();
@@ -3619,7 +3607,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
     addToCurrentBlock(condVarDiff, direction::reverse);
     addToCurrentBlock(bodyDiff.getStmt_dx(), direction::reverse);
     bodyDiff = {bodyDiff.getStmt(),
-                unwrapIfSingleStmt(endBlock(direction::reverse))};
+                utils::unwrapIfSingleStmt(endBlock(direction::reverse))};
     return bodyDiff;
   }
 

test/FirstDerivative/Loops.C

@@ -377,8 +377,8 @@ double fn10_darg0(double x, size_t n);
 // CHECK-NEXT:     double res = 0;
 // CHECK-NEXT:     {
 // CHECK-NEXT:         size_t _d_count = 0;
-// CHECK-NEXT:         size_t _d_max_count = _d_n;
-// CHECK-NEXT:         for (size_t count = 0; {{.*}}max_count{{.*}}; ++count) {
+// CHECK-NEXT:         size_t max_count;
+// CHECK-NEXT:         for (size_t count = 0; (_d_max_count = _d_n) , (max_count = n); ++count) {
 // CHECK-NEXT:             if (count >= max_count)
 // CHECK-NEXT:                 break;
 // CHECK-NEXT:             {
@@ -393,6 +393,81 @@ double fn10_darg0(double x, size_t n);
 // CHECK-NEXT:     return _d_res;
 // CHECK-NEXT: }
 
+double fn11(double x, double y) {
+    double r = 0;
+    for (int i = 0; (r = x); ++i) {
+        if (i == 3) break;
+        r += x;
+    }
+    return r;
+} // fn11(x,y) == x
+
+double fn11_darg0(double x, double y);
+// CHECK:      double fn11_darg0(double x, double y) {
+// CHECK-NEXT:          double _d_x = 1;
+// CHECK-NEXT:          double _d_y = 0;
+// CHECK-NEXT:          double _d_r = 0;
+// CHECK-NEXT:          double r = 0;
+// CHECK-NEXT:          {
+// CHECK-NEXT:              int _d_i = 0;
+// CHECK-NEXT:              for (int i = 0; (_d_r = _d_x) , (r = x); ++i) {
+// CHECK-NEXT:                      if (i == 3)
+// CHECK-NEXT:                          break;
+// CHECK-NEXT:                      _d_r += _d_x;
+// CHECK-NEXT:                      r += x;
+// CHECK-NEXT:              }
+// CHECK-NEXT:          }
+// CHECK-NEXT:          return _d_r;
+// CHECK-NEXT:      }
+
+double fn12(double x, double y) {
+    double r = 0;
+    for (int i = 0; double c = x; ++i) {
+        if (i == 3) break;
+        c += x;
+        r = c;
+    }
+    return r;
+} // fn11(x,y) == 2*x
+
+double fn12_darg0(double x, double y);
+// CHECK:      double fn12_darg0(double x, double y) {
+// CHECK-NEXT:          double _d_x = 1;
+// CHECK-NEXT:          double _d_y = 0;
+// CHECK-NEXT:          double _d_r = 0;
+// CHECK-NEXT:          double r = 0;
+// CHECK-NEXT:          {
+// CHECK-NEXT:              int _d_i = 0;
+// CHECK-NEXT:              double c;
+// CHECK-NEXT:              for (int i = 0; (_d_c = _d_x) , (c = x); ++i) {
+// CHECK-NEXT:                      if (i == 3)
+// CHECK-NEXT:                          break;
+// CHECK-NEXT:                      _d_c += _d_x;
+// CHECK-NEXT:                      c += x;
+// CHECK-NEXT:                      _d_r = _d_c;
+// CHECK-NEXT:                      r = c;
+// CHECK-NEXT:              }
+// CHECK-NEXT:          }
+// CHECK-NEXT:          return _d_r;
+// CHECK-NEXT:      }
+
+double fn13(double u, double v) {
+    double res = 0;
+    for (; (res = u * v) && (u = 0) ;) {}
+    return res;
+} // = u*v
+
+double fn13_darg0(double u, double v);
+// CHECK:           double fn13_darg0(double u, double v) {
+// CHECK-NEXT:               double _d_u = 1;
+// CHECK-NEXT:               double _d_v = 0;
+// CHECK-NEXT:               double _d_res = 0;
+// CHECK-NEXT:               double res = 0;
+// CHECK-NEXT:               for (; ((_d_res = _d_u * v + u * _d_v) , (res = u * v)) && ((_d_u = 0) , (u = 0));) {
+// CHECK-NEXT:               }
+// CHECK-NEXT:               return _d_res;
+// CHECK-NEXT:           }
+
 #define TEST(fn)\
 auto d_##fn = clad::differentiate(fn, "i");\
 printf("%.2f\n", d_##fn.execute(3, 5));
@@ -430,4 +505,20 @@ int main() {
 
   clad::differentiate(fn10, 0);
   printf("Result is = %.2f\n", fn10_darg0(3, 5)); // CHECK-EXEC: Result is = 30.00
+
+  clad::differentiate(fn11, 0);
+  printf("Result is = %.2f\n", fn11_darg0(3, 5)); // CHECK-EXEC: Result is = 1.00
+  printf("Result is = %.2f\n", fn11_darg0(-3, 6)); // CHECK-EXEC: Result is = 1.00
+  printf("Result is = %.2f\n", fn11_darg0(1, 5)); // CHECK-EXEC: Result is = 1.00
+
+  clad::differentiate(fn12, 0);
+  printf("Result is = %.2f\n", fn12_darg0(3, 5)); // CHECK-EXEC: Result is = 2.00
+  printf("Result is = %.2f\n", fn12_darg0(-3, 6)); // CHECK-EXEC: Result is = 2.00
+  printf("Result is = %.2f\n", fn12_darg0(1, 5)); // CHECK-EXEC: Result is = 2.00
+
+  clad::differentiate(fn13, 0);
+  printf("Result is = %.2f\n", fn13_darg0(3, 4)); // CHECK-EXEC: Result is = 4.00
+  printf("Result is = %.2f\n", fn13_darg0(-3, 5)); // CHECK-EXEC: Result is = 5.00
+  printf("Result is = %.2f\n", fn13_darg0(1, 6)); // CHECK-EXEC: Result is = 6.00
+
 }